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2016CQGra..33e4001Y

Black hole based tests of general relativity

2016-01-01

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

[]

General relativity has passed all solar system experiments and neutron star based tests, such as binary pulsar observations, with flying colors. A more exotic arena for testing general relativity is in systems that contain one or more black holes. Black holes are the most compact objects in the Universe, providing probes of the strongest-possible gravitational fields. We are motivated to study strong-field gravity since many theories give large deviations from general relativity only at large field strengths, while recovering the weak-field behavior. In this article, we review how one can probe general relativity and various alternative theories of gravity by using electromagnetic waves from a black hole with an accretion disk, and gravitational waves from black hole binaries. We first review model-independent ways of testing gravity with electromagnetic/gravitational waves from a black hole system. We then focus on selected examples of theories that extend general relativity in rather simple ways. Some important characteristics of general relativity include (but are not limited to) (i) only tensor gravitational degrees of freedom, (ii) the graviton is massless, (iii) no quadratic or higher curvatures in the action, and (iv) the theory is four-dimensional. Altering a characteristic leads to a different extension of general relativity: (i) scalar-tensor theories, (ii) massive gravity theories, (iii) quadratic gravity, and (iv) theories with large extra dimensions. Within each theory, we describe black hole solutions, their properties, and current and projected constraints on each theory using black hole based tests of gravity. We close this review by listing some of the open problems in model-independent tests and within each specific theory.

[]

https://arxiv.org/pdf/1602.02413.pdf

1997ApJ...487..834T

X-Ray Spectral Formation in a Converging Fluid Flow: Spherical Accretion into Black Holes

1997-01-01

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

[]

We study Compton upscattering of low-frequency photons in a converging flow of thermal plasma. The photons escape diffusively, and electron scattering is the dominant source of opacity. We solve the equation of radiative transfer in the case of spherical, steady state accretion into black holes numerically and approximately analytically. Unlike previous work on this subject, we consider the inner boundary at a finite radius, and this has a significant effect on the emergent spectrum. It is shown that the bulk motion of the converging flow is more efficient in upscattering photons than thermal Comptonization, provided that the electron temperature in the flow is of order a few keV or less. In this case, the spectrum observed at infinity consists of a soft component coming from input photons that escaped after a few scatterings without any significant energy change and of a power law that extends to high energies and is made of those photons that underwent significant upscattering. The luminosity of the power law is relatively small compared to that of the soft component. The more reflective the inner boundary is, the flatter the power-law spectrum becomes. The spectral energy power-law index for black hole accretion is always higher than 1, and it is approximately 1.5 for high accretion rates. This result tempts us to say that bulk motion Comptonization might be the mechanism behind the power-law spectra seen in black hole X-ray sources.

[]

https://arxiv.org/pdf/astro-ph/9702092.pdf

2007MNRAS.377.1711S

The imprint of massive black hole formation models on the LISA data stream

2007-01-01

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

[]

The formation, merging and accretion history of massive black holes (MBHs) along the hierarchical build-up of cosmic structures leaves a unique imprint on the background of gravitational waves (GWs) at mHz frequencies. We study here, by means of dedicated simulations of black hole build-up, the possibility of constraining different models of black hole cosmic evolution using future GW space-borne missions, such as LISA. We consider two main scenarios for black hole formation, namely, one where seeds are light (~=10<SUP>2</SUP>M<SUB>solar</SUB>, remnant of Population III stars) and one where seeds are heavy (&gt;~10<SUP>4</SUP>M<SUB>solar</SUB>, direct collapse). In all the models we have investigated, MBH binary coalescences do not produce a stochastic GW background, but rather, a set of individual resolved events. Detection of several hundreds merging events in a 3-yr LISA mission will be the sign of a heavy seed scenario with efficient formation of black hole seeds in a large fraction of high-redshift haloes. At the other extreme, a low event rate, about a few tens in 3 yr, is peculiar of scenarios where either the seeds are light, and many coalescences do not fall into the LISA band, or seeds are massive, but rare. In this case a decisive diagnostic is provided by the shape of the mass distribution of detected events. Light binaries (m &lt; 10<SUP>4</SUP>M<SUB>solar</SUB>) are predicted in a fairly large number in Population III remnant models, but are totally absent in direct collapse models. Finally, a further, helpful diagnostic of black hole formation models lies in the distribution of the mass ratios in binary coalescences. While heavy seed models predict that most of the detected events involve equal-mass binaries, in the case of light seeds, mass ratios are equally distributed in the range 0.1-1.

[]

https://arxiv.org/pdf/astro-ph/0701556.pdf

1994MNRAS.269..199H

Low-Frequency Gravitational Waves from Supermassive Black-Holes

1994-01-01

['astrophysics']

[]

Supermassive black holes are investigated as possible sources for low-frequency bursts of gravitational waves. The event rate for `known' supermassive black holes at intermediate and high red shifts, inferred from the quasar luminosity function, is low, 0.1yr . A number density of gravitational wave sources, which is comparable to the number density of galaxies inferred from faint galaxy counts, is necessary to raise the event rate significantly above one per year. A space-based interferometer could therefore only see several events per year from supermassive black holes if an additional population of supermassive black holes existed and emitted gravitational waves efficiently. These might reside in the population of dwarf galaxies, or in a transient population of small dark-matter haloes that have, for the most part, merged into larger haloes hosting the galaxies seen today, as proposed in a hierarchical cosmogony. In the latter case, event rates could be of the order of 10-1000 per year, due to coalescing supermassive-biack-hole binaries formed during the merging process. Event rates could be as high as a few per second if the dark matter in galactic haloes consisted of supermassive black holes in the mass range M0, and produced gravitational waves efficiently. The proposed space-based gravitational wave interferometer LISA/SAGITTARIUS should detect most gravitational wave events involving supermassive black holes above 10 M0, out to redshifts of z 100. Key words: black hole physics - gravitation - radiation mechanisms: non-thermal - relativity - cosmology: theory - dark matter.

[]

https://arxiv.org/pdf/astro-ph/9405032.pdf

2010PhRvD..81h4024B

Improved effective-one-body Hamiltonian for spinning black-hole binaries

2010-01-01

['-', '-', '-', '-', 'methods numerical', 'methods numerical', '-', 'perturbation theory', '-', '-', '-', '-', '-']

[]

Building on a recent paper in which we computed the canonical Hamiltonian of a spinning test particle in curved spacetime, at linear order in the particle’s spin, we work out an improved effective-one-body (EOB) Hamiltonian for spinning black-hole binaries. As in previous descriptions, we endow the effective particle not only with a mass μ, but also with a spin S<SUB>*</SUB>. Thus, the effective particle interacts with the effective Kerr background (having spin S<SUB>Kerr</SUB>) through a geodesic-type interaction and an additional spin-dependent interaction proportional to S<SUB>*</SUB>. When expanded in post-Newtonian orders, the EOB Hamiltonian reproduces the leading order spin-spin coupling and the spin-orbit coupling through 2.5 post-Newtonian order, for any mass ratio. Also, it reproduces all spin-orbit couplings in the test-particle limit. Similarly to the test-particle limit case, when we restrict the EOB dynamics to spins aligned or antialigned with the orbital angular momentum, for which circular orbits exist, the EOB dynamics has several interesting features, such as the existence of an innermost stable circular orbit, a photon circular orbit, and a maximum in the orbital frequency during the plunge subsequent to the inspiral. These properties are crucial for reproducing the dynamics and gravitational-wave emission of spinning black-hole binaries, as calculated in numerical relativity simulations.

[]

https://arxiv.org/pdf/0912.3517.pdf

2011JHEP...07..115D

Black holes with only one Killing field

2011-01-01

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

[]

We present the first examples of black holes with only one Killing field. The solutions describe five dimensional AdS black holes with scalar hair. The black holes are neither stationary nor axisymmetric, but are invariant under a single Killing field which is tangent to the null generators of the horizon. Some of these solutions can be viewed as putting black holes into rotating boson stars. Others are related to the endpoint of a superradiant instability. For given mass and angular momentum (within a certain range) several black hole solutions exist.

[]

https://arxiv.org/pdf/1105.4167.pdf

2001PhRvD..64d4005R

Classical and thermodynamic stability of black branes

2001-01-01

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

[]

It is argued that many nonextremal black branes exhibit a classical Gregory-Laflamme instability if, and only if, they are locally thermodynamically unstable. For some black branes, the Gregory-Laflamme instability must therefore disappear near extremality. For the black p-branes of the type II supergravity theories, the Gregory-Laflamme instability disappears near extremality for p=1,2,4 but persists all the way down to extremality for p=5,6 (the black D3-brane is not covered by the analysis of this paper). This implies that the instability also vanishes for the near-extremal black M2 and M5-brane solutions.

