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2016PhRvD..94l4027F

Construction of regular black holes in general relativity

2016-01-01

['-', '-']

[]

We present a general procedure for constructing exact black hole solutions with electric or magnetic charges in general relativity coupled to a nonlinear electrodynamics. We obtain a variety of two-parameter family spherically symmetric black hole solutions. In particular, the singularity at the center of the space-time can be canceled in the parameter space and the black hole solutions become regular everywhere in space-time. We study the global properties of the solutions and derive the first law of thermodynamics. We also generalize the procedure to include a cosmological constant and construct regular black hole solutions that are asymptotic to anti-de Sitter space-time.

[]

https://arxiv.org/pdf/1610.02636.pdf

2004MNRAS.354..292K

Massive black hole seeds from low angular momentum material

2004-01-01

['galaxies formation', 'galaxies structure', 'cosmology theory', 'cosmology dark matter', 'astrophysics']

[]

We present a cosmologically motivated model in which the seeds of supermassive black holes form out of the lowest angular momentum gas in protogalaxies at high redshift. We show that, under reasonable assumptions, this leads naturally to a correlation between black hole masses and spheroid properties, as observed today. We assume that the gas in early-forming, rare-peak haloes has a distribution of specific angular momentum similar to that derived for the dark matter in cosmological N-body simulations. This distribution has a significant low angular momentum tail, which implies that every protogalaxy should contain gas that ends up in a high-density disc. In haloes more massive than a critical threshold of ~7 × 10<SUP>7</SUP> M<SUB>solar</SUB> at z~ 15, the discs are gravitationally unstable, and experience an efficient Lin-Pringle viscosity that transfers angular momentum outwards and allows mass inflow. We assume that this process continues until the first massive stars disrupt the disc. The seed black holes created in this manner have a characteristic mass of ~10<SUP>5</SUP> M<SUB>solar</SUB>, roughly independent of the redshift of formation. This serves as a lower bound for black hole masses at galactic centres today. The comoving mass density in black hole seeds grows with time, tracking the continuous production of critical-mass haloes, and saturates when cosmic reionization acts to prevent gas cooling in these low-mass systems. By z~ 15, the comoving mass density becomes comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. The hierarchical merger process after z~ 15 naturally leads to a linear correlation between black hole mass and stellar spheroid mass, with negligible black hole masses in disc-dominated galaxies. The formation of massive seeds at high redshifts, and the relatively important role of mergers in the buildup of today's black holes, are key elements in the proposed scenario.

[]

https://arxiv.org/pdf/astro-ph/0311487.pdf

2014MNRAS.444L.100D

The role of the reflection fraction in constraining black hole spin.

2014-01-01

['accretion', 'accretion disks', 'black hole physics', 'line profiles', 'galaxies active', 'galaxies nuclei', '-']

[]

In many active galaxies, the X-ray reflection features from the innermost regions of the accretion disc are relativistically distorted. This distortion allows us to measure parameters of the black hole such as its spin. The ratio in flux between the direct and the reflected radiation, the so-called reflection fraction, is determined directly from the geometry and location of primary source of radiation. We calculate the reflection fraction in the lamp post geometry in order to determine its maximal possible value for a given value of black hole spin. We show that high reflection fractions in excess of two are only possible for rapidly rotating black holes, suggesting that the high spin sources produce the strongest relativistic reflection features. Using simulations we show that taking this constraint into account does significantly improve the determination of the spin values. We make software routines for the most popular X-ray data analysis packages available that incorporate these additional constraints.

[]

https://arxiv.org/pdf/1408.2347.pdf

2012Sci...337..544V

The Formation and Evolution of Massive Black Holes

2012-01-01

['-', '-', '-']

[]

The past 10 years have witnessed a change of perspective in the way astrophysicists think about massive black holes (MBHs), which are now considered to have a major role in the evolution of galaxies. This appreciation was driven by the realization that black holes of millions of solar masses and above reside in the center of most galaxies, including the Milky Way. MBHs also powered active galactic nuclei known to exist just a few hundred million years after the Big Bang. Here, I summarize the current ideas on the evolution of MBHs through cosmic history, from their formation about 13 billion years ago to their growth within their host galaxies.

[]

https://arxiv.org/pdf/1208.1106.pdf

1997ApJ...479L.145B

An Unstable Central Disk in the Superluminal Black Hole X-Ray Binary GRS 1915+105

1997-01-01

['accretion', 'accretion disks', 'stars binaries close', 'black hole physics', 'instabilities', 'astronomy x rays', '-', 'accretion', 'accretion disks', 'stars binaries close', 'black hole physics', '-', 'astronomy x rays', 'astrophysics']

[]

We have analyzed the X-ray spectra of the microquasar GRS 1915+105, as observed with the Proportional Counter Array (PCA) on the Rossi X-Ray Timing Explorer, during periods of stable weak emission, outbursts, and rapid flaring. We find that the complicated X-ray intensity curve of this source can be described by the rapid removal and replenishment of matter forming the inner part of an optically thick accretion disk, probably caused by a thermal-viscous instability analogous to that operating in dwarf novae, but here driven by the Lightman-Eardley instability. We find that the mass accretion rate in quiescence is about 10<SUP>-6</SUP> M<SUB>solar</SUB> yr<SUP>-1</SUP>. Only a small fraction of the energy liberated by accretion is emitted as radiation. We suggest that most of this energy is advected into the black hole in the high-viscosity state of the outburst cycle.

[]

https://arxiv.org/pdf/astro-ph/9702048.pdf

2020SciA....6.1310J

Universal interferometric signatures of a black hole's photon ring

2020-01-01

['-', '-', '-', '-', '-']

[]

The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin "photon ring," which is composed of an infinite sequence of self-similar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole "shadow," becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high order subrings. Here, we show that these subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.

[]

https://arxiv.org/pdf/1907.04329.pdf

2014MNRAS.439..503S

Numerical simulations of super-critical black hole accretion flows in general relativity

2014-01-01

['accretion', 'accretion disks', 'black hole physics', 'relativity', 'methods numerical', 'galaxies jets', '-']

[]

A new general relativistic radiation magnetohydrodynamical code KORAL is described, which employs the M1 scheme to close the radiation moment equations. The code has been successfully verified against a number of tests. Axisymmetric simulations of super-critical magnetized accretion on non-rotating (a<SUB>*</SUB> = 0.0) and spinning (a<SUB>*</SUB> = 0.9) black holes are presented. The accretion rates in the two models are dot{M}≈ 100-200 dot{M}_Edd. These first general relativistic simulations of super-critical black hole accretion are potentially relevant to tidal disruption events and hyper-accreting supermassive black holes in the early Universe. Both simulated models are optically and geometrically thick, and have funnels through which energy escapes in the form of relativistic gas, Poynting flux and radiative flux. The jet is significantly more powerful in the a<SUB>*</SUB> = 0.9 run. The net energy outflow rate in the two runs correspond to efficiencies of 5 per cent (a<SUB>*</SUB> = 0) and 33 per cent (a<SUB>*</SUB> = 0.9), as measured with respect to the mass accretion rate at the black hole. These efficiencies agree well with those measured in previous simulations of non-radiative geometrically thick discs. Furthermore, in the a<SUB>*</SUB> = 0.9 run, the outflow power appears to originate in the spinning black hole, suggesting that the associated physics is again similar in non-radiative and super-critical accretion flows. While the two simulations are efficient in terms of total energy outflow, both runs are radiatively inefficient. Their luminosities are only ∼1-10L<SUB>Edd</SUB>, which corresponds to a radiative efficiency ∼0.1 per cent. Interestingly, most of the radiative luminosity emerges through the funnels where the local radiative flux is highly super-Eddington.

[]

https://arxiv.org/pdf/1311.5900.pdf

2007MNRAS.374..515L

Starbursts near supermassive black holes: young stars in the Galactic Centre, and gravitational waves in LISA band

2007-01-01

['accretion', 'accretion disks', 'stars fundamental parameters', 'astrophysics']

[]

We propose a scenario in which massive stars form in a self-gravitating gaseous disc around a supermassive black hole (SMBH). We analyse the dynamics of a disc forming around an SMBH, in which the angular momentum is transported by turbulence induced by the disc's self-gravity. We find that once the surface density of the disc exceeds a critical value, the disc fragments into dense clumps. We argue that the clumps accrete material from the remaining disc and merge into larger clumps; the upper mass of a merged clump is a few tens to a few hundreds of solar mass. <P />This picture fits well with the observed young stellar discs near the SgrA* black hole in the Galactic Centre. In particular, we show how the masses and spatial distribution of the young stars, and the total mass in the Galactic Centre discs can be explained. However, explaining the origin of the several young stars closest to the black hole (the S-stars) is more problematic: their orbits are compact, eccentric, and have random orientation. We propose that the S-stars were born in a previous starburst(s), and then migrated through their parent disc via type-I or runaway migration. Their orbits were then randomized by the Rauch-Tremaine resonant relaxation. <P />We then explore the consequences of the star formation scenario for AGN discs, which are continuously resupplied with gas. We argue that some compact remnants generated by the starburst will get embedded in the disc. The disc-born stellar mass black holes will interact gravitationally with the massive accretion disc and be dragged towards the central black hole. Merger of a disc-born black hole with the central black hole will produce a burst of gravitational waves. If the central black hole is accreting at a rate comparable to the Eddington limit, the gas drag from the accretion disc will not alter significantly the dynamics of the final year of merger, and the gravitational waves should be observable by Laser Interferometer Space Antenna (LISA). For a reasonable range of parameters such mergers will be detected monthly, and that the gravitational-wave signal from these mergers is distinct from that of other merger scenarios. Also, for some plausible black hole masses and accretion rates, the burst of gravitational waves should be accompanied by a detectable change in the optical luminosity of the central engine.

[]

https://arxiv.org/pdf/astro-ph/0603583.pdf

2019JCAP...02..018R

Formation and evolution of primordial black hole binaries in the early universe

2019-01-01

['-', '-', '-']

[]

The abundance of primordial black holes (PBHs) in the mass range 0.1-10<SUP>3</SUP> M<SUB>solar</SUB> can potentially be tested by gravitational wave observations due to the large merger rate of PBH binaries formed in the early universe. To put the estimates of the latter on a firmer footing, we first derive analytical PBH merger rate for general PBH mass functions while imposing a minimal initial comoving distance between the binary and the PBH nearest to it, in order to pick only initial configurations where the binary would not get disrupted. We then study the formation and evolution of PBH binaries before recombination by performing N-body simulations. We find that the analytical estimate based on the tidally perturbed 2-body system strongly overestimates the present merger rate when PBHs comprise all dark matter, as most initial binaries are disrupted by the surrounding PBHs. This is mostly due to the formation of compact N-body systems at matter-radiation equality. However, if PBHs make up a small fraction of the dark matter, f<SUB>PBH</SUB> lesssim 10%, these estimates become more reliable. In that case, the merger rate observed by LIGO imposes the strongest constraint on the PBH abundance in the mass range 2-160 M<SUB>solar</SUB>. Finally, we argue that, even if most initial PBH binaries are perturbed, the present BH-BH merger rate of binaries formed in the early universe is larger than Script O(10) Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> f<SUB>PBH</SUB><SUP>3</SUP>.

[]

https://arxiv.org/pdf/1812.01930.pdf

2024A&A...691A.145M

JADES: The diverse population of infant black holes at 4 &lt; z &lt; 11: Merging, tiny, poor, but mighty

2024-01-01

['galaxies active', 'galaxies formation', 'galaxies photometry', 'galaxies nuclei', 'galaxies quasars', '-', '-', '-']

[]

Spectroscopy with the James Webb Space Telescope has opened the possibility of identifying moderate-luminosity active galactic nuclei (AGNs) in the early Universe, at and beyond the epoch of re-ionisation, complementing previous surveys of much more luminous (and much rarer) quasars. We present 12 new AGNs at 4 &lt; z &lt; 7 in the JADES survey (in addition to the previously identified AGN in GN-z11 at z = 10.6) revealed through the detection of a broad-line region (BLR) seen in the Balmer emission lines. The depth of JADES, together with the use of three different spectral resolutions, enables us to probe a lower-mass regime relative to previous studies. In a few cases, we find evidence for two broad components of Hα, which suggests that these could be candidate merging black holes (BHs), although a complex BLR geometry cannot be excluded. The inferred BH masses range from 8 × 10<SUP>7</SUP> M<SUB>⊙</SUB> down to 4 × 10<SUP>5</SUP> M<SUB>⊙</SUB>, interestingly probing the regime expected for direct collapse BHs. The inferred AGN bolometric luminosities (∼10<SUP>44</SUP> ‑ 10<SUP>45</SUP> erg/s) imply accretion rates that are &lt; 0.5 times the Eddington rate in most cases. However, small BHs, with M<SUB>BH</SUB> ∼ 10<SUP>6</SUP> M<SUB>⊙</SUB>, tend to accrete at Eddington or super-Eddington rates. These BHs at z ∼ 4–11 are over-massive relative to their host galaxies' stellar masses when compared to the local M<SUB>BH</SUB> ‑ M<SUB>star</SUB> relation, even approaching M<SUB>BH</SUB> ∼ M<SUB>star</SUB>, as was expected from heavy BH seeds and/or super-Eddington accretion scenarios. However, we find that these early BHs tend to be more consistent with the local relation between M<SUB>BH</SUB> and velocity dispersion, as well as between M<SUB>BH</SUB> and dynamical mass, suggesting that these are more fundamental and universal relations. On the classical, optical narrow-line excitation-diagnostic diagrams, these AGNs are located in the region that is locally occupied by star-forming galaxies, implying that they would be missed by the standard classification techniques if they did not display broad lines. Their location on the diagram is consistent with what is expected for AGNs hosted in metal-poor galaxies (Z ∼ 0.1 ‑ 0.2 Z<SUB>⊙</SUB>). The fraction of broad-line AGNs with L<SUB>AGN</SUB> &gt; 10<SUP>44</SUP> erg/s among galaxies in the redshift range of 4 &lt; z &lt; 6 is about 10%, suggesting that the contribution of AGNs and their hosts to the re-ionisation of the Universe is &gt; 10%.

[]

https://arxiv.org/pdf/2308.01230.pdf

2010MNRAS.402.1249S

Supermassive black hole formation by direct collapse: keeping protogalactic gas H<SUB>2</SUB> free in dark matter haloes with virial temperatures T<SUB>vir</SUB> &gt; rsim 10<SUP>4</SUP> K

2010-01-01

['black hole physics', 'methods numerical', 'cosmology theory', '-']

[]

In the absence of H<SUB>2</SUB> molecules, the primordial gas in early dark matter haloes with virial temperatures just above T<SUB>vir</SUB> &gt;~ 10<SUP>4</SUP>K cools by collisional excitation of atomic H. Although it cools efficiently, this gas remains relatively hot, at a temperature near T ~ 8000 K, and consequently might be able to avoid fragmentation and collapse directly into a supermassive black hole. In order for H<SUB>2</SUB> formation and cooling to be strongly suppressed, the gas must be irradiated by a sufficiently intense ultraviolet (UV) flux. We performed a suite of three-dimensional hydrodynamical adaptive mesh refinement (AMR) simulations of gas collapse in three different protogalactic haloes with T<SUB>vir</SUB> &gt;~ 10<SUP>4</SUP>K, irradiated by a UV flux with various intensities and spectra. We determined the critical specific intensity, J<SUP>crit</SUP><SUB>21</SUB>, required to suppress H<SUB>2</SUB> cooling in each of the three haloes. For a hard spectrum representative of metal-free stars, we find (in units of 10<SUP>-21</SUP>ergs<SUP>-1</SUP>Hz<SUP>-1</SUP>sr<SUP>-1</SUP>cm<SUP>-2</SUP>) 10<SUP>4</SUP> &lt; J<SUP>crit</SUP><SUB>21</SUB> &lt; 10<SUP>5</SUP>, while for a softer spectrum, which is characteristic of a normal stellar population, and for which H<SUP>-</SUP> dissociation is important, we find 30 &lt; J<SUP>crit</SUP><SUB>21</SUB> &lt; 300. These values are a factor of 3-10 lower than previous estimates. We attribute the difference to the higher, more accurate H<SUB>2</SUB> collisional dissociation rate we adopted. The reduction in J<SUP>crit</SUP><SUB>21</SUB> exponentially increases the number of rare haloes exposed to supercritical radiation. When H<SUB>2</SUB> cooling is suppressed, gas collapse starts with a delay, but it ultimately proceeds more rapidly. The infall velocity is near the increased sound speed, and an object as massive as M ~ 10<SUP>5</SUP>M<SUB>solar</SUB> may form at the centre of these haloes, compared to the M ~ 10<SUP>2</SUP>M<SUB>solar</SUB> stars forming when H<SUB>2</SUB> cooling is efficient.