[]

https://arxiv.org/pdf/hep-th/0104071.pdf

2002MNRAS.335..517V

A SAURON study of M32: measuring the intrinsic flattening and the central black hole mass

2002-01-01

['methods data analysis', 'techniques spectroscopic', 'galaxies elliptical lenticular;cd', 'cd', 'galaxies', 'galaxies kinematics and dynamics', 'galaxies structure', 'astrophysics']

[]

We present dynamical models of the nearby compact elliptical galaxy M32, using high-quality kinematic measurements, obtained with the integral-field spectrograph SAURON mounted on the William Herschel Telescope on La Palma. We also include STIS data obtained previously by Joseph et al. We find a best-fitting black hole mass of M<SUB>•</SUB>= (2.5 +/- 0.5) × 10<SUP>6</SUP> M<SUB>solar</SUB> and a stellar I-band mass-to-light ratio of (1.85 +/- 0.15) M<SUB>solar</SUB>/L<SUB>solar</SUB>. For the first time, we are also able to constrain the inclination along which M32 is observed to 70°+/- 5°. Assuming that M32 is indeed axisymmetric, the averaged observed flattening of 0.73 then corresponds to an intrinsic flattening of 0.68 +/- 0.03. These tight constraints are mainly caused by the use of integral-field data. We show this quantitatively by comparing with models that are constrained by multiple slits only. We show the phase-space distribution and intrinsic velocity structure of the best-fitting model and investigate the effect of regularization on the orbit distribution.

[]

https://arxiv.org/pdf/astro-ph/0201086.pdf

2008MNRAS.386...65M

Black holes and core expansion in massive star clusters

2008-01-01

['stars kinematics and dynamics', 'methods n body', 'clusters globular', 'galaxies magellanic clouds', 'astrophysics']

[]

In this study we present the results from realistic N-body modelling of massive star clusters in the Magellanic Clouds. We have computed eight simulations with N ~ 10<SUP>5</SUP> particles; six of these were evolved for at least a Hubble time. The aim of this modelling is to examine in detail the possibility of large-scale core expansion in massive star clusters, and search for a viable dynamical origin for the radius-age trend observed for such objects in the Magellanic Clouds. We identify two physical processes which can lead to significant and prolonged cluster core expansion - mass-loss due to rapid stellar evolution in a primordially mass-segregated cluster, and heating due to a retained population of stellar mass black holes, formed in the supernova explosions of the most massive cluster stars. These two processes operate over different time-scales and during different periods of a cluster's life. The former occurs only at early times and cannot drive core expansion for longer than a few hundred Myr, while the latter typically does not begin until several hundred Myr have passed, but can result in core expansion lasting for many Gyr. We investigate the behaviour of each of these expansion mechanisms under different circumstances - in clusters with varying degrees of primordial mass segregation, and in clusters with varying black hole retention fractions. In combination, the two processes can lead to a wide variety of evolutionary paths on the radius-age plane, which fully cover the observed cluster distribution and hence define a dynamical origin for the radius-age trend in the Magellanic Clouds. We discuss in some detail the implications of core expansion for various aspects of globular cluster research, as well as the possibility of observationally inferring the presence of a significant population of stellar mass black holes in a cluster.

[]

https://arxiv.org/pdf/0802.0513.pdf

2012PhRvD..85b4037K

Tidal-disruption rate of stars by spinning supermassive black holes

2012-01-01

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

[]

A supermassive black hole can disrupt a star when its tidal field exceeds the star’s self-gravity, and can directly capture stars that cross its event horizon. For black holes with mass M≳10<SUP>7</SUP>M<SUB>⊙</SUB>, tidal disruption of main-sequence stars occurs close enough to the event horizon that a Newtonian treatment of the tidal field is no longer valid. The fraction of stars that are directly captured is also no longer negligible. We calculate generically oriented stellar orbits in the Kerr metric, and evaluate the relativistic tidal tensor at the pericenter for those stars not directly captured by the black hole. We combine this relativistic analysis with previous calculations of how these orbits are populated to determine tidal-disruption rates for spinning black holes. We find, consistent with previous results, that black-hole spin increases the upper limit on the mass of a black hole capable of tidally disrupting solarlike stars to ∼7×10<SUP>8</SUP>M<SUB>⊙</SUB>. More quantitatively, we find that direct stellar capture reduces tidal-disruption rates by a factor ∼2/3(1/10) at M≃10<SUP>7</SUP>(10<SUP>8</SUP>)M<SUB>⊙</SUB>. The strong dependence of tidal-disruption rates on black-hole spin for M≳10<SUP>8</SUP>M<SUB>⊙</SUB> implies that future surveys like the Large Synoptic Survey Telescope that discover thousands of tidal-disruption events can constrain supermassive black-hole spin demographics.

[]

https://arxiv.org/pdf/1109.6329.pdf

2015MNRAS.447...49S

Global simulations of axisymmetric radiative black hole accretion discs in general relativity with a mean-field magnetic dynamo

2015-01-01

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

[]

We present a mean-field model that emulates the magnetic dynamo operating in magnetized accretion discs. We have implemented this model in the general relativisic radiation magnetohydrodynamic (GRRMHD) code KORAL, using results from local shearing sheet simulations of the magnetorotational instability to fix the parameters of the dynamo. With the inclusion of this dynamo, we are able to run 2D axisymmetric GRRMHD simulations of accretion discs for arbitrarily long times. The simulated discs exhibit sustained turbulence, with the poloidal and toroidal magnetic field components driven towards a state similar to that seen in 3D studies. Using this dynamo code, we present a set of long-duration global simulations of super-Eddington, optically thick discs around non-spinning and spinning black holes. Super-Eddington discs around non-rotating black holes exhibit a surprisingly large efficiency, η ≈ 0.04, independent of the accretion rate, where we measure efficiency in terms of the total energy output, both radiation and mechanical, flowing out to infinity. This value significantly exceeds the efficiency predicted by slim disc models for these accretion rates. Super-Eddington discs around spinning black holes are even more efficient, and appear to extract black hole rotational energy through a process similar to the Blandford-Znajek mechanism. All the simulated models are characterized by highly super-Eddington radiative fluxes collimated along the rotation axis. We also present a set of simulations that were designed to have Eddington or slightly sub-Eddington accretion rates (dot{M} ≲ 2dot{M}_Edd). None of these models reached a steady state. Instead, the discs collapsed as a result of runaway cooling, presumably because of a thermal instability.

[]

https://arxiv.org/pdf/1407.4421.pdf

2019NewAR..8601525D

The quest for dual and binary supermassive black holes: A multi-messenger view

2019-01-01

['galaxies active', 'galaxies interactions', 'galaxies nuclei', 'galaxies quasars', 'gravitational waves', '-', '-']

[]

The quest for binary and dual supermassive black holes (SMBHs) at the dawn of the multi-messenger era is compelling. Detecting dual active galactic nuclei (AGN) - active SMBHs at projected separations larger than several parsecs - and binary AGN - probing the scale where SMBHs are bound in a Keplerian binary - is an observational challenge. The study of AGN pairs (either dual or binary) also represents an overarching theoretical problem in cosmology and astrophysics. The AGN triggering calls for detailed knowledge of the hydrodynamical conditions of gas in the imminent surroundings of the SMBHs and, at the same time, their duality calls for detailed knowledge on how galaxies assemble through major and minor mergers and grow fed by matter along the filaments of the cosmic web. This review describes the techniques used across the electromagnetic spectrum to detect dual and binary AGN candidates and proposes new avenues for their search. The current observational status is compared with the state-of-the-art numerical simulations and models for formation of dual and binary AGN. Binary SMBHs are among the loudest sources of gravitational waves (GWs) in the Universe. The search for a background of GWs at nHz frequencies from inspiralling SMBHs at low redshifts, and the direct detection of signals from their coalescence by the Laser Interferometer Space Antenna in the next decade, make this a theme of major interest for multi-messenger astrophysics. This review discusses the future facilities and observational strategies that are likely to significantly advance this fascinating field.

[]

https://arxiv.org/pdf/2001.06293.pdf

2019ApJ...885L..33N

The Shadow of a Spherically Accreting Black Hole

2019-01-01

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

[]

We explore a simple spherical model of optically thin accretion on a Schwarzschild black hole, and study the properties of the image as seen by a distant observer. We show that a dark circular region in the center—a shadow—is always present. The outer edge of the shadow is located at the photon ring radius {b}<SUB>ph</SUB>}\equiv \sqrt{27}{r}<SUB>g</SUB>, where {r}<SUB>g</SUB>={GM}/{c}<SUP>2</SUP> is the gravitational radius of the accreting mass M. The location of the shadow edge is independent of the inner radius at which the accreting gas stops radiating. The size of the observed shadow is thus a signature of the spacetime geometry and it is hardly influenced by accretion details. We briefly discuss the relevance of these results for the Event Horizon Telescope image of the supermassive black hole in M87.