[]

https://arxiv.org/pdf/0906.4773.pdf

2007PhLB..645..261A

Non-commutative geometry inspired charged black holes

2007-01-01

['-', '-']

[]

We find a new, non-commutative geometry inspired, solution of the coupled Einstein-Maxwell field equations describing a variety of charged, self-gravitating objects, including extremal and non-extremal black holes. The metric smoothly interpolates between de Sitter geometry, at short distance, and Reissner-Nordstrøm geometry far away from the origin. Contrary to the ordinary Reissner-Nordstrøm spacetime there is no curvature singularity in the origin neither “naked” nor shielded by horizons. We investigate both Hawking process and pair creation in this new scenario.

[]

https://arxiv.org/pdf/gr-qc/0612035.pdf

2001Natur.411..662C

An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars

2001-01-01

['astrophysics']

[]

The study of astronomical objects using electromagnetic radiation involves four basic observational approaches: imaging, spectroscopy, photometry (accurate counting of the photons received) and polarimetry (measurement of the polarizations of the observed photons). In contrast to observations at other wavelengths, a lack of sensitivity has prevented X-ray astronomy from making use of polarimetry. Yet such a technique could provide a direct picture of the state of matter in extreme magnetic and gravitational fields, and has the potential to resolve the internal structures of compact sources that would otherwise remain inaccessible, even to X-ray interferometry. In binary pulsars, for example, we could directly `see' the rotation of the magnetic field and determine if the emission is in the form of a `fan' or a `pencil' beam. Also, observation of the characteristic twisting of the polarization angle in other compact sources would reveal the presence of a black hole. Here we report the development of an instrument that makes X-ray polarimetry possible. The factor of 100 improvement in sensitivity that we have achieved will allow direct exploration of the most dramatic objects of the X-ray sky.

[]

https://arxiv.org/pdf/astro-ph/0107486.pdf

1996PhRvL..77..428M

Statistical Entropy of Four-Dimensional Extremal Black Holes

1996-01-01

['-']

[]

String theory is used to count microstates of four-dimensional extremal black holes in compactifications with N = 4 and N = 8 supersymmetry. The result agrees for large charges with the Bekenstein-Hawking entropy.

[]

https://arxiv.org/pdf/hep-th/9603060.pdf

2004JHEP...02..006G

Supersymmetric AdS<SUB>5</SUB> black holes

2004-01-01

['black hole physics', '-', '-']

[]

The first examples of supersymmetric, asymptotically AdS<SUB>5</SUB>, black hole solutions are presented. They form a 1-parameter family of solutions of minimal five-dimensional gauged supergravity. Their angular momentum can never vanish. The solutions are obtained by a systematic analysis of supersymmetric solutions with Killing horizons. Other new examples of such solutions are obtained. These include solutions for which the horizon is a homogeneous Nil or SL(2,Bbb R) manifold.

[]

https://arxiv.org/pdf/hep-th/0401042.pdf

2002Sci...297.1310M

Tracing Black Hole Mergers Through Radio Lobe Morphology

2002-01-01

['-', 'astrophysics']

[]

Binary supermassive black holes are produced by galactic mergers as the black holes from the two galaxies fall to the center of the merged system and form a bound pair. The two black holes will eventually coalesce in an enormous burst of gravitational radiation. Here we show that the orientation of a black hole's spin axis would change dramatically even in a minor merger, leading to a sudden flip in the direction of any associated jet. We identify the winged or X-type radio sources with galaxies in which this has occurred. The inferred coalescence rate is similar to the overall galaxy merger rate, implying that of the order of one merger event per year could be detected by gravitational wave interferometers.

[]

https://arxiv.org/pdf/astro-ph/0208001.pdf

2015CQGra..32n4001H

Construction and physical properties of Kerr black holes with scalar hair

2015-01-01

['black hole physics', '-', 'methods numerical', '-', '-', '-']

[]

Kerr black holes (BHs) with scalar hair are solutions of the Einstein-Klein-Gordon field equations describing regular (on and outside an event horizon), asymptotically flat BHs with scalar hair (Herdeiro and Radu 2014 Phys. Rev. Lett. 112 221101). These BHs interpolate continuously between the Kerr solution and rotating boson stars in D = 4 spacetime dimensions. Here we provide details on their construction, discussing properties of the ansatz, the field equations, the boundary conditions and the numerical strategy. Then, we present an overview of the parameter space of the solutions, and describe in detail the space-time structure of the BH's exterior geometry and of the scalar field for a sample of reference solutions. Phenomenological properties of potential astrophysical interest are also discussed, and the stability properties and possible generalizations are commented on. As supplementary material to this paper we make available numerical data files for the sample of reference solutions discussed, for public use (see stacks.iop.org/cqg/32/144001/mmedia).

[]

https://arxiv.org/pdf/1501.04319.pdf

2015A&ARv..23....1B

Cosmic X-ray surveys of distant active galaxies. The demographics, physics, and ecology of growing supermassive black holes

2015-01-01

['surveys', 'cosmology observations', 'galaxies active', 'galaxies nuclei', 'galaxies seyfert', 'galaxies quasars', 'galaxies evolution', 'black hole physics', '-', '-', '-']

[]

We review results from cosmic X-ray surveys of active galactic nuclei (AGNs) over the past years that have dramatically improved our understanding of growing supermassive black holes in the distant universe. First, we discuss the utility of such surveys for AGN investigations and the capabilities of the missions making these surveys, emphasizing Chandra, XMM-Newton, and NuSTAR. Second, we briefly describe the main cosmic X-ray surveys, the essential roles of complementary multiwavelength data, and how AGNs are selected from these surveys. We then review key results from these surveys on the AGN population and its evolution ("demographics"), the physical processes operating in AGNs ("physics"), and the interactions between AGNs and their environments ("ecology"). We conclude by describing some significant unresolved questions and prospects for advancing the field.

[]

https://arxiv.org/pdf/1501.01982.pdf

2018MNRAS.474L..81L

Formation of precessing jets by tilted black hole discs in 3D general relativistic MHD simulations

2018-01-01

['accretion', 'accretion disks', 'black hole physics', 'mhd', 'methods numerical', 'galaxies jets', '-', '-', '-']

[]

Gas falling into a black hole (BH) from large distances is unaware of BH spin direction, and misalignment between the accretion disc and BH spin is expected to be common. However, the physics of tilted discs (e.g. angular momentum transport and jet formation) is poorly understood. Using our new GPU-accelerated code H-AMR, we performed 3D general relativistic magnetohydrodynamic simulations of tilted thick accretion discs around rapidly spinning BHs, at the highest resolution to date. We explored the limit where disc thermal pressure dominates magnetic pressure, and showed for the first time that, for different magnetic field strengths on the BH, these flows launch magnetized relativistic jets propagating along the rotation axis of the tilted disc (rather than of the BH). If strong large-scale magnetic flux reaches the BH, it bends the inner few gravitational radii of the disc and jets into partial alignment with the BH spin. On longer time-scales, the simulated disc-jet system as a whole undergoes Lense-Thirring precession and approaches alignment, demonstrating for the first time that jets can be used as probes of disc precession. When the disc turbulence is well resolved, our isolated discs spread out, causing both the alignment and precession to slow down.

[]

https://arxiv.org/pdf/1707.06619.pdf

2017JCAP...09..037R

Gravitational waves from primordial black hole mergers

2017-01-01

['-', '-']

[]

We study the production of primordial black hole (PBH) binaries and the resulting merger rate, accounting for an extended PBH mass function and the possibility of a clustered spatial distribution. Under the hypothesis that the gravitational wave events observed by LIGO were caused by PBH mergers, we show that it is possible to satisfy all present constraints on the PBH abundance, and find the viable parameter range for the lognormal PBH mass function. The non-observation of a gravitational wave background allows us to derive constraints on the fraction of dark matter in PBHs, which are stronger than any other current constraint in the PBH mass range 0.5-30M<SUB>solar</SUB>. We show that the predicted gravitational wave background can be observed by the coming runs of LIGO, and its non-observation would indicate that the observed events are not of primordial origin. As the PBH mergers convert matter into radiation, they may have interesting cosmological implications, for example in the context of relieving the tension between high and low redshift measurements of the Hubble constant. However, we find that these effects are suppressed as, after recombination, no more that 1% of dark matter can be converted into gravitational waves.

[]

https://arxiv.org/pdf/1707.01480.pdf

1995PhRvD..51..632C

Statistical mechanics of the (2+1)-dimensional black hole

1995-01-01

['-', '-', '-', '-', '-', '-', '-']

[]

The presence of a horizon breaks the gauge invariance of (2+1)-dimensional general relativity, leading to the appearance of new physical states at the horizon. I show that the entropy of the (2+1)-dimensional black hole can be obtained as the logarithm of the number of these microscopic states.

[]

https://arxiv.org/pdf/gr-qc/9409052.pdf

1996NuPhB.475..679M

D-branes and fat black holes

1996-01-01

['-']

[]

The application of D-brane methods to large black holes whose Schwarzschild radius is larger than the compactification scale is problematic. Callan and Maldacena have suggested that despite apparent problems of strong interactions when the number of branes becomes large, the open string degrees of freedom may remain very dilute due to the growth of the horizon area which they claim grows more rapidly than the average number of open strings. Such a picture of a dilute weakly coupled string system conflicts with the picture of a dense string soup that saturates the bound of one string per Planck area. A more careful analysis shows that Callan and Maldacena were not fully consistent in their estimates. In the form that their model was studied it can not be used to extrapolate to large mass without being in conflict with the Hawking-Bekenstein entropy formula. A somewhat modified model can reproduce the correct entropy formula. In this "improved model" the number of string bits on the horizon scales like the entropy in agreement with earlier speculations of Susskind.

[]

https://arxiv.org/pdf/hep-th/9604042.pdf

2009PhRvD..80b4003C

Topological black holes in Hořava-Lifshitz gravity

2009-01-01

['-', '-', '-', '-']

[]

We find topological (charged) black holes whose horizon has an arbitrary constant scalar curvature 2k in Hořava-Lifshitz theory. Without loss of generality, one may take k=1, 0, and -1. The black hole solution is asymptotically anti-de Sitter with a nonstandard asymptotic behavior. Using the Hamiltonian approach, we define a finite mass associated with the solution. We discuss the thermodynamics of the topological black holes and find that the black hole entropy has a logarithmic term in addition to an area term. We find a duality in Hawking temperature between topological black holes in Hořava-Lifshitz theory and Einstein’s general relativity: the temperature behaviors of black holes with k=1, 0, and -1 in Hořava-Lifshitz theory are, respectively, dual to those of topological black holes with k=-1, 0, and 1 in Einstein’s general relativity. The topological black holes in Hořava-Lifshitz theory are thermodynamically stable.

[]

https://arxiv.org/pdf/0904.3670.pdf

2014PhRvD..90l4045B

Regular black holes with a nonlinear electrodynamics source

2014-01-01

['-', '-', '-', '-', '-', '-', '-', '-']

[]

We construct several charged regular black hole metrics employing mass distribution functions which are inspired by continuous probability distributions. Some of these metrics satisfy the weak energy condition and asymptotically behave as the Reissner-Nordström black hole. In each case, the source to the Einstein equations corresponds to a nonlinear electrodynamics model, which in the weak field limit becomes the Maxwell theory (compatible with the Maxwell weak field limit or approximation). Furthermore, we include other regular black hole solutions that satisfy the weak energy condition, and some of them correspond to the Maxwell theory in the weak field limit.

[]

https://arxiv.org/pdf/1408.0306.pdf

1996PhRvD..53..584C

Dyonic BPS saturated black holes of heterotic string on a six-torus

1996-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

Within effective heterotic superstring theory compactified on a six-torus we derive minimum energy (supersymmetric), static, spherically symmetric solutions, which are manifestly invariant under the target space O(6,22) and the strong-weak coupling SL(2) duality symmetries with 28 electric and 28 magnetic charges subject to one constraint. The class of solutions with a constant axion corresponds to dyonic configurations subject to two charge constraints, with purely electric (or purely magnetic) and dyonic configurations preserving 1/2 and 1/4 of N=4 supersymmetry, respectively. General dyonic configurations in this class have a space-time of extreme Reissner-Nordström black holes while configurations with more constrained charges have a null or a naked singularity.

[]

https://arxiv.org/pdf/hep-th/9507090.pdf

2003ApJ...583..124S

The Black Hole-Bulge Relationship in Quasars

2003-01-01

['black hole physics', 'galaxies active', 'galaxies quasars', 'astrophysics']

[]

We use quasi-stellar object (QSO) emission-line widths to examine the M<SUB>BH</SUB>-σ<SUB>*</SUB> relationship as a function of redshift and to extend the relationship to larger masses. Supermassive black holes in galactic nuclei are closely related to the bulge of the host galaxy. The mass of the black hole M<SUB>BH</SUB> increases with the bulge luminosity and with the velocity dispersion of the bulge stars, σ<SUB>*</SUB>. An important clue to the origin of this correlation would be an observational determination of the evolution, if any, in the M<SUB>BH</SUB>-σ<SUB>*</SUB> relationship as a function of cosmic time. The high luminosity of QSOs affords the potential for studies at large redshifts. We derive black hole masses from the continuum luminosity and the width of the broad Hβ line and σ<SUB>*</SUB> from the width of the narrow [O III] lines. We find that radio-quiet QSOs conform to the established M<SUB>BH</SUB>-σ<SUB>*</SUB> relationship up to values of M<SUB>BH</SUB>~10<SUP>10</SUP> M<SUB>solar</SUB>, with no discernible change in the relationship out to redshifts of z~3. These results are consistent with the idea that the growth of supermassive black holes and massive bulges occurred simultaneously.

[]

https://arxiv.org/pdf/astro-ph/0210050.pdf

2001JMP....42.2961M

Strings in AdS<SUB>3</SUB> and the SL(2,R) WZW model. II: Euclidean black hole

2001-01-01

['-', '-', '-', '-', '-', '-', '-', '-', 'black hole physics', '-', '-', 'elementary particles', '-']

[]

We consider the one-loop partition function for Euclidean BTZ black hole back-grounds or equivalently thermal AdS3 backgrounds which are quotients of H3 (Euclidean AdS3). The one-loop partition function is modular invariant and we can read off the spectrum which is consistent to that found in hep-th/0001053. We see long strings and discrete states in agreement with the expectations.