[]

https://arxiv.org/pdf/1910.02957.pdf

2015PhRvD..92d4028K

Dynamical mass ejection from black hole-neutron star binaries

2015-01-01

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

[]

We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study the dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10°-20° and often sweeps out only a half of the plane. The ejecta mass can be as large as ∼0.1 M<SUB>⊙</SUB>, and the velocity is subrelativistic with ∼0.2 - 0.3 c for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) is larger, and the ejecta velocity is larger, for larger values of the binary mass ratio, i.e., for larger values of the black-hole mass. The remnant black hole-disk system receives a kick velocity of O (100 ) km s<SUP>-1</SUP> due to the ejecta linear momentum, and this easily dominates the kick velocity due to gravitational radiation. Structures of postmerger material, velocity distribution of the dynamical ejecta, fallback rates, and gravitational waves are also investigated. We also discuss the effect of ejecta anisotropy on electromagnetic counterparts, specifically a macronova/kilonova and synchrotron radio emission, developing analytic models.

[]

https://arxiv.org/pdf/1502.05402.pdf

2010Sci...329..927P

Dual Jets from Binary Black Holes

2010-01-01

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

[]

Supermassive black holes are found at the centers of most galaxies and their inspiral is a natural outcome when galaxies merge. The inspiral of these systems is of utmost astrophysical importance as prodigious producers of gravitational waves and in their possible role in energetic electromagnetic events. We study such binary black hole coalescence under the influence of an external magnetic field produced by the expected circumbinary disk surrounding them. Solving the Einstein equations to describe the spacetime and using the force-free approach for the electromagnetic fields and the tenuous plasma, we present numerical evidence for possible jets driven by these systems. Extending the process described by Blandford and Znajek for a single spinning black hole, the picture that emerges suggests the electromagnetic field extracts energy from the orbiting black holes, which ultimately merge and settle into the standard Blandford-Znajek scenario. Emissions along dual and single jets would be expected that could be observable to large distances.

[]

https://arxiv.org/pdf/1005.1067.pdf

2016PhRvD..94f3530G

Microlensing and dynamical constraints on primordial black hole dark matter with an extended mass function

2016-01-01

['-', '-']

[]

The recent discovery of gravitational waves from mergers of ∼10 M<SUB>⊙</SUB> black hole binaries has stimulated interested in primordial black hole (PBH) dark matter in this mass range. Microlensing and dynamical constraints exclude all of the dark matter in compact objects with a delta function mass function in the range 10<SUP>-7</SUP>≲M /M<SUB>⊙</SUB>≲1 0<SUP>5</SUP> . However it has been argued that all of the dark matter could be composed of compact objects in this range with an extended mass function. We explicitly recalculate the microlensing and dynamical constraints for compact objects with an extended mass function which replicates the PBH mass function produced by inflation models. We find that the microlensing and dynamical constraints place conflicting constraints on the width of the mass function, and do not find a mass function which satisfies both constraints.

[]

https://arxiv.org/pdf/1609.01143.pdf

1993PhRvD..47.2242G

Eluding the no-hair conjecture: Black holes in spontaneously broken gauge theories

1993-01-01

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

[]

We study regular and black hole solutions to the coupled classical Einstein-Yang-Mills-Higgs system. It has long been thought that black hole solutions in the spontaneously broken phase of such a theory could have no nontrivial field structure outside of the horizon. We first show that the standard black hole no-hair theorem underlying this belief, although true in the Abelian setting, does not necessarily extend to the non-Abelian case. This indicates the possibility of solutions with nontrivial gauge and Higgs configurations decaying exponentially outside the horizon. We then find such solutions by numerical integration of the classical equations for the case of SU(2) coupled to a Higgs doublet (the standard model less hypercharge). As a prelude to this work we also study regular and black hole solutions to Einstein-non-Abelian-Proca theory and as a postscript we briefly discuss the important issue of stability.

[]

https://arxiv.org/pdf/hep-th/9211007.pdf

1997PhRvD..55.7423B

Non-Gaussian fluctuations and primordial black holes from inflation

1997-01-01

['-', '-', '-', '-', 'particles', 'black hole physics', 'background', 'astrophysics', '-', '-']

[]

We explore the role of non-Gaussian fluctuations in primordial black hole (PBH) formation and show that the standard Gaussian assumption, used in all PBH formation papers to date, is not justified. Since large spikes in power are usually associated with flat regions of the inflaton potential, quantum fluctuations become more important in the field dynamics, leading to mode-mode coupling and non-Gaussian statistics. Moreover, PBH production requires several σ (rare) fluctuations in order to prevent premature matter dominance of the universe, so we are necessarily concerned with distribution tails, where any intrinsic skewness will be especially important. We quantify this argument by using the stochastic slow-roll equation and a relatively simple analytic method to obtain the final distribution of fluctuations. We work out several examples with toy models that produce PBH's, and test the results with numerical simulations. Our examples show that the naive Gaussian assumption can result in errors of many orders of magnitude. For models with spikes in power, our calculations give sharp cutoffs in the probability of large positive fluctuations, meaning that Gaussian distributions would vastly overproduce PBH's. The standard results that link inflation-produced power spectra and PBH number densities must then be reconsidered, since they rely quite heavily on the Gaussian assumption. We point out that since the probability distributions depend strongly on the nature of the potential, it is impossible to obtain results for general models. However, calculating the distribution of fluctuations for any specific model seems to be relatively straightforward, at least in the single inflaton case.

[]

https://arxiv.org/pdf/astro-ph/9611106.pdf

1995PhRvD..52.3518J

Increase of black hole entropy in higher curvature gravity

1995-01-01

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

[]

We examine the zeroth law and the second law of black hole thermodynamics within the context of effective gravitational actions including higher curvature interactions. We show that entropy can never decrease for quasistationary processes in which a black hole accretes positive energy matter, independent of the details of the gravitational action. Within a class of higher curvature theories where the Lagrangian consists of a polynomial in the Ricci scalar, we use a conformally equivalent theory to establish that stationary black hole solutions with a Killing horizon satisfy the zeroth law, and that the second law holds in general for any dynamical process. We also introduce a new method for establishing the second law based on a generalization of the area theorem, which may prove useful for a wider class of Lagrangians. Finally, we show how one can infer the form of the black hole entropy, at least for the Ricci polynomial theories, by integrating the changes of mass and angular momentum in a quasistationary accretion process.

[]

https://arxiv.org/pdf/gr-qc/9503020.pdf

1998ApJ...499..315T

Mechanisms for High-Frequency Quasi-periodic Oscillations in Neutron Star and Black Hole Binaries

1998-01-01

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

[]

We explain the millisecond variability detected by Rossi X-Ray Timing Explorer (RXTE) in the X-ray emission from a number of low-mass X-ray binary systems (Sco X-1, 4U 1728-34, 4U 1608-522, 4U 1636-536, 4U 0614+091, 4U 1735-44, 4U 1820-30, GX 5-1) in terms of dynamics of the centrifugal barrier, a hot boundary region surrounding a neutron star (NS). We demonstrate that this region may experience the relaxation oscillations and that the displacements of a gas element both in radial and vertical directions occur at the same main frequency, of order of the local Keplerian frequency. We show the importance of the effect of a splitting of the main frequency produced by the Coriolis force in a rotating disk for the interpretation of a spacing between the quasi-periodic oscillation (QPO) peaks. We estimate a magnitude of the splitting effect and present a simple formula for the whole spectrum of the split frequencies. It is interesting that the first three lowest order overtones (corresponding to the azimuthal numbers m = 0, -1, and -2) fall in the range of 200-1200 Hz and match the kHz QPO frequencies observed by RXTE. Similar phenomena should also occur in black hole (BH) systems, but, since the QPO frequency is inversely proportional to the mass of a compact object, the frequency of the centrifugal-barrier oscillations in the BH systems should be a factor of 5-10 lower than that for the NS systems. The X-ray spectrum formed in this region is a result of upscattering of a soft radiation (from a disk and an NS surface) off relatively hot electrons in the boundary layer. The typical size of the emission region should be 1-3 km, which is consistent with the time-lag measurements. We also briefly discuss some alternative QPO models, including the possibility of acoustic oscillations in the boundary layer, the proper stellar rotation, and g-mode disk oscillations.

[]

https://arxiv.org/pdf/astro-ph/9712348.pdf

2002PhRvD..66d4005S

Fate of the first traversible wormhole: Black-hole collapse or inflationary expansion

2002-01-01

['-', '-', '-', '-', '-', 'methods numerical', '-', 'particles', '-']

[]

We study numerically the stability of the first Morris-Thorne traversible wormhole, shown previously by Ellis to be a solution for a massless ghost Klein-Gordon field. Our code uses a dual-null formulation for spherically symmetric space-time integration, and the numerical range covers both universes connected by the wormhole. We observe that the wormhole is unstable against Gaussian pulses in either exotic or normal massless Klein-Gordon fields. The wormhole throat suffers a bifurcation of horizons and either explodes to form an inflationary universe or collapses to a black hole if the total input energy, is, respectively, negative or positive. As the perturbations become small in total energy, there is evidence for critical solutions with a certain black-hole mass or Hubble constant. The collapse time is related to the initial energy with an apparently universal critical exponent. For normal matter, such as a traveller traversing the wormhole, collapse to a black hole always results. However, carefully balanced additional ghost radiation can maintain the wormhole for a limited time. The black-hole formation from a traversible wormhole confirms the recently proposed duality between them. The inflationary case provides a mechanism for inflating, to macroscopic size, a Planck-sized wormhole formed in space-time foam.

[]

https://arxiv.org/pdf/gr-qc/0205041.pdf

2000PhLB..481...79W

Quasinormal modes of Reissner-Nordström Anti-de Sitter black holes

2000-01-01

['-']

[]

Complex frequencies associated with quasinormal modes for large Reissner-Nordström Anti-de Sitter black holes have been computed. These frequencies have close relation to the black hole charge and do not linearly scale with the black hole temperature as in Schwarzschild Anti-de Sitter case. In terms of AdS/CFT correspondence, we found that the bigger the black hole charge is, the quicker for the approach to thermal equilibrium in the CFT. The properties of quasinormal modes for /l&gt;0 have also been studied.

[]

https://arxiv.org/pdf/hep-th/0003295.pdf

2014PhRvD..90h2004D

Implementing a search for aligned-spin neutron star-black hole systems with advanced ground based gravitational wave detectors

2014-01-01

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

[]

We study the effect of spins on searches for gravitational waves from compact binary coalescences in realistic simulated early advanced LIGO data. We construct a detection pipeline including matched filtering, signal-based vetoes, a coincidence test between different detectors, and an estimate of the rate of background events. We restrict attention to neutron star-black hole (NS-BH) binary systems, and we compare a search using nonspinning templates to one using templates that include spins aligned with the orbital angular momentum. To run the searches we implement the binary inspiral matched-filter computation in PyCBC, a new software toolkit for gravitational-wave data analysis. We find that the inclusion of aligned-spin effects significantly increases the astrophysical reach of the search. Considering astrophysical NS-BH systems with nonprecessing black hole spins, for dimensionless spin components along the orbital angular momentum uniformly distributed in (-1,1), the sensitive volume of the search with aligned-spin templates is increased by ∼50% compared to the nonspinning search; for signals with aligned spins uniformly distributed in the range (0.7,1), the increase in sensitive volume is a factor of ∼10.

[]

https://arxiv.org/pdf/1405.6731.pdf

2008CMaPh.283..749H

Uniqueness Theorem for 5-Dimensional Black Holes with Two Axial Killing Fields

2008-01-01

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

[]

We show that two stationary, asymptotically flat vacuum black holes in 5 dimensions with two commuting axial symmetries are identical if and only if their masses, angular momenta, and their "interval structures" coincide. We also show that the horizon must be topologically either a 3-sphere, a ring, or a Lens-space. Our argument is a generalization of constructions of Morisawa and Ida (based in turn on key work of Maison) who considered the spherical case, combined with basic arguments concerning the nature of the factor manifold of symmetry orbits.

[]

https://arxiv.org/pdf/0707.2775.pdf

2002MNRAS.331..805H

Untangling the merger history of massive black holes with LISA

2002-01-01

['black hole physics', 'gravitation', 'gravitational waves', 'cosmology miscellaneous', 'astrophysics', '-']

[]

Binary black hole coalescences emit gravitational waves that will be measurable by the space-based detector LISA to large redshifts. This suggests that LISA may be able to observe black holes grow and evolve as the Universe evolves, mapping the distribution of black hole masses as a function of redshift. An immediate difficulty with this idea is that LISA measures certain redshifted combinations of masses with good accuracy: if a system has some mass parameter m , then LISA measures (1+z )m . This mass-redshift degeneracy makes it difficult to follow the mass evolution. In many cases, LISA will also measure the luminosity distance D of a coalescence accurately. Since cosmological parameters (particularly the mean density, the cosmological constant and the Hubble constant) are now known with moderate precision, we can obtain z from D and break the degeneracy. This makes it possible to untangle the mass and redshift and to study the mass and merger history of black holes. Mapping the black hole mass distribution could open a window on to an early epoch of structure formation.

[]

https://arxiv.org/pdf/astro-ph/0108483.pdf

2005ApJ...620..905Y

An Accretion-Jet Model for Black Hole Binaries: Interpreting the Spectral and Timing Features of XTE J1118+480

2005-01-01

['accretion', 'accretion disks', 'black hole physics', 'ism jets and outflows', '-', 'astronomy x rays', 'astrophysics']

[]

Multiwavelength observations of the black hole X-ray binary XTE J1118+480 have offered abundant spectral and timing information about the source and have thus provided serious challenges to theoretical models. We propose a coupled accretion-jet model to interpret the observations. We model the accretion flow as an outer standard thin accretion disk truncated at a transition radius by an inner hot accretion flow. The accretion flow accounts for the observed UV and X-ray emission, but it substantially underpredicts the radio and infrared fluxes, even after we allow for nonthermal electrons in the hot flow. We attribute the latter components to a jet. We model the jet emission by means of the internal shock scenario, which is widely employed for gamma-ray bursts. In our accretion-jet model of XTE J1118+480, the jet dominates the radio and infrared emission, the thin disk dominates the UV emission, and the hot flow produces most of the X-ray emission. The optical emission has contributions from all three components: jet, thin disk, and hot flow. The model qualitatively accounts for timing features, such as the intriguing positive and negative time lags between the optical and X-ray emission and the wavelength-dependent variability amplitude.

[]

https://arxiv.org/pdf/astro-ph/0407612.pdf

2008ApJ...682L..29B

Modeling Kicks from the Merger of Generic Black Hole Binaries

2008-01-01

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

[]

Recent numerical relativistic results demonstrate that the merger of comparable-mass spinning black holes has a maximum "recoil kick" of up to ~4000 km s<SUP>-1</SUP>. However, the scaling of these recoil velocities with mass ratio is poorly understood. We present new runs showing that the maximum possible kick perpendicular to the orbital plane does not scale as ~η<SUP>2</SUP> (where η is the symmetric mass ratio), as previously proposed, but is more consistent with ~η<SUP>3</SUP>, at least for systems with low orbital precession. We discuss the effect of this dependence on galactic ejection scenarios and retention of intermediate-mass black holes in globular clusters.

[]

https://arxiv.org/pdf/0802.0416.pdf

2007ApJ...669...45H

A Theoretical Interpretation of the Black Hole Fundamental Plane

2007-01-01

['cosmology theory', 'galaxies active', 'galaxies evolution', 'galaxies quasars', 'astrophysics']

[]

We examine the origin and evolution of correlations between properties of supermassive BHs and their host galaxies using simulations of major galaxy mergers, including the effects of gas dissipation, cooling, star formation, and BH accretion and feedback. We demonstrate that the simulations predict the existence of a BH ``fundamental plane'' (BHFP), of the form M<SUB>BH</SUB>~σ<SUP>3.0+/-0.3</SUP>R<SUP>0.43+/-0.19</SUP><SUB>e</SUB> or M<SUB>BH</SUB>~M<SUP>0.54+/-0.17</SUP><SUB>*</SUB>σ<SUP>2.2+/-0.5</SUP>, similar to relations found observationally. The simulations indicate that the BHFP can be understood roughly as a tilted intrinsic correlation between BH mass and spheroid binding energy, or the condition for feedback coupling to power a pressure-driven outflow. While changes in halo circular velocity, merger orbital parameters, progenitor disk redshifts and gas fractions, ISM gas pressurization, and other parameters can drive changes in, e.g., σ at fixed M<SUB>*</SUB>, and therefore changes in the M<SUB>BH</SUB>-σ or M<SUB>BH</SUB>-M<SUB>*</SUB> relations, the BHFP is robust. Given the empirical trend of decreasing R<SUB>e</SUB> for a given M<SUB>*</SUB> at high redshift (i.e., increasingly deep potential wells), the BHFP predicts that BHs will be more massive at fixed M<SUB>*</SUB>, in good agreement with recent observations. This evolution in the structural properties of merger remnants, to smaller R<SUB>e</SUB> and larger σ (and therefore larger M<SUB>BH</SUB>, conserving the BHFP) at a given M<SUB>*</SUB>, is driven by the fact that disks (merger progenitors) have characteristically larger gas fractions at high redshifts. Adopting the observed evolution of disk gas fractions with redshift, our simulations predict the observed trends in both R<SUB>e</SUB>(M<SUB>*</SUB>) and M<SUB>BH</SUB>(M<SUB>*</SUB>). The existence of this BHFP also has important implications for the masses of the very largest black holes and immediately resolves several apparent conflicts between the BH masses expected and measured for outliers in both the M<SUB>BH</SUB>-σ and M<SUB>BH</SUB>-M<SUB>*</SUB> relations.