[]

https://arxiv.org/pdf/hep-th/0005183.pdf

2005CQGra..22.1405M

Computations of primordial black-hole formation

2005-01-01

['-', 'astrophysics']

[]

Results are presented from general relativistic numerical computations of primordial black-hole formation during the radiation-dominated era of the universe. Growing-mode perturbations are specified within the linear regime and their subsequent evolution is followed as they become nonlinear. We use a spherically symmetric Lagrangian code and study both super-critical perturbations, which go on to produce black holes, and sub-critical perturbations, for which the overdensity eventually disperses into the background medium. For super-critical perturbations, we confirm the results of previous work concerning scaling laws but note that the threshold amplitude for a perturbation to lead to black-hole formation is substantially reduced when the initial conditions are taken to represent purely growing modes. For sub-critical cases, where an initial collapse is followed by a subsequent re-expansion, strong compressions and rarefactions are seen for perturbation amplitudes near to the threshold. We have also investigated the effect of including a significant component of vacuum energy and have calculated the resulting changes in the threshold and in the slope of the scaling law.

[]

https://arxiv.org/pdf/gr-qc/0412063.pdf

2006ApJ...637..937O

Binary Mergers and Growth of Black Holes in Dense Star Clusters

2006-01-01

['black hole physics', 'galaxies kinematics and dynamics', 'galaxies star clusters', 'gravitational waves', 'astrophysics']

[]

We model the dynamical evolution of primordial black holes (BHs) in dense star clusters using a simplified treatment of stellar dynamics in which the BHs are assumed to remain concentrated in an inner core, completely decoupled from the background stars. Dynamical interactions involving BH binaries are computed exactly and are generated according to a Monte Carlo prescription. Recoil and ejections lead to complete evaporation of the BH core on a timescale ~10<SUP>9</SUP> yr for typical globular cluster parameters. Orbital decay driven by gravitational radiation can make binaries merge, and, in some cases, successive mergers can lead to significant BH growth. Our highly simplified treatment of the cluster dynamics allows us to study a large number of models and to compute statistical distributions of outcomes, such as the probability of massive BH growth and retention in a cluster. We find that, in most models, there is a significant probability (~20%-80%) of BH growth with final masses &gt;~100 M<SUB>solar</SUB>. In one case, a BH formed with mass ~620 M<SUB>solar</SUB>. However, if the typical merger recoil speed (due to asymmetric emission of gravitational radiation) significantly exceeds the cluster escape speed, no growth ever occurs. Independent of the recoil speed, we find that BH-BH mergers enhanced by dynamical interactions in cluster cores present an important source of gravitational waves for ground-based laser interferometers. Under optimistic conditions, the total rate of detections by Advanced LIGO could be as high as a few tens of events per year from inspiraling BHs from clusters.

[]

https://arxiv.org/pdf/astro-ph/0508224.pdf

2015PASP..127...67B

The AGN Black Hole Mass Database

2015-01-01

['-']

[]

The AGN Black Hole Mass Database is a compilation of all published spectroscopic reverberation-mapping studies of active galaxies. We have created a public web interface, where users may get the most up-to-date black hole masses from reverberation mapping for any particular active galactic nucleus (AGN), as well as obtain the individual measurements upon which the masses are based and the appropriate references. While the database currently focuses on the measurements necessary for black hole mass determinations, we also plan to expand it in the future to include additional useful information, such as host-galaxy characteristics. New reverberation mapping results will also be incorporated into the database as they are published in peer-refereed journals.

[]

https://arxiv.org/pdf/1411.2596.pdf

2018PhRvD..97j3014S

Eccentric black hole mergers forming in globular clusters

2018-01-01

['-']

[]

We derive the probability for a newly formed binary black hole (BBH) to undergo an eccentric gravitational wave (GW) merger during binary-single interactions inside a stellar cluster. By integrating over the hardening interactions such a BBH must undergo before ejection, we find that the observable rate of BBH mergers with eccentricity &gt;0.1 at 10 Hz relative to the rate of circular mergers can be as high as ∼5 % for a typical globular cluster (GC). This further suggests that BBH mergers forming through GW captures in binary-single interactions, eccentric or not, are likely to constitute ∼10 % of the total BBH merger rate from GCs. Such GW capture mergers can only be probed with an N -body code that includes general relativistic corrections, which explains why recent Newtonian cluster studies have not been able to resolve this population. Finally, we show that the relative rate of eccentric BBH mergers depends on the compactness of their host cluster, suggesting that an observed eccentricity distribution can be used to probe the origin of BBH mergers.

[]

https://arxiv.org/pdf/1711.07452.pdf

2010A&A...518L..42V

Black hole accretion and star formation as drivers of gas excitation and chemistry in Markarian 231

2010-01-01

['galaxies', 'galaxies active', 'galaxies intergalactic medium', 'galaxies nuclei', 'galaxies starburst', 'astronomy infrared', '-', '-']

[]

We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J = 5-4 through J = 13-12, 7 rotational lines of H<SUB>2</SUB>O, 3 of OH<SUP>+</SUP> and one line each of H<SUB>2</SUB>O<SUP>+</SUP>, CH<SUP>+</SUP>, and HF. We find that the excitation of the CO rotational levels up to J = 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J = 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J = 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH<SUP>+</SUP> and H<SUB>2</SUB>O<SUP>+</SUP> lines reveals the signature of X-ray driven excitation and chemistry in this region.

[]

https://arxiv.org/pdf/1005.2877.pdf

1997ApJ...476...49N

Global Structure and Dynamics of Advection-dominated Accretion Flows around Black Holes

1997-01-01

['accretion', 'accretion disks', 'stars binaries close', 'black hole physics', 'galaxies active', 'hydrodynamics', 'astrophysics']

[]

We present global solutions that describe advection-dominated accretion flows around black holes. The solutions are obtained by solving numerically a set of coupled ordinary differential equations corresponding to a steady axisymmetric height-integrated flow. The solutions satisfy consistent boundary conditions at both ends. On the inside, the flow passes through a sonic point and falls supersonically into the black hole with a zero-torque condition at the horizon. On the outside, the flow attaches to a normal thin accretion disk. <P />We obtain consistent transonic solutions for a wide range of values of the viscosity parameter α, from 0.001 to 0.3. We do not find any need for shocks in our solutions, and we disagree with previous claims that viscous accretion flows with low values of α must have shocks. <P />We compare the exact global solutions of this paper with a local self-similar solution that has been studied in the past. Although the self-similar solution makes significant errors close to the boundaries, we find that it provides nevertheless a reasonable description of the overall properties of the flow. We compare also two different forms of viscosity: one is based on a diffusion prescription, while the other takes the shear stress to be simply proportional to the pressure. The results with the two prescriptions are similar. <P />We see a qualitative difference between solutions with low values of the visocity parameter, α &lt;~ 0.01, and those with large values, α &gt;~ 0.01. The solutions with low α have their sonic transitions occurring close to the radius of the marginally bound orbit. These flows are characterized by regions of super-Keplerian rotation and have pressure maxima outside the sonic point. The solutions are similar in many respects to the hydrostatic thick tori developed previously as models of active galactic nuclei. In contrast, the solutions with large α have sonic transitions farther out, close to, or beyond the marginally stable orbit and have no super-Keplerian rotation or pressure maxima. We believe these flows will be nearly quasi-spherical down to the sonic radius and will not have empty funnels along the rotation axis. The large-α solutions are more likely to be representative of real systems, since most observations of astrophysical systems are best fit, within the context of advection-dominated theories, with values of α &gt;~ 0.1.

[]

https://arxiv.org/pdf/astro-ph/9607019.pdf

2001MNRAS.327..199M

The black hole masses of Seyfert galaxies and quasars

2001-01-01

['galaxies active', 'galaxies nuclei', 'galaxies quasars', 'galaxies seyfert', 'astrophysics']

[]

The central black hole masses of a sample of 30 luminous quasars are estimated using Hβ full width half-maximum (FWHM) measurements from a combination of new and previously published nuclear spectra. The quasar black hole mass estimates are combined with reverberation-mapping measurements for a sample of Seyfert galaxies in order to study active galatic nucleus (AGN) black hole masses over a wide range in nuclear luminosity. The link between bulge luminosity and black hole mass is investigated using two-dimensional disc/bulge decompositions of the host galaxy images, the vast majority of which are high-resolution Hubble Space Telescope (HST) observations. It is found that black hole mass and bulge luminosity are well correlated and follow a relation consistent with that expected if black hole and bulge mass are directly proportional. Contrary to the recent results of Wandel, no evidence that Seyfert galaxies follow a different M<SUB>bh</SUB>-M<SUB>bulge</SUB> relation to quasars is found. However, the black hole mass distributions of the radio-loud and radio-quiet quasar subsamples are found to be significantly different, with the median black hole mass of the radio-loud quasars a factor of three larger than their radio-quiet counterparts. Finally, utilizing the elliptical galaxy fundamental plane to provide stellar velocity dispersion estimates, a comparison is performed between the virial Hβ black hole mass estimates and those of the M<SUB>bh</SUB>-σ correlations of Gebhardt et al. and Merritt &amp; Ferrarese. With the disc geometry of the broad-line region adopted in this paper, the virial Hβ black hole masses indicate that the correct normalization of the black hole versus bulge mass relation is M<SUB>bh</SUB>~=0.0025M<SUB>bulge</SUB>, while the standard assumption of purely random broad-line velocities leads to M<SUB>bh</SUB>~=0.0008M<SUB>bulge</SUB>. The normalization of M<SUB>bh</SUB>~=0.0025M<SUB>bulge</SUB> provided by the disc model is in remarkably good agreement with that inferred for our quasar sample using the (completely independent) M<SUB>bh</SUB>-σ correlations.

[]

https://arxiv.org/pdf/astro-ph/0009406.pdf

2000hep.th....5003D

A Black Hole Farey Tail

2000-01-01

['-']

[]

We derive an exact expression for the Fourier coefficients of elliptic genera of Calabi-Yau manifolds. When applied to k-fold symmetric products of K3 surfaces the expression is well-suited to studying the AdS/CFT correspondence on AdS3 x S3. The expression also elucidates an SL(2,Z) invariant phase diagram for the D1/D5 system involving deconfining transitions in the limit as k goes to infinity.

[]

https://arxiv.org/pdf/hep-th/0005003.pdf

2005ApJ...634.1202R

Mergers of Neutron Star-Black Hole Binaries with Small Mass Ratios: Nucleosynthesis, Gamma-Ray Bursts, and Electromagnetic Transients

2005-01-01

['black hole physics', 'gamma rays', 'hydrodynamics', 'methods numerical', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', 'astrophysics']

[]

We discuss simulations of the coalescence of black hole-neutron star binary systems with black hole masses between 14 and 20 M<SUB>solar</SUB>. The calculations use a three-dimensional smoothed particle hydrodynamics code, a temperature-dependent, nuclear equation of state, and a multiflavor neutrino scheme. General relativistic effects are mimicked using the Paczyński-Wiita pseudo-potential and gravitational radiation reaction forces. Unlike previous, purely Newtonian calculations, in none of the explored cases does episodic mass transfer occur. The neutron star is always completely disrupted after most of its mass has been transferred directly into the hole. For black hole masses between 14 and 16 M<SUB>solar</SUB> an accretion disk forms; large parts of it, however, are inside the last stable orbit and therefore falling with large radial velocities into the hole. These disks are (opposite to the neutron star merger case) thin and-except for a spiral shock-essentially cold. For higher mass black holes (M<SUB>BH</SUB>&gt;=18 M<SUB>solar</SUB>) almost the entire neutron star disappears in the hole without forming an accretion disk. In these cases the surviving material is spun up by tidal torques and ejected as a half-ring of neutron-rich matter. None of the investigated systems is a promising gamma-ray burst (GRB) central engine. We find between 0.01 and 0.2 M<SUB>solar</SUB> of the neutron star to be dynamically ejected. Like in a Type Ia supernova, the radioactive decay of this material powers a light curve with a peak luminosity of a few times 10<SUP>44</SUP> ergs s<SUP>-1</SUP>. The maximum is reached about 3 days after the coalescence and is mainly visible in the optical/near-infrared band. The coalescence itself may produce a precursor pulse with a thermal spectrum of ~10 ms duration.

[]

https://arxiv.org/pdf/astro-ph/0508138.pdf

2014PhRvD..90f4041A

Generating rotating regular black hole solutions without complexification

2014-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

We drop the complexification procedure from the Newman-Janis algorithm and introduce more physical arguments and symmetry properties, and we show how one can generate regular and singular rotating black hole and non-black-hole solutions in Boyer-Lindquist coordinates. We focus on generic rotating regular black holes and show that they are regular on the Kerr-like ring, but physical entities are undefined there. We show that rotating regular black holes have much smaller electric charges, and, with increasing charge, they turn into regular non-black-hole solutions well before their Kerr-Newman counterparts become naked singularities. No causality violations occur in the region inside a rotating regular black hole. The separability of the Hamilton-Jacobi equation for neutral particles is also carried out in the generic case, and the innermost boundaries of circular orbits for particles are briefly discussed. Other, but special, properties pertaining to the rotating regular counterpart of the Ayón-Beato-García regular static black hole are also investigated.

[]

https://arxiv.org/pdf/1405.2569.pdf

2013ApJ...770...86W

The M87 Black Hole Mass from Gas-dynamical Models of Space Telescope Imaging Spectrograph Observations

2013-01-01

['galaxies active', 'galaxies', 'galaxies kinematics and dynamics', 'galaxies nuclei', '-']

[]

The supermassive black hole of M87 is one of the most massive black holes known and has been the subject of several stellar and gas-dynamical mass measurements; however, the most recent revision to the stellar-dynamical black hole mass measurement is a factor of about two larger than the previous gas-dynamical determinations. Here, we apply comprehensive gas-dynamical models that include the propagation of emission-line profiles through the telescope and spectrograph optics to new Space Telescope Imaging Spectrograph observations from the Hubble Space Telescope. Unlike the previous gas-dynamical studies of M87, we map out the complete kinematic structure of the emission-line disk within ~40 pc from the nucleus, and find that a small amount of velocity dispersion internal to the gas disk is required to match the observed line widths. We examine a scenario in which the intrinsic velocity dispersion provides dynamical support to the disk, and determine that the inferred black hole mass increases by only 6%. Incorporating this effect into the error budget, we ultimately measure a mass of M_{BH} = (3.5^{+0.9}_{-0.7}) \times 10^9\, M_\odot (68% confidence). Our gas-dynamical black hole mass continues to differ from the most recent stellar-dynamical mass by a factor of two, underscoring the need for carrying out more cross-checks between the two main black hole mass measurement methods. <P />Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-12162.

[]

https://arxiv.org/pdf/1304.7273.pdf

2015PhRvL.115k1302W

Insight into the Microscopic Structure of an AdS Black Hole from a Thermodynamical Phase Transition

2015-01-01

['-', '-', '-', '-', '-', 'thermodynamics', '-', '-']

[]

Comparing with an ordinary thermodynamic system, we investigate the possible microscopic structure of a charged anti-de Sitter black hole completely from the thermodynamic viewpoint. The number density of the black hole molecules is introduced to measure the microscopic degrees of freedom of the black hole. We found that the number density suffers a sudden change accompanied by a latent heat when the black hole system crosses the small-large black hole coexistence curve, while when the system passes the critical point, it encounters a second-order phase transition with a vanishing latent heat due to the continuous change of the number density. Moreover, the thermodynamic scalar curvature suggests that there is a weak attractive interaction between two black hole molecules. These phenomena might cast new insight into the underlying microscopic structure of a charged anti-de Sitter black hole.

[]

https://arxiv.org/pdf/1502.00386.pdf

2003ApJ...587L..15W

A 3×10<SUP>9</SUP> M<SUB>solar</SUB> Black Hole in the Quasar SDSS J1148+5251 at z=6.41

2003-01-01

['galaxies formation', 'galaxies quasars', 'galaxies quasars', 'astrophysics']

[]

We present near-infrared H- and K-band spectra of the z=6.41 quasar SDSS J114816.64+525150.3. The spectrum reveals a broad Mg II λ2799 emission line with an FWHM of 6000 km s<SUP>-1</SUP>. From the peak wavelength of this emission line, we obtain a more accurate redshift than is possible from the published optical spectrum and determine a redshift of z=6.41+/-0.01. If the true peak of the Lyα emission is at the same redshift, then a large fraction of the flux blueward of the peak is absorbed. The equivalent width of the Mg II emission line is similar to that of lower redshift quasars, suggesting that the UV continuum is not dominated by a beamed component. Making basic assumptions about the line-emitting gas, we derive a mass estimate of 3×10<SUP>9</SUP> M<SUB>solar</SUB> for the central black hole in this quasar. The very high luminosity of the quasar shows that it is accreting at the maximal allowable rate for a black hole of this mass, adopting the Eddington limit criterion.

[]

https://arxiv.org/pdf/astro-ph/0303062.pdf

2019JHEP...09..056G

Scattering of spinning black holes from exponentiated soft factors

2019-01-01

['scattering', 'black hole physics', '-', '-']

[]

We provide evidence that the classical scattering of two spinning black holes is controlled by the soft expansion of exchanged gravitons. We show how an exponentiation of Cachazo-Strominger soft factors, acting on massive higher-spin amplitudes, can be used to find spin contributions to the aligned-spin scattering angle, conjecturally extending previously known results to higher orders in spin at one-loop order. The extraction of the classical limit is accomplished via the on-shell leading-singularity method and using massive spinor-helicity variables. The three-point amplitude for arbitrary-spin massive particles minimally coupled to gravity is expressed in an exponential form, and in the infinite-spin limit it matches the effective stress-energy tensor of the linearized Kerr solution. A four-point gravitational Compton amplitude is obtained from an extrapolated soft theorem, equivalent to gluing two exponential three-point amplitudes, and becomes itself an exponential operator. The construction uses these amplitudes to: 1) recover the known tree-level scattering angle at all orders in spin, 2) recover the known one-loop linear-in-spin interaction, 3) match a previous conjectural expression for the one-loop scattering angle at quadratic order in spin, 4) propose new one-loop results through quartic order in spin. These connections link the computation of higher-multipole interactions to the study of deeper orders in the soft expansion.

[]

https://arxiv.org/pdf/1812.06895.pdf

1992NuPhB.380..447H

Black holes as elementary particles

1992-01-01

['-']

[]

It is argued that the qualitative features of black holes, regarded as quantum-mechanical objects, depend both on the parameters of the hole and on the microscopic theory in which it is embedded. A thermal description is inadequate for external holes. In particular, extreme holes of the charged dilaton family can have entropy but nonzero, and even (for a &gt; 1) formally infinite, temperature. The existence of a tendency to radiate at the extreme, which threatens to overthrow any attempt to identify the entropy as available internal states and also to expose a naked singularity, is at first quite disturbing. However, by analyzing the perturbations around the extreme holes we show that these holes are protected by mass gaps, or, alternatively, potential barriers, which removes them from thermal contact with the external world. We suggest that the behavior of these extreme-dilation black holes, which from the point of view of traditional black-hole theory seems quite bizarre, can reasonably be interpreted as the holes doing their best to behave like normal elementary particles. The a &lt; 1 holes behave qualitatively as extended objects.

[]

https://arxiv.org/pdf/hep-th/9202014.pdf

2013A&A...558A..43S

The nature of LINER galaxies:. Ubiquitous hot old stars and rare accreting black holes

2013-01-01

['galaxies active', 'galaxies intergalactic medium', 'galaxies nuclei', 'stars agb and post agb', '-', '-']

[]

Context. Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus, AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. <BR /> Aims: Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN. <BR /> Methods: Essential for this analysis is a proper extraction of emission lines, especially weak lines, such as Balmer Hβ lines, which are superposed on an absorption trough. To accomplish this, we use the GANDALF code, which simultaneously fits the underlying stellar continuum and emission lines. <BR /> Results: For 48 galaxies with LINER-like emission, we show that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. <BR /> Conclusions: The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with the gas present and with stars older than ~1 Gyr unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.

[]

https://arxiv.org/pdf/1308.4271.pdf

2009ApJ...694..302D

Formation of the First Nuclear Clusters and Massive Black Holes at High Redshift

2009-01-01

['black hole physics', 'instabilities', 'stars kinematics and dynamics', 'galaxies nuclei', 'galaxies formation', 'astrophysics']

[]

We present a model for the formation of massive black holes (~1000 M <SUB>sun</SUB>) due to stellar-dynamical processes in the first stellar clusters formed at early cosmic times (z ~ 10-20). These black holes are likely candidates as seeds for the supermassive black holes detected in quasars and nearby quiescent galaxies. The high redshift black hole seeds form as a result of multiple successive instabilities that occur in low metallicity (Z ~ 10<SUP>-5</SUP> Z <SUB>sun</SUB>) protogalaxies. We focus on relatively massive halos at high redshift (T <SUB>vir</SUB> &gt; 10<SUP>4</SUP> K, z gsim 10) after the very first stars in the universe have completed their evolution. This set of assumptions ensures that (1) atomic hydrogen cooling can contribute to the gas cooling process, (2) a UV field has been created by the first stars, and (3) the gas inside the halo has been mildly polluted by the first metals. The second condition implies that at low density H <SUB>2</SUB> is dissociated and does not contribute to cooling. The third condition sets a minimum threshold density for fragmentation, so that stars form efficiently only in the very inner core of the protogalaxy. Within this core, very compact stellar clusters form. The typical star cluster masses are of order 10<SUP>5</SUP> M <SUB>sun</SUB> and the typical half mass radii ~1 pc. A large fraction of these very dense clusters undergoes core collapse before stars are able to complete stellar evolution. Runaway star-star collisions eventually lead to the formation of a very massive star, leaving behind a massive black hole remnant. Clusters unstable to runaway collisions are always the first, less massive ones that form. As the metallicity of the universe increases, the critical density for fragmentation decreases and stars start to form in the entire protogalactic disk so that (1) accretion of gas in the center is no longer efficient and (2) the core collapse timescale increases. Typically, a fraction ~0.05 of protogalaxies at z ~ 10-20 form black hole seeds, with masses ~1000-2000 M <SUB>sun</SUB>, leading to a mass density in seeds of a few sime10<SUP>2</SUP> M <SUB>sun</SUB>/Mpc<SUP>-3</SUP>. This density allows enough room for black hole growth by accretion during the quasar epoch.

[]

https://arxiv.org/pdf/0810.1057.pdf

2008arXiv0802.0330A

Spherical black holes with regular center: a review of existing models including a recent realization with Gaussian sources

2008-01-01

['-']

[]

We review, in a historical perspective, some results about black hole spacetimes with a regular center. We then see how their properties are realized in a specific solution that recently appeared; in particular we analyze in detail the (necessary) violation of the strong energy condition.

[]

https://arxiv.org/pdf/0802.0330.pdf

2017PhRvD..96f3503M

Primordial black holes and slow-roll violation

2017-01-01

['-', '-']

[]

For primordial black holes (PBH) to be the dark matter in single-field inflation, the slow-roll approximation must be violated by at least O (1 ) in order to enhance the curvature power spectrum within the required number of e -folds between cosmic microwave background scales and PBH mass scales. Power spectrum predictions which rely on the inflaton remaining on the slow-roll attractor can fail dramatically leading to qualitatively incorrect conclusions in models like an inflection potential and misestimate the mass scale in a running mass model. We show that an optimized temporal evaluation of the Hubble slow-roll parameters to second order remains a good description for a wide range of PBH formation models where up to a 1 0<SUP>7</SUP> amplification of power occurs in 10 e -folds or more.

[]

https://arxiv.org/pdf/1706.06784.pdf

2000ApJ...528..161A

Magnetic Stress at the Marginally Stable Orbit: Altered Disk Structure, Radiation, and Black Hole Spin Evolution

2000-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxies active', 'line profiles', 'polarization', 'relativity', 'accretion', 'accretion disks', 'black hole physics', 'galaxies active', 'line profiles', 'polarization', 'relativity', 'astrophysics']

[]

Magnetic connections to the plunging region can exert stresses on the inner edge of an accretion disk around a black hole. We recompute the relativistic corrections to the thin-disk dynamics equations when these stresses take the form of a time-steady torque on the inner edge of the disk. The additional dissipation associated with these stresses is concentrated relatively close outside the marginally stable orbit, scaling as r<SUP>-7/2</SUP> at large radius. As a result of these additional stresses, spin-up of the central black hole is retarded; the maximum spin-equilibrium accretion efficiency is 36% and occurs at a/M=0.94 the disk spectrum is extended toward higher frequencies; line profiles (such as Fe Kα) are broadened if the line emissivity scales with local flux; limb brightening, especially at the higher frequencies, is enhanced; and the returning radiation fraction is substantially increased, up to 58%. This last effect creates possible explanations for both synchronized continuum fluctuations in active galactic nuclei and polarization rises shortward of the Lyman edge in quasars. We show that no matter what additional stresses occur, when a/M&lt;0.36, the second law of black hole dynamics sets an absolute upper bound on the accretion efficiency.

[]

https://arxiv.org/pdf/astro-ph/9908049.pdf

1996PhRvD..54.3840L

Rotating charged black strings and three-dimensional black holes

1996-01-01

['-', '-', '-', '-', '-', '-']

[]

Einstein-Maxwell equations with a cosmological constant are analyzed in a four-dimensional stationary spacetime admitting in addition a two-dimensional group G<SUB>2</SUB> of spatial isometries. We find charged rotating black string solutions. For open black strings the mass (M), angular momentum (J), and charge (Q) line densities can be defined using the Hamiltonian formalism of Brown and York. It is shown through dimensional reduction that M, J, and Q are, respectively, the mass, angular momentum, and charge of a related three-dimensional black hole. For closed black strings one can define the total mass, charge, and angular momentum of the solution. These closed black string solutions have a flat torus topology. The black string solutions are classified according to the mass, charge, and angular momentum parameters. The causal structure is studied and some Penrose diagrams are shown. There are similarities between the charged rotating black string and the Kerr-Newman spacetime. The solution has Cauchy and event horizons, ergosphere, timelike singularities, closed timelike curves, and extremal cases. Both the similarities and differences of these black strings and Kerr-Newman black holes are explored. We comment on the implications these solutions might have on the hoop conjecture.

[]

https://arxiv.org/pdf/hep-th/9511188.pdf

2003PhRvD..67h4027M

Perturbative approach to an orbital evolution around a supermassive black hole

2003-01-01

['-', '-', 'waves', '-', 'perturbation theory', '-', '-']

[]

A charge-free, point particle of infinitesimal mass orbiting a Kerr black hole is known to move along a geodesic. When the particle has a finite mass or charge, it emits radiation which carries away orbital energy and angular momentum, and the orbit deviates from a geodesic. In this paper we assume that the deviation is small and show that the half-advanced minus half-retarded field surprisingly provides the correct radiation reaction force, in a time-averaged sense, and determines the orbit of the particle.

[]

https://arxiv.org/pdf/gr-qc/0302075.pdf

2017ApJ...841...77A

Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

2017-01-01

['stars black holes', '-', '-', '-']

[]

We consider the formation of binary black hole (BH) mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a BH binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov-Kozai cycles) with stellar evolution. After a BH triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. Most BH mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a BH merger rate in the range (0.3-1.3) Gpc<SUP>-3</SUP> yr<SUP>-1</SUP>, or up to ≈2.5 Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> if the BH orbital planes have initially random orientation. Finally, we show that BH mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ≈10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.

[]

https://arxiv.org/pdf/1703.06614.pdf

2017PhRvD..95l4046G

Are merging black holes born from stellar collapse or previous mergers?

2017-01-01

['-', '-']

[]

Advanced LIGO detectors at Hanford and Livingston made two confirmed and one marginal detection of binary black holes during their first observing run. The first event, GW150914, was from the merger of two black holes much heavier that those whose masses have been estimated so far, indicating a formation scenario that might differ from "ordinary" stellar evolution. One possibility is that these heavy black holes resulted from a previous merger. When the progenitors of a black hole binary merger result from previous mergers, they should (on average) merge later, be more massive, and have spin magnitudes clustered around a dimensionless spin ∼0.7 . Here we ask the following question: can gravitational-wave observations determine whether merging black holes were born from the collapse of massive stars ("first generation"), rather than being the end product of earlier mergers ("second generation")? We construct simple, observationally motivated populations of black hole binaries, and we use Bayesian model selection to show that measurements of the masses, luminosity distance (or redshift), and "effective spin" of black hole binaries can indeed distinguish between these different formation scenarios.

[]

https://arxiv.org/pdf/1703.06223.pdf

2017MNRAS.470.4739S

Very massive stars, pair-instability supernovae and intermediate-mass black holes with the sevn code

2017-01-01

['black hole physics', 'gravitational waves', 'methods numerical', 'stars luminosity function;mass function', 'stars novae;cataclysmic variables', '-', '-']

[]

Understanding the link between massive (≳30 M<SUB>⊙</SUB>) stellar black holes (BHs) and their progenitor stars is a crucial step to interpret observations of gravitational-wave events. In this paper, we discuss the final fate of very massive stars (VMSs), with zero-age main sequence (ZAMS) mass &gt;150 M<SUB>⊙</SUB>, accounting for pulsational pair-instability supernovae (PPISNe) and for pair-instability supernovae (PISNe). We describe an updated version of our population synthesis code sevn, in which we added stellar evolution tracks for VMSs with ZAMS mass up to 350 M<SUB>⊙</SUB> and we included analytical prescriptions for PPISNe and PISNe. We use the new version of sevn to study the BH mass spectrum at different metallicity Z, ranging from Z = 2.0 × 10<SUP>-4</SUP> to 2.0 × 10<SUP>-2</SUP>. The main effect of PPISNe and PISNe is to favour the formation of BHs in the mass range of the first gravitational-wave event (GW150914), while they prevent the formation of remnants with mass 60-120 M<SUB>⊙</SUB>. In particular, we find that PPISNe significantly enhance mass-loss of metal-poor (Z ≤ 2.0 × 10<SUP>-3</SUP>) stars with ZAMS mass 60 ≤ M<SUB>ZAMS</SUB>/ M<SUB>⊙</SUB> ≤ 125. In contrast, PISNe become effective only for moderately metal-poor (Z &lt; 8.0 × 10<SUP>-3</SUP>) VMSs. VMSs with m<SUB>ZAMS</SUB> ≳ 220 M<SUB>⊙</SUB> and Z &lt; 10<SUP>-3</SUP> do not undergo PISNe and form intermediate-mass BHs (with mass ≳200 M<SUB>⊙</SUB>) via direct collapse.