[]

https://arxiv.org/pdf/astro-ph/0701351.pdf

2007CQGra..24R...1H

TOPICAL REVIEW: Instabilities of black strings and branes

2007-01-01

['-', '-']

[]

We review recent progress on the instabilities of black strings and branes both for pure Einstein gravity as well as supergravity theories which are relevant for string theory. We focus mainly on Gregory Laflamme instabilities. In the first part of the review, we provide a detailed discussion of the classical gravitational instability of the neutral uniform black string in higher-dimensional gravity. The uniform black string is part of a larger phase diagram of Kaluza Klein black holes which will be discussed thoroughly. This phase diagram exhibits many interesting features including new phases, non-uniqueness and horizon-topology changing transitions. In the second part, we turn to charged black branes in supergravity and show how the Gregory Laflamme instability of the neutral black string implies via a boost/U-duality map similar instabilities for non- and near-extremal smeared branes in string theory. We also comment on instabilities of D-brane bound states. The connection between classical and thermodynamic stability, known as the correlated stability conjecture, is also reviewed and illustrated with examples. Finally, we examine the holographic implications of the Gregory Laflamme instability for a number of non-gravitational theories including Yang Mills theories and little string theory.

[]

https://arxiv.org/pdf/hep-th/0701022.pdf

2004MNRAS.349...68B

Two-dimensional adiabatic flows on to a black hole - I. Fluid accretion

2004-01-01

['accretion', 'accretion disks', 'black hole physics', 'hydrodynamics', 'galaxies quasars', 'astrophysics']

[]

When gas accretes on to a black hole, at a rate either much less than or much greater than the Eddington rate, it is likely to do so in an `adiabatic' or radiatively inefficient manner. Under fluid (as opposed to magnetohydrodynamic) conditions, the disc should become convective and evolve toward a state of marginal instability. We model the resulting disc structure as `gyrentropic', with convection proceeding along common surfaces of constant angular momentum, Bernouilli function and entropy, called `gyrentropes'. We present a family of two-dimensional, self-similar models that describes the time-averaged disc structure. We then suppose that there is a self-similar, Newtonian torque, which dominates the angular momentum transport and that the Prandtl number is large so that convection dominates the heat transport. The torque drives inflow and meridional circulation and the resulting flow is computed. Convective transport will become ineffectual near the disc surface. It is conjectured that this will lead to a large increase of entropy across a `thermal front', which we identify as the effective disc surface and the base of an outflow. The conservation of mass, momentum and energy across this thermal front permits a matching of the disc models to self-similar outflow solutions. We then demonstrate that self-similar disc solutions can be matched smoothly on to relativistic flows at small radius and thin discs at large radius. This model of adiabatic accretion is contrasted with some alternative models that have been discussed recently. The disc models developed in this paper should be useful for interpreting numerical, fluid dynamical simulations. Related principles to those described here may govern the behaviour of astrophysically relevant, magnetohydrodynamic disc models.

[]

https://arxiv.org/pdf/astro-ph/0306184.pdf

2018MNRAS.478.2576M

Intermediate-mass black holes in dwarf galaxies out to redshift ∼2.4 in the Chandra COSMOS-Legacy Survey

2018-01-01

['galaxies active', 'galaxies dwarf', 'galaxies starburst', 'astronomy x rays', '-']

[]

We present a sample of 40 active galactic nucleus (AGN) in dwarf galaxies at redshifts z ≲ 2.4. The galaxies are drawn from the Chandra COSMOS-Legacy survey as having stellar masses 10<SUP>7</SUP> ≤ M<SUB>*</SUB> ≤ 3 × 10<SUP>9</SUP> M<SUB>⊙</SUB>. Most of the dwarf galaxies are star forming. After removing the contribution from star formation to the X-ray emission, the AGN luminosities of the 40 dwarf galaxies are in the range L<SUB>0.5-10 keV</SUB> ∼ 10<SUP>39</SUP>-10<SUP>44</SUP> erg s<SUP>-1</SUP>. With 12 sources at z &gt; 0.5, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. The record-holder is cid_1192, at z = 2.39 and with L<SUB>0.5-10 keV</SUB> ∼ 10<SUP>44</SUP> erg s<SUP>-1</SUP>. One of the dwarf galaxies has M<SUB>*</SUB> = 6.6 × 10<SUP>7</SUP> M<SUB>⊙</SUB> and is the least massive galaxy found so far to host an AGN. All the AGN are of type 2 and consistent with hosting intermediate-mass black holes (BHs) with masses ∼10<SUP>4</SUP>-10<SUP>5</SUP> M<SUB>⊙</SUB> and typical Eddington ratios &gt;1 per cent. We also study the evolution, corrected for completeness, of AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to z = 0.7. We find that the AGN fraction for 10<SUP>9</SUP> &lt; M<SUB>*</SUB> ≤ 3 × 10<SUP>9</SUP> M<SUB>⊙</SUB> and L<SUB>X</SUB> ∼ 10<SUP>41</SUP>-10<SUP>42</SUP> erg s<SUP>-1</SUP> is ∼0.4 per cent for z ≤ 0.3 and that it decreases with X-ray luminosity and decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to decrease with redshift, suggesting that AGN in dwarf galaxies evolve differently than those in high-mass galaxies. Mindful of potential caveats, the results seem to favour a direct collapse formation mechanism for the seed BHs in the early Universe.

[]

https://arxiv.org/pdf/1802.01567.pdf

2005PhRvD..72d1901C

Five-dimensional gauged supergravity black holes with independent rotation parameters

2005-01-01

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

[]

We construct new nonextremal rotating black hole solutions in SO(6) gauged five-dimensional supergravity. Our solutions are the first such examples in which the two rotation parameters are independently specifiable, rather than being set equal. The black holes carry charges for all three of the gauge fields in the U(1)<SUP>3</SUP> subgroup of SO(6), albeit with only one independent charge parameter. We discuss the BPS limits, showing that these include the first examples of regular supersymmetric black holes with independent angular momenta in gauged supergravity. We also find nonsingular BPS solitons. Finally, we obtain another independent class of new rotating nonextremal black hole solutions with just one nonvanishing rotation parameter, and one nonvanishing charge.

[]

https://arxiv.org/pdf/hep-th/0505112.pdf

2020JCAP...03..029E

The exponential tail of inflationary fluctuations: consequences for primordial black holes

2020-01-01

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

[]

The curvature perturbations produced during an early era of inflation are known to have quasi-Gaussian distribution functions close to their maximum, where they are well constrained by measurements of the cosmic microwave background anisotropies and of the large-scale structures. In contrast, the tails of these distributions are poorly known, although this part is the relevant one for rare, extreme objects such as primordial black holes. We show that these tails are highly non-Gaussian, and cannot be described with standard non-Gaussian expansions, that are designed to approximate the distributions close to their maximum only. Using the stochastic-δ N formalism, we develop a generic framework to compute the tails, which are found to have an exponential, rather than Gaussian, decay. These exponential tails are inevitable, and do not require any non-minimal feature as they simply result from the quantum diffusion of the inflaton field along its potential. We apply our formalism to a few relevant single-field, slow-roll inflationary potentials, where our analytical treatment is confirmed by comparison with numerical results. We discuss the implications for the expected abundance of primordial black holes in these models, and highlight that it can differ from standard results by several orders of magnitude. In particular, we find that potentials with an inflection point overproduce primordial black holes, unless slow roll is violated.