[]

https://arxiv.org/pdf/1706.06109.pdf

2004PThPS.155...99Z

Radiative Processes, Spectral States and Variability of Black-Hole Binaries

2004-01-01

['astrophysics']

[]

We review radiative processes responsible for X-ray emission in hard(low) and soft (high) spectral states of black-hole binaries. The main process in the hard state appears to be scattering of blackbody photons from a cold disk by thermal electrons in a hot inner flow, and any contribution from nonthermal synchrotron emission is at most small. In the soft states, blackbody disk emission dominates energetically, and its high-energy tail is due to scattering by hybrid, thermal/nonthermal electrons, probably in active regions above the disk surface. State transitions appear to correspond to a variable inner radius of the cold disk driven by changes of the accretion rate. The existence of two accretion solutions, hot and cold, in a range of the accretion rate leads to hysteresis in low-mass X-ray binaries.

[]

https://arxiv.org/pdf/astro-ph/0403683.pdf

1995NuPhB.440..421S

Black hole solutions in heterotic string theory on a torus

1995-01-01

['-', '-']

[]

We construct the general electrically charged, rotating black hole solution in the heterotic string theory compactified on a six-dimensional torus and study its classical properties. This black hole is characterized by its mass, angular momentum, and a 28-dimensional electric charge vector. We recover the axion-dilaton black holes and Kaluza-Klein black holes for special values of the charge vector. For a generic black hole of this kind, the 28-dimensional magnetic dipole moment vector is not proportional to the electric charge vector, and we need two different gyromagnetic ratios for specifying the relation between these two vectors. We also give an algorithm for constructing a 58 parameter rotating dyonic black hole solution in this theory, characterized by its mass, angular momentum, a 28-dimensional electric charge vector and a 28-dimensional magnetic charge vector. This is the most general asymptotically flat black hole solution in this theory consistent with the no-hair theorem.

[]

https://arxiv.org/pdf/hep-th/9411187.pdf

2008PhLB..665..277K

Charged fermions tunnelling from Kerr Newman black holes

2008-01-01

['black hole physics', '-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

We consider the tunnelling of charged spin 1/2 fermions from a Kerr-Newman black hole and demonstrate that the expected Hawking temperature is recovered. We discuss certain technical subtleties related to the obtention of this result.

[]

https://arxiv.org/pdf/0803.2246.pdf

2020PhRvD.102d4055O

Multipolar effective-one-body waveforms for precessing binary black holes: Construction and validation

2020-01-01

['-']

[]

As gravitational-wave detectors become more sensitive and broaden their frequency bandwidth, we will access a greater variety of signals emitted by compact binary systems, shedding light on their astrophysical origin and environment. A key physical effect that can distinguish among different formation scenarios is the misalignment of the spins with the orbital angular momentum, causing the spins and the binary's orbital plane to precess. To accurately model such precessing signals, especially when masses and spins vary in the wide astrophysical range, it is crucial to include multipoles beyond the dominant quadrupole. Here, we develop the first multipolar precessing waveform model in the effective-one-body (EOB) formalism for the entire coalescence stage (i.e., inspiral, merger and ringdown) of binary black holes: SEOBNRv4PHM. In the nonprecessing limit, the model reduces to SEOBNRv4HM, which was calibrated to numerical-relativity (NR) simulations, and waveforms from black-hole perturbation theory. We validate SEOBNRv4PHM by comparing it to the public catalog of 1405 precessing NR waveforms of the Simulating eXtreme Spacetimes (SXS) collaboration, and also to 118 SXS precessing NR waveforms, produced as part of this project, which span mass ratios 1-4 and (dimensionless) black-hole's spins up to 0.9. We stress that SEOBNRv4PHM is not calibrated to NR simulations in the precessing sector. We compute the unfaithfulness against the 1523 SXS precessing NR waveforms, and find that, for 94% (57%) of the cases, the maximum value, in the total mass range 20 -200 M<SUB>⊙</SUB>, is below 3% (1%). Those numbers change to 83% (20%) when using the inspiral-merger-ringdown, multipolar, precessing phenomenological model IMRPhenomPv3HM. We investigate the impact of such unfaithfulness values with two Bayesian, parameter-estimation studies on synthetic signals. We also compute the unfaithfulness between those waveform models as a function of the mass and spin parameters to identify in which part of the parameter space they differ the most. We validate them also against the multipolar, precessing NR surrogate model NRSur7dq4, and find that the SEOBNRv4PHM model outperforms IMRPhenomPv3HM.

[]

https://arxiv.org/pdf/2004.09442.pdf

2016PhRvD..94h4025Y

New method for shadow calculations: Application to parametrized axisymmetric black holes

2016-01-01

['-', '-']

[]

Collaborative international efforts under the name of the Event Horizon Telescope project, using sub-mm very long baseline interferometry, are soon expected to provide the first images of the shadow cast by the candidate supermassive black hole in our Galactic center, Sagittarius A*. Observations of this shadow would provide direct evidence of the existence of astrophysical black holes. Although it is expected that astrophysical black holes are described by the axisymmetric Kerr solution, there also exist many other black hole solutions, both in general relativity and in other theories of gravity, which cannot presently be ruled out. To this end, we present calculations of black hole shadow images from various metric theories of gravity as described by our recent work on a general parametrization of axisymmetric black holes [R. Konoplya, L. Rezzolla, and A. Zhidenko, Phys. Rev. D 93, 064015 (2016).]. An algorithm to perform general ray-tracing calculations for any metric theory of gravity is first outlined and then employed to demonstrate that even for extremal metric deformation parameters of various black hole spacetimes, this parametrization is both robust and rapidly convergent to the correct solution.

[]

https://arxiv.org/pdf/1607.05767.pdf

2000PhRvD..61h4004H

Evolution of circular, nonequatorial orbits of Kerr black holes due to gravitational-wave emission

2000-01-01

['-', '-', '-', 'waves', '-', 'perturbation theory', '-', '-', '-', 'astrophysics']

[]

A major focus of much current research in gravitation theory is on understanding how radiation reaction drives the evolution of a binary system, particularly in the extreme mass ratio limit. Such research is of direct relevance to gravitational-wave sources for space-based detectors (such as LISA). We present here a study of the radiative evolution of circular (i.e., constant Boyer-Lindquist coordinate radius), non-equatorial Kerr black hole orbits. Recent theorems have shown that, at least in an adiabatic evolution, such orbits evolve from one circular configuration into another, changing only their radius and inclination angle. This constrains the system's evolution in such a way that the change in its Carter constant can be deduced from knowledge of gravitational wave fluxes propagating to infinity and down the black hole's horizon. Thus, in this particular case, a local radiation reaction force is not needed. In accordance with post-Newtonian weak-field predictions, we find that inclined orbits radiatively evolve to larger inclination angles (although the post-Newtonian prediction overestimates the rate of this evolution in the strong field by a factor &lt;~3). We also find that the gravitational waveforms emitted by these orbits are rather complicated, particularly when the hole is rapidly spinning, as the radiation is influenced by many harmonics of the orbital frequencies.

[]

https://arxiv.org/pdf/gr-qc/9910091.pdf

2004ApJ...611..996T

Shapes and Positions of Black Hole Shadows in Accretion Disks and Spin Parameters of Black Holes

2004-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxies nuclei', 'astrophysics']

[]

Can we determine the spin parameter of a black hole by observing the black hole's shadow on an accretion disk? To answer this question, we make qualitative and quantitative analyses of the shape and position of the shadow cast by a rotating black hole on an optically thick accretion disk and its dependence on the angular momentum of the black hole. We consider two types of inner edges of accretion disks, an event horizon and a marginally stable orbit. We have found black hole shadows of quite similar sizes and shapes for very different black hole spin parameters and the same black hole mass. Thus, in practice it is difficult to determine the spin parameter of a black hole from the size and shape of its shadow on an accretion disk. On the other hand, a frame-dragging effect in the vicinity of a black hole causes a displacement of the shadow from the rotation axis of the black hole. The extent of the displacement largely depends on the black hole's spin parameter. However, it is difficult to determine the position of the rotation axis of a black hole observationally. So, we cannot practically use the displacement of the rotation axis of a black hole shadow to measure the spin parameter. We here introduce a bisector axis of black hole shadows that we call the ``shadow axis.'' We define this as the bisector perpendicular to a line segment of the maximum width of a black hole shadow. We can determine the position of a shadow axis through observation of a black hole shadow. For a nonrotating black hole, the minimum interval between the mass center of a black hole and the shadow axis is null. On the other hand, for a rotating black hole the shape and position of the shadow are not symmetric with respect to its rotation axis. So, in this case the minimum interval between the mass center of the black hole and the shadow axis is finite. The extent of this minimum interval is roughly proportional to the spin parameter of a black hole for a fixed inclination angle between a rotation axis and the direction of an observer. The maximum extent of these minimum intervals is about 1.5r<SUB>g</SUB>. Here r<SUB>g</SUB> is a gravitational radius. This is realized in the case of a maximum inclination angle and maximally rotating black hole in an accretion disk in which the inner edge is an event horizon. In order to measure the spin parameter of a black hole, if the shadow axis is determined observationally, it is crucially important to determine the position of the mass center in a region of the shadow. We also discuss how to determine a mass center of a black hole by observation of the shadow on an accretion disk.

[]

https://arxiv.org/pdf/astro-ph/0405099.pdf

2006PhRvD..74f3006D

Short GRB and binary black hole standard sirens as a probe of dark energy

2006-01-01

['-', '-', '-', '-', 'waves', '-', 'gamma rays', 'gamma rays', 'cosmology miscellaneous', 'astrophysics', '-']

[]

Observations of the gravitational radiation from well-localized, inspiraling compact-object binaries can measure absolute source distances with high accuracy. When coupled with an independent determination of redshift through an electromagnetic counterpart, these standard sirens can provide an excellent probe of the expansion history of the Universe and the dark energy. Short γ-ray bursts, if produced by merging neutron star binaries, would be standard sirens with known redshifts detectable by ground-based gravitational wave (GW) networks such as Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), Virgo, and Australian International Gravitational Observatory (AIGO). Depending upon the collimation of these GRBs, the measurement of about 10 GW-GRB events (corresponding to about 1 yr of observation with an advanced GW detector network and an all-sky GRB monitor) can measure the Hubble constant h to ∼2 3%. When combined with measurement of the absolute distance to the last scattering surface of the cosmic microwave background, this determines the dark energy equation of state parameter w to ∼9%. Similarly, supermassive binary black hole inspirals will be standard sirens detectable by Laser Interferometer Space Antenna (LISA). Depending upon the precise redshift distribution, ∼100 sources could measure w at the ∼4% level.

[]

https://arxiv.org/pdf/astro-ph/0601275.pdf

2021ApJ...910..152Z

One Channel to Rule Them All? Constraining the Origins of Binary Black Holes Using Multiple Formation Pathways

2021-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

The second LIGO-Virgo catalog of gravitational-wave (GW) transients has more than quadrupled the observational sample of binary black holes. We analyze this catalog using a suite of five state-of-the-art binary black hole population models covering a range of isolated and dynamical formation channels and infer branching fractions between channels as well as constraints on uncertain physical processes that impact the observational properties of mergers. Given our set of formation models, we find significant differences between the branching fractions of the underlying and detectable populations, and the diversity of detections suggests that multiple formation channels are at play. A mixture of channels is strongly preferred over any single channel dominating the detected population: an individual channel does not contribute to more than ≃70% of the observational sample of binary black holes. We calculate the preference between the natal spin assumptions and common-envelope efficiencies in our models, favoring natal spins of isolated black holes of ≲0.1 and marginally preferring common-envelope efficiencies of ≳2.0 while strongly disfavoring highly inefficient common envelopes. We show that it is essential to consider multiple channels when interpreting GW catalogs, as inference on branching fractions and physical prescriptions becomes biased when contributing formation scenarios are not considered or incorrect physical prescriptions are assumed. Although our quantitative results can be affected by uncertain assumptions in model predictions, our methodology is capable of including models with updated theoretical considerations and additional formation channels.

[]

https://arxiv.org/pdf/2011.10057.pdf

1995PhRvD..51..609S

Conical singularity and quantum corrections to the entropy of a black hole

1995-01-01

['-', '-', '-', '-', '-', '-', '-', '-']

[]

For a general finite temperature different from the Hawking one there appears a well known conical singularity in the Euclidean classical solution of gravitational equations. The method of regularizing the cone by a regular surface is used to determine the curvature tensors for such a metric. This allows one to calculate the one-loop matter effective action and the corresponding one-loop quantum corrections to the entropy in the framework of the path integral approach of Gibbons and Hawking. The two-dimensional (2D) and four-dimensional cases are considered. The entropy of Rindler space is shown to be divergent logarithmically in two dimensions and quadratically in four dimensions that coincides with results obtained earlier. For the eternal 2D black hole we observe a finite, dependent on the mass, correction to the entropy. The entropy of the 4D Schwarzschild black hole is shown to possess an additional (in comparison with the 4D Rindler space) logarithmically divergent correction which does not vanish in the limit of infinite mass of the black hole. We argue that infinities of the entropy in four dimensions are renormalized by the renormalization of the gravitational coupling.

[]

https://arxiv.org/pdf/hep-th/9407001.pdf

2010MNRAS.408..752P

Simulations of magnetized discs around black holes: effects of black hole spin, disc thickness and magnetic field geometry

2010-01-01

['accretion', 'accretion disks', 'black hole physics', 'gravitation', 'hydrodynamics', 'mhd', 'methods numerical', '-', '-']

[]

The standard general relativistic model of a razor-thin accretion disc around a black hole, developed by Novikov &amp; Thorne (NT) in 1973, assumes the shear stress vanishes at the radius of the innermost stable circular orbit (ISCO) and that, outside the ISCO, the shear stress is produced by an effective turbulent viscosity. However, astrophysical accretion discs are not razor thin; it is uncertain whether the shear stress necessarily vanishes at the ISCO, and the magnetic field, which is thought to drive turbulence in discs, may contain large-scale structures that do not behave like a simple local scalar viscosity. We describe 3D general relativistic magnetohydrodynamic simulations of accretion discs around black holes with a range of spin parameters, and we use the simulations to assess the validity of the NT model. Our fiducial initial magnetic field consists of multiple (alternating polarity) poloidal field loops whose shape is roughly isotropic in the disc in order to match the isotropic turbulence expected in the poloidal plane. For a thin disc with an aspect ratio |h/r| ~ 0.07 around a non-spinning black hole, we find a decrease in the accreted specific angular momentum of 2.9 per cent relative to the NT model and an excess luminosity from inside the ISCO of 3.5 per cent. The deviations in the case of spinning black holes are also of the same order. In addition, the deviations decrease with decreasing |h/r|. We therefore conclude that magnetized thin accretion discs in X-ray binaries in the thermal/high-soft spectral state ought to be well described by the NT model, especially at luminosities below 30 per cent of Eddington where we expect a very small disc thickness |h/r| &lt;~ 0.05. We use our results to determine the spin equilibrium of black hole accretion discs with a range of thicknesses and to determine how electromagnetic stresses within the ISCO depend upon black hole spin and disc thickness. We find that the electromagnetic stress and the luminosity inside the ISCO depend on the assumed initial magnetic field geometry. We consider a second geometry with field lines following density contours, which for thin discs leads to highly radially elongated magnetic field lines. This gives roughly twice larger deviations from NT for both the accreted specific angular momentum and the luminosity inside the ISCO. Lastly, we find that the disc's corona (including any wind or jet) introduces deviations from NT in the specific angular momentum that are comparable to those contributed by the disc component, while the excess luminosity of bound gas from within the ISCO is dominated by only the disc component. Based on these indications, we suggest that differences in results between our work and other similar work are due to differences in the assumed initial magnetic field geometry as well as the inclusion of disc gas versus all the gas when comparing the specific angular momentum from the simulations with the NT model.