[]

https://arxiv.org/pdf/1912.05399.pdf

2019PASA...36...27W

Titans of the early Universe: The Prato statement on the origin of the first supermassive black holes

2019-01-01

['-', 'galaxies quasars', 'high redshift', 'populations', '-', '-', '-', '-', '-']

[]

In recent years, the discovery of massive quasars at has provided a striking challenge to our understanding of the origin and growth of supermassive black holes in the early Universe. Mounting observational and theoretical evidence indicates the viability of massive seeds, formed by the collapse of supermassive stars, as a progenitor model for such early, massive accreting black holes. Although considerable progress has been made in our theoretical understanding, many questions remain regarding how (and how often) such objects may form, how they live and die, and how next generation observatories may yield new insight into the origin of these primordial titans. This review focusses on our present understanding of this remarkable formation scenario, based on the discussions held at the Monash Prato Centre from November 20 to 24, 2017, during the workshop `Titans of the Early Universe: The Origin of the First Supermassive Black Holes'.

[]

https://arxiv.org/pdf/1810.12310.pdf

2007ApJ...669...67H

An Observed Fundamental Plane Relation for Supermassive Black Holes

2007-01-01

['cosmology theory', 'galaxies active', 'galaxies evolution', 'galaxies quasars', 'astrophysics']

[]

We study observed correlations between supermassive black hole (BHs) and the properties of their host galaxies and show that the observations define a BH ``fundamental plane'' (BHFP), of the form M<SUB>BH</SUB>~σ<SUP>3.0+/-0.3</SUP>R<SUP>0.43+/-0.19</SUP><SUB>e</SUB> or M<SUB>BH</SUB>~M<SUP>0.54+/-0.17</SUP><SUB>*</SUB>σ<SUP>2.2+/-0.5</SUP>, analogous to the FP of elliptical galaxies. The BHFP is preferred over a simple relation between M<SUB>BH</SUB> and any of σ, M<SUB>*</SUB>, M<SUB>dyn</SUB>, or R<SUB>e</SUB> alone at &gt;3 σ (99.9%) significance. The existence of this BHFP has important implications for the formation of supermassive BHs and the masses of the very largest black holes and immediately resolves several apparent conflicts between the BH masses expected and measured for outliers in both the M<SUB>BH</SUB>-σ and M<SUB>BH</SUB>-M<SUB>*</SUB> relations.

[]

https://arxiv.org/pdf/0707.4005.pdf

2010PhRvD..81f2002M

Testing properties of the Galactic center black hole using stellar orbits

2010-01-01

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

[]

The spin and quadrupole moment of the supermassive black hole at the Galactic center can in principle be measured via astrometric monitoring of stars orbiting at milliparsec distances, allowing tests of general relativistic “no-hair”theorems . One complicating factor is the presence of perturbations from other stars, which may induce orbital precession of the same order of magnitude as that due to general relativistic effects. The expected number of stars in this region is small enough that full N-body simulations can be carried out. We present the results of a comprehensive set of such simulations, which include a post-Newtonian treatment of spin-orbit effects. A number of possible models for the distribution of stars and stellar remnants are considered. We find that stellar perturbations are likely to obscure the signal due to frame dragging for stars beyond ∼0.5mpc from the black hole, while measurement of the quadrupole moment is likely to require observation of stars inside ∼0.2mpc. A high fraction of stellar remnants, e.g. 10M<SUB>⊙</SUB> black holes, in this region would make tests of general relativity problematic at all radii. We discuss the possibility of separating the effects of stellar perturbations from those due to general relativity.

[]

https://arxiv.org/pdf/0911.4718.pdf

2009MNRAS.398.1392L

Black hole mergers: can gas discs solve the `final parsec' problem?

2009-01-01

['accretion', 'accretion disks', 'black hole physics', 'instabilities', 'hydrodynamics', 'galaxies formation', 'cosmology theory', '-', '-']

[]

We compute the effect of an orbiting gas disc in promoting the coalescence of a central supermassive black hole binary. Unlike earlier studies, we consider a finite mass of gas with explicit time dependence: we do not assume that the gas necessarily adopts a steady state or a spatially constant accretion rate, i.e. that the merging black hole was somehow inserted into a pre-existing accretion disc. We consider the tidal torque of the binary on the disc, and the binary's gravitational radiation. We study the effects of star formation in the gas disc in a simple energy feedback framework. <P />The disc spectrum differs in detail from that found before. In particular, tidal torques from the secondary black hole heat the edges of the gap, creating bright rims around the secondary. These rims do not in practice have uniform brightness either in azimuth or time, but can on average account for as much as 50 per cent of the integrated light from the disc. This may lead to detectable high-photon-energy variability on the relatively long orbital time-scale of the secondary black hole, and thus offer a prospective signature of a coalescing black hole binary. <P />We also find that the disc can drive the binary to merger on a reasonable time-scale only if its mass is at least comparable with that of the secondary black hole, and if the initial binary separation is relatively small, i.e. a<SUB>0</SUB> &lt;~ 0.05 pc. Star formation complicates the merger further by removing mass from the disc. In the feedback model we consider, this sets an effective limit to the disc mass. As a result, binary merging is unlikely unless the black hole mass ratio is &lt;~0.001. Gas discs thus appear not to be an effective solution to the `last parsec' problem for a significant class of mergers.

[]

https://arxiv.org/pdf/0906.0737.pdf

2006ApJ...644L..17W

From Supermassive Black Holes to Dwarf Elliptical Nuclei: A Mass Continuum

2006-01-01

['black hole physics', 'galaxies bulges', 'galaxies dwarf', 'galaxies fundamental parameters', 'galaxies nuclei', 'astrophysics']

[]

Considerable evidence suggests that supermassive black holes reside at the centers of massive galactic bulges. At a lower galactic mass range, many dwarf galaxies contain extremely compact nuclei that structurally resemble massive globular clusters. We show that both these types of central massive objects (CMOs) define a single unbroken relation between CMO mass and the luminosity of their host galaxy spheroid. Equivalently, M<SUB>CMO</SUB> is directly proportional to the host spheroid mass over 4 orders of magnitude. We therefore suggest that the dE,N nuclei may be the low-mass analogs of supermassive black holes and that these two types of CMOs may have both developed starting from similar initial formation processes. The overlap mass interval between the two types of CMOs is small and suggests that for M<SUB>CMO</SUB>&gt;10<SUP>7</SUP> M<SUB>solar</SUB>, the formation of a black hole was strongly favored, perhaps because the initial gas infall to the center was too rapid and violent for star formation to occur efficiently.

[]

https://arxiv.org/pdf/astro-ph/0603801.pdf

2019NewAR..8501524I

A review of quasi-periodic oscillations from black hole X-ray binaries: Observation and theory

2019-01-01

['black hole physics', 'neutron', 'accretion disks', '-', '-']

[]

Black hole and neutron star X-ray binary systems routinely show quasi-periodic oscillations (QPOs) in their X-ray flux. Despite being strong, easily measurable signals, their physical origin has long remained elusive. However, recent observational and theoretical work has greatly improved our understanding. Here, we briefly review the basic phenomenology of the different varieties of QPO in both black hole and neutron star systems before focusing mainly on low frequency QPOs in black hole systems, for which much of the recent progress has been made. We describe the detailed statistical properties of these QPOs and review the physical models proposed in the literature, with particular attention to those based on Lense-Thirring precession. This is a relativistic effect whereby a spinning massive object twists up the surrounding spacetime, inducing nodal precession in inclined orbits. We review the theory describing how an accretion flow reacts to the Lense-Thirring effect, including analytic theory and recent numerical simulations. We then describe recent observational tests that provide very strong evidence that at least a certain type of low frequency QPOs are a geometric effect, and good evidence that they are the result of precession. We discuss the possibility of the spin axis of the compact object being misaligned with the binary rotation axis for a large fraction of X-ray binaries, as is required for QPOs to be driven specifically by Lense-Thirring precession, as well as some outstanding gaps in our understanding and future opportunities provided by X-ray polarimeters and/or high throughput X-ray detectors.

[]

https://arxiv.org/pdf/2001.08758.pdf

2010JHEP...04..082C

Black holes in gravity with conformal anomaly and logarithmic term in black hole entropy

2010-01-01

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

[]

We present a class of exact analytic and static, spherically symmetric black hole solutions in the semi-classical Einstein equations with Weyl anomaly. The solutions have two branches, one is asymptotically flat and the other asymptotically de Sitter. We study thermodynamic properties of the black hole solutions and find that there exists a logarithmic correction to the well-known Bekenstein-Hawking area entropy. The logarithmic term might come from non-local terms in the effective action of gravity theories. The appearance of the logarithmic term in the gravity side is quite important in the sense that with this term one is able to compare black hole entropy up to the subleading order, in the gravity side and in the microscopic statistical interpretation side.

[]

https://arxiv.org/pdf/0911.4379.pdf

2015ApJ...812...72A

The Coevolution of Nuclear Star Clusters, Massive Black Holes, and Their Host Galaxies

2015-01-01

['galaxies evolution', 'galaxies formation', 'galaxies nuclei', 'galaxy center', 'galaxies quasars', '-', '-', '-']

[]

Studying how nuclear star clusters (NSCs) form and how they are related to the growth of the central massive black holes (MBHs) and their host galaxies is fundamental for our understanding of the evolution of galaxies and the processes that have shaped their central structures. We present the results of a semi-analytical galaxy formation model that follows the evolution of dark matter halos along merger trees, as well as that of the baryonic components. This model allows us to study the evolution of NSCs in a cosmological context, by taking into account the growth of NSCs due to both dynamical-friction-driven migration of stellar clusters and star formation triggered by infalling gas, while also accounting for dynamical heating from (binary) MBHs. We find that in situ star formation contributes a significant fraction (up to ∼80%) of the total mass of NSCs in our model. Both NSC growth through in situ star formation and that through star cluster migration are found to generate NSC—host galaxy scaling correlations that are shallower than the same correlations for MBHs. We explore the role of galaxy mergers on the evolution of NSCs and show that observational data on NSC—host galaxy scaling relations provide evidence of partial erosion of NSCs by MBH binaries in luminous galaxies. We show that this observational feature is reproduced by our models, and we make predictions about the NSC and MBH occupation fraction in galaxies. We conclude by discussing several implications for theories of NSC formation.

[]

https://arxiv.org/pdf/1506.02050.pdf

2004NewAR..48..993K

Strong-field tests of gravity using pulsars and black holes

2004-01-01

['astrophysics', '-']

[]

The sensitivity of the SKA enables a number of tests of theories of gravity. A Galactic Census of pulsars will discover most of the active pulsars in the Galaxy beamed toward us. In this census will almost certainly be pulsar-black hole binaries as well as pulsars orbiting the super-massive black hole in the Galactic centre. These systems are unique in their capability to probe the ultra-strong field limit of relativistic gravity. These measurements can be used to test the Cosmic Censorship Conjecture and the No-Hair theorem. The large number of millisecond pulsars discovered with the SKA will also provide a dense array of precision clocks on the sky. These clocks will act as the multiple arms of a huge gravitational wave detector, which can be used to detect and measure the stochastic cosmological gravitational wave background that is expected from a number of sources.

[]

https://arxiv.org/pdf/astro-ph/0409379.pdf

2005CQGra..22.5121G

Phase transitions near black hole horizons

2005-01-01

['-']

[]

The Reissner Nordström black hole in four dimensions can be made unstable without violating the dominant energy condition by introducing a real massive scalar with non-renormalizable interactions with the gauge field. New stable black hole solutions then exist with greater entropy for fixed mass and charge than the Reissner Nordström solution. In these new solutions, the scalar condenses to a non-zero value near the horizon. Various generalizations of these hairy black holes are discussed, and an attempt is made to characterize when black hole hair can occur.

[]

https://arxiv.org/pdf/hep-th/0505189.pdf

2005JHEP...10..096D

Precision counting of small black holes

2005-01-01

['-']

[]

It has recently been proposed that a class of supersymmetric higher-derivative interactions in Script N = 2 supergravity may encapsulate an infinite number of finite size corrections to the microscopic entropy of certain supersymmetric black holes. If this proposal is correct, it allows one to probe the string theory description of black-hole micro-states to far greater accuracy than has been possible before. We test this proposal for ``small'' black holes whose microscopic degeneracies can be computed exactly by counting the corresponding perturbative BPS states. We also study the ``black hole partition sum'' using general properties of of BPS degeneracies. This complements and extends our earlier work in [1].

[]

https://arxiv.org/pdf/hep-th/0507014.pdf

2015MNRAS.447.2123C

Growth and activity of black holes in galaxy mergers with varying mass ratios

2015-01-01

['galaxies active', 'galaxies interactions', 'galaxies nuclei', '-']

[]

We study supermassive black holes (BHs) in merging galaxies, using a suite of hydrodynamical simulations with very high spatial (∼10 pc) and temporal (∼1 Myr) resolution, where we vary the initial mass ratio, the orbital configuration, and the gas fraction. (i) We address the question of when and why, during a merger, increased BH accretion occurs, quantifying gas inflows and BH accretion rates. (ii) We also quantify the relative effectiveness in inducing active galactic nuclei activity of merger-related versus secular-related causes, by studying different stages of the encounter: the stochastic (or early) stage, the (proper) merger stage, and the remnant (or late) stage. (iii) We assess which galaxy mergers preferentially enhance BH accretion, finding that the initial mass ratio is the most important factor. (iv) We study the evolution of the BH masses, finding that the BH mass contrast tends to decrease in minor mergers and to increase in major mergers. This effect hints at the existence of a preferential range of mass ratios for BHs in the final pairing stages. (v) In both merging and dynamically quiescent galaxies, the gas accreted by the BH is not necessarily the gas with low angular momentum, but the gas that loses angular momentum.

[]

https://arxiv.org/pdf/1409.0004.pdf

2014MPLA...2940005B

Signatures of primordial black hole dark matter

2014-01-01

['elementary particles', 'cosmology early universe', '-', 'cosmology dark matter', '-', '-', '-', '-', '-', '-']

[]

The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro-world and mechanisms of its symmetry breaking. In the early Universe heavy metastable particles can dominate, leaving primordial black holes (PBHs) after their decay, as well as the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which massive black holes (BHs) and/or their clusters can originate. PBHs can be formed in such transitions within a narrow interval of masses about 10<SUP>17</SUP>g and, avoiding severe observational constraints on PBHs, can be a candidate for the dominant form of dark matter. PBHs in this range of mass can give solution of the problem of reionization in the Universe at the redshift z 5-10. Clusters of massive PBHs can serve as a nonlinear seeds for galaxy formation, while PBHs evaporating in such clusters can provide an interesting interpretation for the observations of point-like gamma-ray sources. Analysis of possible PBH signatures represents a universal probe for super-high energy physics in the early Universe in studies of indirect effects of the dark matter.

[]

https://arxiv.org/pdf/1410.0203.pdf

2017JCAP...10..046P

Quantum diffusion during inflation and primordial black holes

2017-01-01

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

[]

We calculate the full probability density function (PDF) of inflationary curvature perturbations, even in the presence of large quantum backreaction. Making use of the stochastic-δ N formalism, two complementary methods are developed, one based on solving an ordinary differential equation for the characteristic function of the PDF, and the other based on solving a heat equation for the PDF directly. In the classical limit where quantum diffusion is small, we develop an expansion scheme that not only recovers the standard Gaussian PDF at leading order, but also allows us to calculate the first non-Gaussian corrections to the usual result. In the opposite limit where quantum diffusion is large, we find that the PDF is given by an elliptic theta function, which is fully characterised by the ratio between the squared width and height (in Planck mass units) of the region where stochastic effects dominate. We then apply these results to the calculation of the mass fraction of primordial black holes from inflation, and show that no more than ~ 1 e-fold can be spent in regions of the potential dominated by quantum diffusion. We explain how this requirement constrains inflationary potentials with two examples.

[]

https://arxiv.org/pdf/1707.00537.pdf

2015ApJ...806L..14P

Relativistic Simulations of Black Hole-Neutron Star Coalescence: The Jet Emerges

2015-01-01

['black hole physics', 'gamma rays', 'gravitation', 'gravitational waves', '-', '-', '-']

[]

We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of a binary black hole-neutron star (BHNS) on a quasicircular orbit that undergoes merger. The binary mass ratio is 3:1, the black hole initial spin parameter a/m=0.75 (m is the black hole Christodoulou mass) aligned with the orbital angular momentum, and the neutron star is an irrotational {Γ }=2 polytrope. About two orbits prior to merger (at time t={{t}<SUB>B</SUB>}), we seed the neutron star with a dynamically weak interior dipole magnetic field that extends into the stellar exterior. At t={{t}<SUB>B</SUB>}, the exterior has a low-density atmosphere with a constant plasma parameter β \equiv {{P}<SUB>gas</SUB>}/{{P}<SUB>mag</SUB>}. Varying β at t<SUB>B</SUB> in the exterior from 0.1 to 0.01, we find that at a time ∼ 4000M∼ 100({{M}<SUB>NS</SUB>}/1.4{{M}<SUB>⊙ </SUB>}) ms (M is the total (ADM) mass) following the onset of accretion of tidally disrupted debris, magnetic winding above the remnant black hole poles builds up the magnetic field sufficiently to launch a mildly relativistic, collimated outflow—an incipient jet. The duration of the accretion and the lifetime of the jet is {Δ }t∼ 0.5({{M}<SUB>NS</SUB>}/1.4{{M}<SUB>⊙ </SUB>}) s. Our simulations furnish the first explicit examples in GRMHD that show that a jet can emerge following a BHNS merger.