[]

https://arxiv.org/pdf/1003.0966.pdf

2015CQGra..32m4001B

Black holes as particle detectors: evolution of superradiant instabilities

2015-01-01

['black hole physics', '-', 'gravitational waves', 'accretion', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

Superradiant instabilities of spinning black holes (BHs) can be used to impose strong constraints on ultralight bosons, thus turning BHs into effective particle detectors. However, very little is known about the development of the instability and whether its nonlinear time evolution accords to the linear intuition. For the first time, we attack this problem by studying the impact of gravitational-wave (GW) emission and gas accretion on the evolution of the instability. Our quasi-adiabatic, fully-relativistic analysis shows that: (i) GW emission does not have a significant effect on the evolution of the BH, (ii) accretion plays an important role, and (iii) although the mass of the scalar cloud developed through superradiance can be a sizeable fraction of the BH mass, its energy-density is very low and backreaction is negligible. Thus, massive BHs are well described by the Kerr geometry even if they develop bosonic clouds through superradiance. Using Monte Carlo methods and very conservative assumptions, we provide strong support to the validity of the linearized analysis and to the bounds of previous studies.

[]

https://arxiv.org/pdf/1411.0686.pdf

2012PhRvD..85f4019A

Shadow of a rotating braneworld black hole

2012-01-01

['-', '-', '-', '-', '-', 'theory', '-', '-']

[]

We investigate the shadow cast by a rotating braneworld black hole, in the Randall-Sundrum scenario. In addition to the angular momentum, the tidal charge term deforms the shape of the shadow. For a given value of the rotation parameter, the presence of a negative tidal charge enlarges the shadow and reduces its deformation with respect to Kerr spacetime, while for a positive charge, the opposite effect is obtained. We also analyze the case in which the combination of the rotation parameter and the tidal charge results in a naked singularity. We discuss the observational prospects corresponding to the supermassive black hole at the Galactic center.

[]

https://arxiv.org/pdf/1112.6349.pdf

2004ApJ...611..623S

Low-Frequency Gravitational Radiation from Coalescing Massive Black Hole Binaries in Hierarchical Cosmologies

2004-01-01

['black hole physics', 'cosmology theory', 'cosmology early universe', 'gravitational waves', 'relativity', 'astrophysics']

[]

We compute the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at the center of galaxies in a hierarchical structure formation scenario in which seed holes of intermediate mass form far up in the dark halo ``merger tree.'' The merger history of dark matter halos and associated MBHs is followed via cosmological Monte Carlo realizations of the merger hierarchy from redshift z=20 to the present in a ΛCDM cosmology. MBHs get incorporated through halo mergers into larger and larger structures, sink to the center because of dynamical friction against the dark matter background, accrete cold material in the merger remnant, and form MBH binary systems. Stellar dynamical (three-body) interactions cause the hardening of the binary at large separations, while gravitational wave emission takes over at small radii and leads to the final coalescence of the pair. A simple scheme is applied in which the ``loss cone'' is constantly refilled and a constant stellar density core forms because of the ejection of stars by the shrinking binary. The integrated emission from inspiraling MBH binaries at all redshifts is computed in the quadrupole approximation and results in a gravitational wave background (GWB) with a well-defined shape that reflects the different mechanisms driving the late orbital evolution. The characteristic strain spectrum has the standard h<SUB>c</SUB>(f)~f<SUP>-2/3</SUP> behavior only in the range f=10<SUP>-9</SUP>to10<SUP>-6</SUP> Hz. At lower frequencies the orbital decay of MBH binaries is driven by the ejection of background stars (``gravitational slingshot''), and the strain amplitude increases with frequency, h<SUB>c</SUB>(f)~f. In this range the GWB is dominated by 10<SUP>9</SUP>-10<SUP>10</SUP> M<SUB>solar</SUB> MBH pairs coalescing at 0&lt;~z&lt;~2. At higher frequencies, f&gt;10<SUP>-6</SUP>Hz, the strain amplitude, as steep as h<SUB>c</SUB>(f)~f<SUP>-1.3</SUP>, is shaped by the convolution of last stable circular orbit emission by lighter binaries (10<SUP>2</SUP>-10<SUP>7</SUP> M<SUB>solar</SUB>) populating galaxy halos at all redshifts. We discuss the observability of inspiraling MBH binaries by a low-frequency gravitational wave experiment such as the planned Laser Interferometer Space Antenna (LISA). Over a 3 yr observing period LISA should resolve this GWB into discrete sources, detecting ~60 (~250) individual events above an S/N=5 (S/N=1) confidence level.

[]

https://arxiv.org/pdf/astro-ph/0401543.pdf

2008ApJ...679..118S

The Luminosity Function of X-Ray-selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift

2008-01-01

['galaxies active', 'galaxies quasars', 'surveys', 'astronomy x rays', 'astrophysics']

[]

We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of AGNs up to z ~ 5. At high redshifts, the wide area coverage of the Chandra Multiwavength Project is crucial to detect rare and luminous (L<SUB>X</SUB> &gt; 10<SUP>44</SUP> ergs s<SUP>-1</SUP>) AGNs. The inclusion of samples from deeper published surveys, such as the Chandra Deep Fields, allows us to span the lower L<SUB>X</SUB> range of the XLF. Our sample is selected from both the hard (z &lt; 3, f<SUB>2-8 keV</SUB> &gt; 6.3 × 10<SUP>-16</SUP> ergs cm <SUP>-2</SUP> s<SUP>-1</SUP>) and soft (z &gt; 3, f<SUB>0.5-2.0 keV</SUB> &gt; 1.0 × 10<SUP>-16</SUP> ergs cm <SUP>-2</SUP> s<SUP>-1</SUP>) energy band detections. Within our optical magnitude limits (r', i' &lt; 24), we achieve an adequate level of completeness (&gt;50%) regarding X-ray source identification (i.e., redshift). We find that the luminosity function is similar to that found in previous X-ray surveys up to z ~ 3 with an evolution dependent on both luminosity and redshift. At z &gt; 3, there is a significant decline in the numbers of AGNs with an evolution rate similar to that found by studies of optically selected QSOs. Based on our XLF, we assess the resolved fraction of the cosmic X-ray background, the cumulative mass density of SMBHs, and the comparison of the mean accretion rate onto SMBHs and the star formation history of galaxies as a function of redshift. A coevolution scenario up to z ~ 2 is plausible, although at higher redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we highlight the need for better statistics of high-redshift AGNs at z gtrsim 3, which is achievable with the upcoming Chandra surveys.

[]

https://arxiv.org/pdf/0710.2461.pdf

1994PhRvD..49.2909D

Pair creation of dilaton black holes

1994-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

We consider dilaton gravity theories in four spacetime dimensions parametrized by a constant a, which controls the dilaton coupling, and construct new exact solutions. We first generalize the C metric of Einstein-Maxwell theory (a=0) to solutions corresponding to oppositely charged dilaton black holes undergoing uniform acceleration for general a. We next develop a solution-generating technique which allows us to ``embed'' the dilaton C metrics in magnetic dilaton Melvin backgrounds, thus generalizing the Ernst metric of Einstein-Maxwell theory. By adjusting the parameters appropriately, it is possible to eliminate the nodal singularities of the dilaton C metrics. For a&lt;1 (but not for a&gt;=1), it is possible to further restrict the parameters so that the dilaton Ernst solutions have a smooth Euclidean section with topology S<SUP>2</SUP>×S<SUP>2</SUP>-\{pt\}, corresponding to instantons describing the pair production of dilaton black holes in a magnetic field. A different restriction on the parameters leads to smooth instantons for all values of a with topology S<SUP>2</SUP>×openR<SUP>2</SUP>.

[]

https://arxiv.org/pdf/hep-th/9309075.pdf

2000PhRvD..62h4013C

Black hole scan

2000-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

Gravitation theories selected by requiring that they have a unique anti-de Sitter vacuum with a fixed cosmological constant are studied. For a given dimension d, the Lagrangians under consideration are labeled by an integer k=1,2,...,[(d-1)/2]. Black holes for each d and k are found and are used to rank these theories. A minimum possible size for a localized electrically charged source is predicted in the whole set of theories, except general relativity. It is found that the thermodynamic behavior falls into two classes: If d-2k=1, these solutions resemble the three dimensional black hole; otherwise, their behavior is similar to the Schwarzschild-AdS<SUB>4</SUB> geometry.

[]

https://arxiv.org/pdf/hep-th/0003271.pdf

1998ApJ...505..854E

Spectral Transitions in Cygnus X-1 and Other Black Hole X-Ray Binaries

1998-01-01

['accretion', 'accretion disks', 'black hole physics', '-', '-', '-', 'astronomy x rays', 'accretion', 'accretion disks', 'black hole physics', '-', '-', '-', 'astronomy x rays', 'astrophysics']

[]

We show that the model proposed by Esin, McClintock, &amp; Narayan for the low state, intermediate state, and high state of the black hole soft X-ray transient, Nova Muscae 1991, is consistent with the spectral evolution of the black hole X-ray binary, Cyg X-1, during the hard-to-soft state transition observed in 1996. We also apply the model to the outbursts of two other black hole X-ray transients, GRO J0422+32 and GRO J1719-24.

[]

https://arxiv.org/pdf/astro-ph/9711167.pdf

2004ApJ...601L.159G

Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way

2004-01-01

['black hole physics', 'galaxy center', 'astronomy infrared', 'techniques high angular resolution', 'astrophysics']

[]

We report the detection of a variable point source, imaged at L<SUP>'</SUP> (3.8 μm) with the Keck II 10 m telescope's adaptive optics system, that is coincident to within 18 mas (1 σ) of the Galaxy's central supermassive black hole and the unique radio source Sgr A*. While in 2002 this source (Sgr A* IR) was confused with the stellar source S0-2, in 2003 these two sources are separated by 87 mas, allowing the new source's properties to be determined directly. On four separate nights, its observed L<SUP>'</SUP> magnitude ranges from 12.2 to 13.8, which corresponds to a dereddened flux density of 4-17 mJy; no other source in this region shows such large variations in flux density-a factor of 4 over a week and a factor of 2 over 40 minutes. In addition, it has a K-L<SUP>'</SUP> color greater than 2.1, which is at least 1 mag redder than any other source detected at L<SUP>'</SUP> in its vicinity. Based on this source's coincidence with the Galaxy's dynamical center, its lack of motion, its variability, and its red color, we conclude that it is associated with the central supermassive black hole. The short timescale for the 3.8 μm flux density variations implies that the emission arises quite close to the black hole, within 5 AU, or 80R<SUB>s</SUB>. We suggest that both the variable 3.8 μm emission and the X-ray flares arise from the same underlying physical process, possibly the acceleration of a small population of electrons to ultrarelativistic energies. In contrast to the X-ray flares, which are only detectable ~2% of the time, the 3.8 μm emission provides a new, constantly accessible window into the physical conditions of the plasma in close proximity to the central black hole.

[]

https://arxiv.org/pdf/astro-ph/0309076.pdf

2007ApJ...667..131G

The Mass Function of Active Black Holes in the Local Universe

2007-01-01

['galaxies active', 'galaxies nuclei', 'galaxies seyfert', 'astrophysics']

[]

We present the first measurement of the BH mass function for broad-line active galaxies in the local universe. Using the ~8500 broad-line active galaxies from SDSS DR4, we construct a broad-line luminosity function that agrees very well with the local soft X-ray luminosity function. Using standard virial relations, we then convert observed broad-line luminosities and widths into BH masses. A mass function constructed in this way has the unique capability to probe the mass region &lt;10<SUP>6</SUP> M<SUB>solar</SUB>, which, while insignificant in terms of total BH mass density, nevertheless may place important constraints on the mass distribution of seed BHs in the early universe. The characteristic local active BH has a mass of ~10<SUP>7</SUP> M<SUB>solar</SUB> radiating at 10% of the Eddington rate. The active fraction is a strong function of BH mass; at both higher and lower masses the active mass function falls more steeply than one would infer from the distribution of bulge luminosity. The deficit of local massive radiating BHs is a well-known phenomenon, while we present the first robust measurement of a decline in the space density of active BHs at low mass.

[]

https://arxiv.org/pdf/0705.0020.pdf

2005PhRvD..71b4035B

Three-dimensional relativistic simulations of rotating neutron-star collapse to a Kerr black hole

2005-01-01

['-', '-', '-', '-', 'methods numerical', 'relativity', '-', 'neutron', '-', 'astrophysics']

[]

We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations. Besides presenting a thorough set of tests which the code passes with very high accuracy, we discuss its application to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. The initial stellar models are modeled as relativistic polytropes which are either secularly or dynamically unstable and with angular velocities which range from slow rotation to the mass-shedding limit. We investigate the gravitational collapse by carefully studying not only the dynamics of the matter, but also that of the trapped surfaces, i.e., of both the apparent and event horizons formed during the collapse. The use of these surfaces, together with the dynamical horizon framework, allows for a precise measurement of the black-hole mass and spin. The ability to successfully perform these simulations for sufficiently long times relies on excising a region of the computational domain which includes the singularity and is within the apparent horizon. The dynamics of the collapsing matter is strongly influenced by the initial amount of angular momentum in the progenitor star and, for initial models with sufficiently high angular velocities, the collapse can lead to the formation of an unstable disc in differential rotation. All of the simulations performed with uniformly rotating initial data and a polytropic or ideal-fluid equation of state show no evidence of shocks or of the presence of matter on stable orbits outside the black hole.

[]

https://arxiv.org/pdf/gr-qc/0403029.pdf

2002ApJ...573..738H

The Dynamical Structure of Nonradiative Black Hole Accretion Flows

2002-01-01

['accretion', 'accretion disks', 'black hole physics', 'instabilities', 'mhd', 'astrophysics']

[]

We analyze three-dimensional magnetohydrodynamic simulations of a nonradiative accretion flow around a black hole using a pseudo-Newtonian potential. The flow originates from a torus initially centered at 100 gravitational (Schwarzschild) radii. Accretion is driven by turbulent stresses generated self-consistently by the magnetorotational instability. The resulting flow has three well-defined dynamical components: a hot, thick, rotationally dominated Keplerian disk; a surrounding magnetized corona with vigorous circulation and outflow; and a magnetically confined jet along the centrifugal funnel wall. Inside 10 gravitational radii, the disk becomes very hot, more toroidal, and highly intermittent. These results contrast sharply with quasi-spherical, self-similar viscous models. There are no significant dynamical differences between simulations that include resistive heating and those that do not. We conclude by deducing some simple radiative properties of our solutions, and apply the results to the accretion-powered Galactic center source Sgr A*.

[]

https://arxiv.org/pdf/astro-ph/0203309.pdf

2009ApJ...700.1952H

The Population of Viscosity- and Gravitational Wave-driven Supermassive Black Hole Binaries Among Luminous Active Galactic Nuclei

2009-01-01

['black hole physics', 'galaxies nuclei', 'gravitational waves', '-']

[]

Supermassive black hole binaries (SMBHBs) in galactic nuclei are thought to be a common by-product of major galaxy mergers. We use simple disk models for the circumbinary gas and for the binary-disk interaction to follow the orbital decay of SMBHBs with a range of total masses (M) and mass ratios (q), through physically distinct regions of the disk, until gravitational waves (GWs) take over their evolution. Prior to the GW-driven phase, the viscous decay is generically in the stalled "secondary-dominated" regime. SMBHBs spend a non-negligible fraction of a fiducial time of 10<SUP>7</SUP> yr at orbital periods between days lsimt <SUB>orb</SUB>lsim yr, and we argue that they may be sufficiently common to be detectable, provided they are luminous during these stages. A dedicated optical or X-ray survey could identify coalescing SMBHBs statistically, as a population of periodically variable quasars, whose abundance obeys the scaling N <SUB>var</SUB> vprop t <SUP>α</SUP> <SUB>var</SUB> within a range of periods around t <SUB>var</SUB>~ tens of weeks. SMBHBs with M lsim 10<SUP>7</SUP> M <SUB>sun</SUB>, with 0.5 lsim α lsim 1.5, would probe the physics of viscous orbital decay, whereas the detection of a population of higher-mass binaries, with α = 8/3, would confirm that their decay is driven by GWs. The lowest-mass SMBHBs (M lsim 10<SUP>5-6</SUP> M <SUB>sun</SUB>) enter the GW-driven regime at short orbital periods, when they are already in the frequency band of the Laser Interferometric Space Antenna (LISA). While viscous processes are negligible in the last few years of coalescence, they could reduce the amplitude of any unresolved background due to near-stationary LISA sources. We discuss modest constraints on the SMBHB population already available from existing data, and the sensitivity and sky coverage requirements for a detection in future surveys. SMBHBs may also be identified from velocity shifts in their spectra; we discuss the expected abundance of SMBHBs as a function of their orbital velocity.

[]

https://arxiv.org/pdf/0904.1383.pdf

2001PhRvD..64d4006H

Hawking radiation from AdS black holes

2001-01-01

['-', '-', '-', '-', '-']

[]

We investigate Hawking radiation from black holes in (d+1)-dimensional anti-de Sitter space. We focus on s waves, make use of the geometrical optics approximation, and follow three approaches to analyze the radiation. First, we compute a Bogoliubov transformation between Kruskal and asymptotic coordinates and compare the different vacua. Second, following a method due to Kraus, Parikh, and Wilczek, we view Hawking radiation as a tunneling process across the horizon and compute the tunneling probability. This approach uses an anti-de Sitter version of a metric originally introduced by Painlevé for Schwarzschild black holes. From the tunneling probability one also finds a leading correction to the semiclassical emission rate arising from back reaction to the background geometry. Finally, we consider a spherically symmetric collapse geometry and the Bogoliubov transformation between the initial vacuum state and the vacuum of an asymptotic observer.

[]

https://arxiv.org/pdf/gr-qc/0005115.pdf

1999A&A...350..148W

Implications of massive close binaries for black hole formation and supernovae

1999-01-01

['stars circumstellar matter', '-', '-', '-', 'stars white dwarfs', 'astrophysics']

[]

The progenitor evolution of the massive X-ray binary Wray 977 is investigated using new models of massive close binary evolution. These models yield constraints on the mass limit for neutron star/black hole formation in single stars, M_BH. We argue for quasi-conservative evolution in this system, and we find M_BH &gt; 13..21 M_sun from the existence of a neutron star in Wray 977, with the uncertainty being due to uncertainties in the treatment of convection. Our results revise earlier published much larger values of M_BH derived from the parameters of Wray 977. Then, on the basis of a grid of 37 evolutionary models for massive close binaries with various initial masses, mass ratios and periods, we derive primary initial-final mass, initial mass-final helium core mass, and initial mass-final CO-core mass relations for the various mass transfer cases of close binary evolution. From these models we derive for single stars that M_BH ~&lt; 25 M_sun, independent of whether most black hole binaries formed through the Case A/B or the Case C binary channel. Using our grid of binary models, we obtain a consistent scenario for the formation of black holes in binary systems. We emphasize that in binaries the critical initial mass limits for neutron star/black hole formation and for white dwarf/neutron star formation are very different from the corresponding values in single stars. While the first may well be above 100 M_sun in Case A/B binaries, the latter is found to be in the range 12...15 M_sun instead of the canonical value of 8...10 M_sun usually quoted for single stars. This effect should not be neglected in population synthesis studies of massive binary systems. Also, neutron star and black hole mass functions obtained for single stars can not per se compared to the masses of compact objects in binary systems. Massive close binaries produce also Type Ib and Ic supernovae. We find two different types of supernova progenitor structure in our models, one with remaining helium masses of the order of 1 M_sun which stems from an intermediate progenitor initial mass range (about 16...25 M_sun), and another with one order of magnitude smaller remaining helium masses from initial masses above and below this. A possible connection to the distinction of Type Ib and Type Ic supernovae, and implications from the Type Ic supernova SN1998bw and its associated gamma-ray burst are discussed.

[]

https://arxiv.org/pdf/astro-ph/9904256.pdf

2005PhRvL..94x1301D

Exact Counting of Supersymmetric Black Hole Microstates

2005-01-01

['-', '-', '-', '-', '-']

[]

It is shown that the entropy of certain two-charge supersymmetric black holes in N=4 string theories can be computed to all orders using Wald’s formula and the supersymmetric attractor equations with an effective action that includes the relevant higher curvature terms. Classically, these black holes have zero area but the attractor equations are still applicable at the quantum level and result in finite quantum area. The quantum corrected macroscopic entropy agrees precisely with the microscopic counting for an infinite tower of fundamental string states to all orders in an asymptotic expansion.

[]

https://arxiv.org/pdf/hep-th/0409148.pdf

2003PhRvL..90p1301K

d-Dimensional Black Hole Entropy Spectrum from Quasinormal Modes

2003-01-01

['-', '-', '-', '-', '-', 'black hole physics', '-', '-']

[]

Starting from recent observations about quasinormal modes, we use semiclassical arguments to derive the Bekenstein-Hawking entropy spectrum for d-dimensional spherically symmetric black holes. We find that, as first suggested by Bekenstein, the entropy spectrum is equally spaced: S<SUB>BH</SUB>=kln((m<SUB>0</SUB>)n, where m<SUB>0</SUB> is a fixed integer that must be derived from the microscopic theory. As shown in O. Dreyer, gr-qc/0211076, 4D loop quantum gravity yields precisely such a spectrum with m<SUB>0</SUB>=3 providing the Immirzi parameter is chosen appropriately. For d-dimensional black holes of radius R<SUB>H</SUB>(M), our analysis predicts the existence of a unique quasinormal mode frequency in the large damping limit ω<SUP>(d)</SUP>(M)=α<SUP>(d)</SUP>c/R<SUB>H</SUB>(M) with coefficient α<SUP>(d)</SUP>=(d-3)/4πln((m<SUB>0</SUB>), where m<SUB>0</SUB> is an integer.

[]

https://arxiv.org/pdf/gr-qc/0212014.pdf

2019PhRvD.100d3027R

Black holes: The next generation—repeated mergers in dense star clusters and their gravitational-wave properties

2019-01-01

['-', '-']

[]

When two black holes merge in a dense star cluster, they form a new black hole with a well-defined mass and spin. If that "second-generation" black hole remains in the cluster, it will continue to participate in dynamical encounters, form binaries, and potentially merge again. Using a grid of 96 dynamical models of dense star clusters and a cosmological model of cluster formation, we explore the production of binary black hole mergers where at least one component of the binary was forged in a previous merger. We create four hypothetical universes where every black hole born in the collapse of a massive star has a dimensionless Kerr spin parameter, χ<SUB>birth</SUB> , of 0.0, 0.1, 0.2, or 0.5. We show that if all stellar-born black holes are nonspinning (χ<SUB>birth</SUB>=0.0 ), then more than 10% of merging binary black holes from clusters have components formed from previous mergers, accounting for more than 20% of the mergers from globular clusters detectable by LIGO/Virgo. Furthermore, nearly 7% of detectable mergers would have a component with a mass ≳55 M<SUB>⊙</SUB>, placing it clearly in the mass "gap" region where black holes cannot form from isolated collapsing stars due to the pulsational-pair instability mechanism. On the other hand, if black holes are born spinning, then the contribution from these second-generation mergers decreases, making up as little as 1% of all detections from globular clusters when χ<SUB>birth</SUB>=0.5 . We make quantitative predictions for the detected masses, mass ratios, and spin properties of first- and second-generation mergers from dense star clusters, and show how these distributions are highly sensitive to the birth spins of black holes.

[]

https://arxiv.org/pdf/1906.10260.pdf

2005ApJ...622L..93M

The Afterglow of Massive Black Hole Coalescence

2005-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxies quasars', 'astronomy x rays', 'astrophysics', '-']

[]

The final merger of a pair of massive black holes in a galactic nucleus is compelled by gravitational radiation. Gravitational waves from the mergers of black holes of masses 10<SUP>5</SUP>-10<SUP>7</SUP>(1+z)<SUP>-1</SUP> M<SUB>solar</SUB> at redshifts of 1-20 will be readily detectable by the Laser Interferometer Space Antenna, but an electromagnetic afterglow would be helpful in pinpointing the source and its redshift. Long before the merger, the binary ``hollows out'' any surrounding gas and shrinks slowly compared to the viscous timescale of a circumbinary disk. The inner gas disk is truncated at the radius where gravitational torque from the binary balances the viscous torque, and accretion onto the black holes is diminished. Initially, the inner truncation radius is able to follow the shrinking binary inward. But eventually the gravitational radiation timescale becomes shorter than the viscous timescale in the disk, leading to a merged black hole surrounded by a hollow disk of gas. We show that the subsequent viscous evolution of the hollow, radiation pressure-dominated disk will create an ~10<SUP>43.5</SUP>(M/10<SUP>6</SUP> M<SUB>solar</SUB>) ergs s<SUP>-1</SUP> X-ray source on a timescale ~7(1+z)(M/10<SUP>6</SUP> M<SUB>solar</SUB>)<SUP>1.32</SUP> yr. This justifies follow-up monitoring of gravitational wave events with next-generation X-ray observatories. Analysis of the detailed light curve of these afterglows will yield new insights into the subtle physics of accretion onto massive black holes.

[]

https://arxiv.org/pdf/astro-ph/0410343.pdf

2018PhLB..776..345E

Primordial black hole production in Critical Higgs Inflation

2018-01-01

['-', '-', '-', '-']

[]

Primordial Black Holes (PBH) arise naturally from high peaks in the curvature power spectrum of near-inflection-point single-field inflation, and could constitute today the dominant component of the dark matter in the universe. In this letter we explore the possibility that a broad spectrum of PBH is formed in models of Critical Higgs Inflation (CHI), where the near-inflection point is related to the critical value of the RGE running of both the Higgs self-coupling λ (μ) and its non-minimal coupling to gravity ξ (μ). We show that, for a wide range of model parameters, a half-domed-shaped peak in the matter spectrum arises at sufficiently small scales that it passes all the constraints from large scale structure observations. The predicted cosmic microwave background spectrum at large scales is in agreement with Planck 2015 data, and has a relatively large tensor-to-scalar ratio that may soon be detected by B-mode polarization experiments. Moreover, the wide peak in the power spectrum gives an approximately lognormal PBH distribution in the range of masses 0.01- 100M<SUB>⊙</SUB>, which could explain the LIGO merger events, while passing all present PBH observational constraints. The stochastic background of gravitational waves coming from the unresolved black-hole-binary mergers could also be detected by LISA or PTA. Furthermore, the parameters of the CHI model are consistent, within 2σ, with the measured Higgs parameters at the LHC and their running. Future measurements of the PBH mass spectrum could allow us to obtain complementary information about the Higgs couplings at energies well above the EW scale, and thus constrain new physics beyond the Standard Model.

[]

https://arxiv.org/pdf/1705.04861.pdf

2015MNRAS.454.1038R

The impact of angular momentum on black hole accretion rates in simulations of galaxy formation

2015-01-01

['black hole physics', 'methods numerical', 'galaxies active', 'galaxies evolution', 'galaxies formation', 'galaxies quasars', '-']

[]

Feedback from energy liberated by gas accretion on to black holes (BHs) is an attractive mechanism to explain the exponential cut-off at the massive end of the galaxy stellar mass function. Most previous implementations of BH accretion in hydrodynamical simulations of galaxy formation have assumed that BHs grow at an accretion rate that is proportion to the Bondi rate. A major concern is that the Bondi accretion rate is inappropriate when the accreting material has significant angular momentum. We present an improved accretion model that takes into account the circularization and subsequent viscous transport of infalling material, and implemented as a `subgrid' model in hydrodynamic simulations. The resulting accretion rates are generally low in low mass (≲ 10<SUP>11.5</SUP> M<SUB>⊙</SUB>) haloes, but show outbursts of Eddington-limited accretion during galaxy mergers. During outbursts these objects strongly resemble quasars. In higher mass haloes, gas accretion peaks at ∼10 per cent of the Eddington rate, which is thought to be conducive to the formation of radio jets. The resulting accretion rate depends strongly on the effective pressure of the gas surrounding the BH, which in turn depends strongly on halo mass. This induces a sharp transition in the importance of BH feedback. In small haloes, the growth of galaxies is regulated by star formation and supernova feedback, but above a halo mass of 10<SUP>11.5</SUP> M<SUB>⊙</SUB>, rapid BH growth leads to the suppression of star formation and reduced growth of stellar mass with increasing halo mass.

[]

https://arxiv.org/pdf/1312.0598.pdf

2017JCAP...09..013G

Gravitational wave signatures of inflationary models from Primordial Black Hole dark matter

2017-01-01

['-', '-', '-']

[]

Primordial Black Holes (PBH) could be the cold dark matter of the universe. They could have arisen from large (order one) curvature fluctuations produced during inflation that reentered the horizon in the radiation era. At reentry, these fluctuations source gravitational waves (GW) via second order anisotropic stresses. These GW, together with those (possibly) sourced during inflation by the same mechanism responsible for the large curvature fluctuations, constitute a primordial stochastic GW background (SGWB) that unavoidably accompanies the PBH formation. We study how the amplitude and the range of frequencies of this signal depend on the statistics (Gaussian versus χ<SUP>2</SUP>) of the primordial curvature fluctuations, and on the evolution of the PBH mass function due to accretion and merging. We then compare this signal with the sensitivity of present and future detectors, at PTA and LISA scales. We find that this SGWB will help to probe, or strongly constrain, the early universe mechanism of PBH production. The comparison between the peak mass of the PBH distribution and the peak frequency of this SGWB will provide important information on the merging and accretion evolution of the PBH mass distribution from their formation to the present era. Different assumptions on the statistics and on the PBH evolution also result in different amounts of CMB μ-distortions. Therefore the above results can be complemented by the detection (or the absence) of μ-distortions with an experiment such as PIXIE.

[]

https://arxiv.org/pdf/1707.02441.pdf

2017MNRAS.465...32B

The dark nemesis of galaxy formation: why hot haloes trigger black hole growth and bring star formation to an end

2017-01-01

['black hole physics', 'galaxies active', 'galaxies formation', 'galaxies quasars', '-']

[]

Galaxies fall into two clearly distinct types: `blue-sequence' galaxies which are rapidly forming young stars, and `red-sequence' galaxies in which star formation has almost completely ceased. Most galaxies more massive than 3 × 10<SUP>10</SUP> M<SUB>⊙</SUB> follow the red sequence, while less massive central galaxies lie on the blue sequence. We show that these sequences are created by a competition between star formation-driven outflows and gas accretion on to the supermassive black hole at the galaxy's centre. We develop a simple analytic model for this interaction. In galaxies less massive than 3 × 10<SUP>10</SUP> M<SUB>⊙</SUB>, young stars and supernovae drive a high-entropy outflow which is more buoyant than any tenuous corona. The outflow balances the rate of gas inflow, preventing high gas densities building up in the central regions. More massive galaxies, however, are surrounded by an increasingly hot corona. Above a halo mass of ∼10<SUP>12</SUP> M<SUB>⊙</SUB>, the outflow ceases to be buoyant and star formation is unable to prevent the build-up of gas in the central regions. This triggers a strongly non-linear response from the black hole. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for star formation. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. We show that the analytic model provides a good description of galaxy evolution in the EAGLE hydrodynamic simulations. So long as star formation-driven outflows are present, the transition mass scale is almost independent of subgrid parameter choice.

[]

https://arxiv.org/pdf/1607.07445.pdf

1993bhmw.conf...22P

Do Black Holes Destroy Information?

1993-01-01

['-', '-']

[]

I review the information loss paradox that was first formulated by Hawking, and discuss possible ways of resolving it. All proposed solutions have serious drawbacks. I conclude that the information loss paradox may well presage a revolution in fundamental physics. (To appear in the proceedings of the International Symposium on Black Holes, Membranes, Wormholes, and Superstrings.)

[]

https://arxiv.org/pdf/hep-th/9209058.pdf

2018ApJ...856..140H

Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai-Lidov Effect

2018-01-01

['black hole physics', '-', 'gravitational waves', 'stars kinematics and dynamics', '-']

[]

Nuclear star clusters around a central massive black hole (MBH) are expected to be abundant in stellar black hole (BH) remnants and BH-BH binaries. These binaries form a hierarchical triple system with the central MBH, and gravitational perturbations from the MBH can cause high-eccentricity excitation in the BH-BH binary orbit. During this process, the eccentricity may approach unity, and the pericenter distance may become sufficiently small so that gravitational-wave emission drives the BH-BH binary to merge. In this work, we construct a simple proof-of-concept model for this process, and specifically, we study the eccentric Kozai-Lidov mechanism in unequal-mass, soft BH-BH binaries. Our model is based on a set of Monte Carlo simulations for BH-BH binaries in galactic nuclei, taking into account quadrupole- and octupole-level secular perturbations, general relativistic precession, and gravitational-wave emission. For a typical steady-state number of BH-BH binaries, our model predicts a total merger rate of ∼1-3 {Gpc} <SUP>-3</SUP> {yr} <SUP>-1</SUP>, depending on the assumed density profile in the nucleus. Thus, our mechanism could potentially compete with other dynamical formation processes for merging BH-BH binaries, such as the interactions of stellar BHs in globular clusters or in nuclear star clusters without an MBH.

[]

https://arxiv.org/pdf/1706.09896.pdf

2015MNRAS.453.1562G

A systematic search for close supermassive black hole binaries in the Catalina Real-time Transient Survey

2015-01-01

['methods data analysis', 'techniques photometric', 'surveys', 'galaxies quasars', 'galaxies quasars', '-', '-']

[]

Hierarchical assembly models predict a population of supermassive black hole (SMBH) binaries. These are not resolvable by direct imaging but may be detectable via periodic variability (or nanohertz frequency gravitational waves). Following our detection of a 5.2-year periodic signal in the quasar PG 1302-102, we present a novel analysis of the optical variability of 243 500 known spectroscopically confirmed quasars using data from the Catalina Real-time Transient Survey (CRTS) to look for close (&lt;0.1 pc) SMBH systems. Looking for a strong Keplerian periodic signal with at least 1.5 cycles over a baseline of nine years, we find a sample of 111 candidate objects. This is in conservative agreement with theoretical predictions from models of binary SMBH populations. Simulated data sets, assuming stochastic variability, also produce no equivalent candidates implying a low likelihood of spurious detections. The periodicity seen is likely attributable to either jet precession, warped accretion discs or periodic accretion associated with a close SMBH binary system. We also consider how other SMBH binary candidates in the literature appear in CRTS data and show that none of these are equivalent to the identified objects. Finally, the distribution of objects found is consistent with that expected from a gravitational-wave-driven population. This implies that circumbinary gas is present at small orbital radii and is being perturbed by the black holes. None of the sources is expected to merge within at least the next century. This study opens a new unique window to study a population of close SMBH binaries that must exist according to our current understanding of galaxy and SMBH evolution.

[]

https://arxiv.org/pdf/1507.07603.pdf

2023ApJ...952L..37A

The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background

2023-01-01

['gravitational waves', '-', 'galaxy evolution', '-', '-', '-', '-', '-', '-']

[]

The NANOGrav 15 yr data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15 yr observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach subparsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations.

[]

https://arxiv.org/pdf/2306.16220.pdf

2005CQGra..22R..85C

TOPICAL REVIEW: Conformal field theory, (2 + 1)-dimensional gravity and the BTZ black hole

2005-01-01

['-', '-']

[]

In three spacetime dimensions, general relativity becomes a topological field theory, whose dynamics can be largely described holographically by a two-dimensional conformal field theory at the 'boundary' of spacetime. I review what is known about this reduction—mainly within the context of pure (2 + 1)-dimensional gravity—and discuss its implications for our understanding of the statistical mechanics and quantum mechanics of black holes.

[]

https://arxiv.org/pdf/gr-qc/0503022.pdf

2012ApJ...757...36K

Mass Measurements of Black Holes in X-Ray Transients: Is There a Mass Gap?

2012-01-01

['black hole physics', 'astronomy x rays', '-', '-']

[]

We explore possible systematic errors in the mass measurements of stellar mass black holes (BHs). We find that significant errors can arise from the assumption of zero or constant emission from the accretion flow, which is commonly used when determining orbital inclination by modeling ellipsoidal variations. For A0620-00, the system with the best available data, we show that typical data sets and analysis procedures can lead to systematic underestimates of the inclination by 10° or more. A careful examination of the available data for the 15 other X-ray transients with low-mass donors suggests that this effect may significantly reduce the BH mass estimates in several other cases, most notably that of GRO J0422+32. Assuming that GRO J0422+32 behaves similarly to A0620-00, the reduction in the mass of GRO J0422+32 fills the mass gap between the low end of the distribution and the maximum theoretical neutron star mass, as has been identified in previous studies. Otherwise, we find that the mass distribution retains other previously identified characteristics, namely a peak around 8 M <SUB>⊙</SUB>, a paucity of sources with masses below 5 M <SUB>⊙</SUB>, and a sharp drop-off above 10 M <SUB>⊙</SUB>.

[]

https://arxiv.org/pdf/1205.1805.pdf

2015PhRvD..91b4032C

Thermodynamics of black holes in massive gravity

2015-01-01

['-', '-', '-', '-', '-', '-', '-', '-']

[]

We present a class of charged black hole solutions in an (n +2 )-dimensional massive gravity with a negative cosmological constant, and study the thermodynamics and phase structure of the black hole solutions in both the grand canonical and canonical ensembles. The black hole horizon can have a positive, zero, or negative constant curvature characterized by the constant k . By using the Hamiltonian approach, we obtain conserved charges of the solutions and find that the black hole entropy still obeys the area formula and the gravitational field equation at the black hole horizon can be cast into a form similar to the first law of black hole thermodynamics. In the grand canonical ensemble, we find that the thermodynamics and phase structure depend on the combination k -μ<SUP>2</SUP>/4 +c<SUB>2</SUB>m<SUP>2</SUP> in the four-dimensional case, where μ is the chemical potential and c<SUB>2</SUB>m<SUP>2</SUP> is the coefficient of the second term in the potential associated with the graviton mass. When it is positive, the Hawking-Page phase transition can happen; when as it is negative, the black hole is always thermodynamically stable with a positive capacity. In the canonical ensemble, the combination turns out to be k +c<SUB>2</SUB>m<SUP>2</SUP> in the four-dimensional case. When it is positive, a first-order phase transition can happen between small and large black holes if the charge is less than its critical value. In the higher-dimensional [(n +2 )≥5 ] case, even when the charge is absent, the small/large black hole phase transition can also appear, and the coefficients for the third (c<SUB>3</SUB>m<SUP>2</SUP>) and/or fourth (c<SUB>4</SUB>m<SUP>2</SUP>) terms in the potential associated with the graviton mass in massive gravity can play the same role as that of the charge in the four-dimensional case.

[]

https://arxiv.org/pdf/1409.2369.pdf

2020PhRvL.125n1104P

Gravitational Test beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole

2020-01-01

['-', '-']

[]

The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.

[]

https://arxiv.org/pdf/2010.01055.pdf

2002ApJ...565L..75E

Most Supermassive Black Holes Must Be Rapidly Rotating

2002-01-01

['galaxies active', 'astronomy x rays', 'astrophysics']

[]

We use the integrated spectrum of the X-ray background and quasars' spectral energy distribution to derive the contribution of quasars to the energy output of the universe. We find a lower limit for the energy from accretion onto black holes of 7% of the total luminosity of the universe and probably more, with 15% quite possible. Comparing these values with the masses of black holes in the center of nearby galaxies, we show that the accretion process must be, on average, very efficient: at least 15% of the accreted mass must be transformed into radiated energy. This further implies that most supermassive black holes are rotating rapidly.

[]

https://arxiv.org/pdf/astro-ph/0112413.pdf

2007ApJ...665L..51A

Very High Energy Gamma-Ray Radiation from the Stellar Mass Black Hole Binary Cygnus X-1

2007-01-01

['acceleration', 'stars binaries general', 'gamma rays', 'astronomy x rays', 'astrophysics']

[]

We report on the results from the observations in the very high energy band (VHE; E<SUB>γ</SUB>&gt;=100 GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady γ-ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of γ-ray signals at the 4.0 σ significance level (3.2 σ after trial correction) for 154 minutes of effective on-time (EOT) on September 24 between 20:58 and 23:41 UTC, coinciding with an X-ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster-varying signals within a night resulted in an excess with a significance of 4.9 σ (4.1 σ after trial correction) for 79 minutes EOT between 22:17 and 23:41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X-1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dAdtdE)=(2.3+/-0.6)×10<SUP>-12</SUP>(E/1 TeV)<SUP>-3.2+/-0.6</SUP>. This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X-ray binary.

[]

https://arxiv.org/pdf/0706.1505.pdf

2014NatPh..10..864S

Observation of self-amplifying Hawking radiation in an analogue black-hole laser

2014-01-01

['-', '-']

[]

By a combination of quantum field theory and general relativity, black holes have been predicted to emit Hawking radiation. Observation from an actual black hole is, however, probably extremely difficult, so attention has turned to analogue systems in the search for such radiation. Here, we create a narrow, low density, very low temperature atomic Bose–Einstein condensate, containing an analogue black-hole horizon and an inner horizon, as in a charged black hole. We report the observation of Hawking radiation emitted by this black-hole analogue, which is the output of the black-hole laser formed between the horizons. We also observe the exponential growth of a standing wave between the horizons, which results from interference between the negative-energy partners of the Hawking radiation and the negative-energy particles reflected from the inner horizon. We thus observe self-amplifying Hawking radiation.

[]

https://arxiv.org/pdf/1409.6550.pdf

2008PhRvL.101m1601G

Thermodynamics and Bulk Viscosity of Approximate Black Hole Duals to Finite Temperature Quantum Chromodynamics

2008-01-01

['-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio ζ/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first-order transition, we observe a sharp rise in ζ/s near T<SUB>c</SUB>. For constructions that exhibit a smooth crossover, like QCD does, the rise in ζ/s is more modest. We conjecture that divergences in ζ/s for black hole horizons are related to extrema of the entropy density as a function of temperature.

[]

https://arxiv.org/pdf/0804.1950.pdf

2002ApJ...578L..41G

A 20,000 M<SUB>solar</SUB> Black Hole in the Stellar Cluster G1

2002-01-01

['galaxies', 'galaxies star clusters', 'galaxy globular clusters', 'galaxy globular clusters', 'astrophysics']

[]

We present the detection of a 2.0<SUP>+1.4</SUP><SUB>-0.8</SUB>×10<SUP>4</SUP> M<SUB>solar</SUB> black hole (BH) in the stellar cluster G1 (Mayall II), based on data taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. G1 is one of the most massive stellar clusters in M31. The central velocity dispersion (25 km s<SUP>-1</SUP>) and the measured BH mass of G1 place it on a linear extrapolation of the correlation between BH mass and bulge velocity dispersion established for nearby galaxies. The detection of a BH in this low-mass stellar system suggests that (1) the most likely candidates for seed massive BHs come from stellar clusters, (2) there is a direct link between massive stellar clusters and normal galaxies, and (3) the formation process of both bulges and massive clusters is similar because of their concordance in the M<SUB>•</SUB>-σ relation. Globular clusters in our Galaxy should be searched for central BHs. Based on observations made with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS5-26555.

[]

https://arxiv.org/pdf/astro-ph/0209313.pdf

2007ApJ...656..709P

Massive Perturber-driven Interactions between Stars and a Massive Black Hole

2007-01-01

['black hole physics', 'galaxies nuclei', 'ism clouds', 'galaxy open clusters and associations', 'stars kinematics and dynamics', 'astrophysics']

[]

We study the role of massive perturbers (MPs) in deflecting stars and binaries to almost radial (``loss cone'') orbits, where they pass near the central massive black hole (MBH), interact with it at periapse, and are ultimately destroyed. MPs dominate dynamical relaxation when the ratio of the second moments of the MP and star mass distributions, μ<SUB>2</SUB>≡N<SUB>p</SUB>&lt;M<SUP>2</SUP><SUB>p</SUB>&gt;/N<SUB>*</SUB>&lt;M<SUP>2</SUP><SUB>*</SUB>&gt;, satisfies μ<SUB>2</SUB>&gt;&gt;1. We compile the MP mass function from published observations and show that MPs in the nucleus of the Galaxy (mainly giant molecular clouds), and plausibly in late-type galaxies generally, have 10<SUP>2</SUP>&lt;~μ<SUB>2</SUB>&lt;~10<SUP>8</SUP>. MPs thus shorten the relaxation timescale by 10<SUP>1</SUP>-10<SUP>7</SUP> relative to two-body relaxation by stars alone. We show that this increases by 10<SUP>1</SUP>-10<SUP>3</SUP> the rate of large-periapse interactions with the MBH, where loss cone refilling by stellar two-body relaxation is inefficient. We extend the Fokker-Planck loss cone formalism to approximately account for relaxation by rare encounters with MPs. We show that binary star-MBH exchanges driven by MPs can explain the origin of the young main-sequence B stars that are observed very near the Galactic MBH and can increase by orders of magnitude the ejection rate of hypervelocity stars. In contrast, the rate of small-periapse interactions of single stars with the MBH, such as tidal disruption, is only increased by a factor of a few. We suggest that MP-driven relaxation plays an important role in the three-body exchange capture of stars on very tight orbits around the MBH. These captured stars may later be disrupted by the MBH via tidal orbital decay or direct scattering into the loss cone; captured compact objects may inspiral into the MBH by the emission of gravitational waves from zero-eccentricity orbits.

[]

https://arxiv.org/pdf/astro-ph/0606443.pdf

2011JHEP...11..127B

Exact solutions for supersymmetric stationary black hole composites

2011-01-01

['black hole physics', '-', '-']

[]

Four dimensional mathcal{N} = {2} supergravity has regular, stationary, asymptotically flat BPS solutions with intrinsic angular momentum, describing bound states of separate extremal black holes with mutually nonlocal charges. Though the existence and some properties of these solutions were established some time ago, fully explicit analytic solutions were lacking thus far. In this note, we fill this gap. We show in general that explicit solutions can be constructed whenever an explicit formula is known in the theory at hand for the Bekenstein-Hawking entropy of a single black hole as a function of its charges, and illustrate this with some simple examples. We also give an example of moduli-dependent black hole entropy.

[]

https://arxiv.org/pdf/hep-th/0304094.pdf