[]

https://arxiv.org/pdf/1410.7392.pdf

2020EPJC...80..872Z

Shadows and photon spheres with spherical accretions in the four-dimensional Gauss-Bonnet black hole

2020-01-01

['-', '-']

[]

We investigate the shadows and photon spheres of the four-dimensional Gauss-Bonnet black hole with the static and infalling spherical accretions. We show that, for both cases, there always exist shadows and photon spheres. The radii of the shadows and photon spheres are independent of the profiles of accretion for a fixed Gauss-Bonnet constant, implying that the shadow is a signature of the spacetime geometry and it is hardly influenced by accretion. Because of the Doppler effect, the shadows of the infalling accretion are found to be darker than in the static case. We also investigate the effect of the Gauss-Bonnet constant on the shadow and photon spheres, and we find that the larger the Gauss-Bonnet constant is, the smaller the radii of the shadow and photon spheres will be. In particular, the observed specific intensity increases as the Gauss-Bonnet constant grows.

[]

https://arxiv.org/pdf/2004.12074.pdf

2017PhRvD..96b4058B

Numerical relativity waveform surrogate model for generically precessing binary black hole mergers

2017-01-01

['-']

[]

A generic, noneccentric binary black hole (BBH) system emits gravitational waves (GWs) that are completely described by seven intrinsic parameters: the black hole spin vectors and the ratio of their masses. Simulating a BBH coalescence by solving Einstein's equations numerically is computationally expensive, requiring days to months of computing resources for a single set of parameter values. Since theoretical predictions of the GWs are often needed for many different source parameters, a fast and accurate model is essential. We present the first surrogate model for GWs from the coalescence of BBHs including all seven dimensions of the intrinsic noneccentric parameter space. The surrogate model, which we call NRSur7dq2, is built from the results of 744 numerical relativity simulations. NRSur7dq2 covers spin magnitudes up to 0.8 and mass ratios up to 2, includes all ℓ≤4 modes, begins about 20 orbits before merger, and can be evaluated in ∼50 ms . We find the largest NRSur7dq2 errors to be comparable to the largest errors in the numerical relativity simulations, and more than an order of magnitude smaller than the errors of other waveform models. Our model, and more broadly the methods developed here, will enable studies that were not previously possible when using highly accurate waveforms, such as parameter inference and tests of general relativity with GW observations.

[]

https://arxiv.org/pdf/1705.07089.pdf

2009PhRvL.102s1301E

World-Volume Effective Theory for Higher-Dimensional Black Holes

2009-01-01

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

[]

We argue that the main feature behind novel properties of higher-dimensional black holes, compared to four-dimensional ones, is that their horizons can have two characteristic lengths of very different size. We develop a long-distance world-volume effective theory that captures the black hole dynamics at scales much larger than the short scale. In this limit the black hole is regarded as a blackfold: a black brane (possibly boosted locally) whose world volume spans a curved submanifold of the spacetime. This approach reveals black objects with novel horizon geometries and topologies more complex than the black ring, but more generally it provides a new organizing framework for the dynamics of higher-dimensional black holes.

[]

https://arxiv.org/pdf/0902.0427.pdf

2007JHEP...10..110E

The phase structure of higher-dimensional black rings and black holes

2007-01-01

['-']

[]

We construct an approximate solution for an asymptotically flat, neutral, thin rotating black ring in any dimension D &gt;= 5 by matching the near-horizon solution for a bent boosted black string, to a linearized gravity solution away from the horizon. The rotating black ring solution has a regular horizon of topology S<SUP>1</SUP> × S<SUP>D-3</SUP> and incorporates the balancing condition of the ring as a zero-tension condition. For D = 5 our method reproduces the thin ring limit of the exact black ring solution. For D &gt;= 6 we show that the black ring has a higher entropy than the Myers-Perry black hole in the ultra-spinning regime. By exploiting the correspondence between ultra-spinning black holes and black membranes on a two-torus, we take steps towards qualitatively completing the phase diagram of rotating blackfolds with a single angular momentum. We are led to propose a connection between MP black holes and black rings, and between MP black holes and black Saturns, through merger transitions involving two kinds of `pinched' black holes. More generally, the analogy suggests an infinite number of pinched black holes of spherical topology leading to a complicated pattern of connections and mergers between phases.

[]

https://arxiv.org/pdf/0708.2181.pdf

1997gr.qc....10076B

Quantum Black Holes as Atoms

1997-01-01

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

[]

In some respects the black hole plays the same role in gravitation that the atom played in the nascent quantum mechanics. This analogy suggests that black hole mass $M$ might have a discrete spectrum. I review the physical arguments for the expectation that black hole horizon area eigenvalues are uniformly spaced, or equivalently, that the spacing between stationary black hole mass levels behaves like 1/M. This sort of spectrum has also emerged in a variety of formal approaches to black hole quantization by a number of workers (with some notable exceptions). If true, this result indicates a distortion of the semiclassical Hawking spectrum which could be observable even for macroscopic black holes. Black hole entropy suggests that the mentioned mass levels should be degenerate to the tune of an exponential in $M^2$, as first noted by Mukhanov. This has implications for the statistics of the radiation. I also discuss open questions: whether radiative decay will spread the levels beyond recognition, whether extremal black holes can be described by this scheme, etc. I then describe an elementary algebra for the relevant black hole observables, an outcome of work by Mukhanov and myself, which reproduces the uniformly spaced area spectrum.

[]

https://arxiv.org/pdf/gr-qc/9710076.pdf

2009PhRvL.103w9001B

Comment on ``Kerr Black Holes as Particle Accelerators to Arbitrarily High Energy''

2009-01-01

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

[]

A Comment on the Letter by Máximo Bañados, Joseph Silk, and Stephen M. West [Phys. Rev. Lett.PRLTAO0031-9007 103, 111102 (2009)10.1103/PhysRevLett.103.111102].

[]

https://arxiv.org/pdf/0911.2243.pdf

2006ApJ...650...42L

Quasar Luminosity Functions from Joint Evolution of Black Holes and Host Galaxies

2006-01-01

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

[]

We show that our previously proposed antihierarchical baryon collapse scenario for the joint evolution of black holes and host galaxies predicts quasar luminosity functions at redshifts 1.5&lt;~z&lt;~6 and local properties in nice agreement with observations. In our model the quasar activity marks and originates the transition between an earlier phase of violent and heavily dust-enshrouded starburst activity promoting rapid black hole growth, and a later phase of almost passive evolution; the former is traced by the submillimeter-selected sources, while the latter accounts for the high number density of massive galaxies at substantial redshifts z&gt;~1.5, the population of extremely red objects, and the properties of local elliptical galaxies.

[]

https://arxiv.org/pdf/astro-ph/0603819.pdf

2023PhRvL.131t1401F

Recent Gravitational Wave Observation by Pulsar Timing Arrays and Primordial Black Holes: The Importance of Non-Gaussianities

2023-01-01

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

[]

We study whether the signal seen by pulsar timing arrays (PTAs) may originate from gravitational waves (GWs) induced by large primordial perturbations. Such perturbations may be accompanied by a sizable primordial black hole (PBH) abundance. We improve existing analyses and show that PBH overproduction disfavors Gaussian scenarios for scalar-induced GWs at 2 σ and single-field inflationary scenarios, accounting for non-Gaussianity, at 3 σ as the explanation of the most constraining NANOGrav 15-year data. This tension can be relaxed in models where non-Gaussianities suppress the PBH abundance. On the flip side, the PTA data does not constrain the abundance of PBHs.

[]

https://arxiv.org/pdf/2306.17149.pdf

2016Natur.533..504C

Suppressing star formation in quiescent galaxies with supermassive black hole winds

2016-01-01

['-']

[]

Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10<SUP>10</SUP> times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 10<SUP>10</SUP> times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

[]

https://arxiv.org/pdf/1605.07626.pdf

2020PhRvD.101d3015V

Lower bound on the primordial black hole merger rate

2020-01-01

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

[]

We derive a lower bound on the merger rate of primordial black hole (PBH) binaries by estimating the maximal fraction of binaries that were perturbed between formation in the early Universe and merger, and computing a conservative merger rate of perturbed binaries. This implies robust constraints on the PBH abundance in the range 1 - 100 M<SUB>⊙</SUB> . We further show that LIGO/Virgo design sensitivity has the potential to reach the PBH mass range of 1 0<SUP>-2</SUP>- 1 0<SUP>3</SUP>M<SUB>⊙</SUB> . The constraint from the merger rate of perturbed binaries is stronger if PBHs are initially spatially clustered.

[]

https://arxiv.org/pdf/1908.09752.pdf

2012NatCo...3.1304G

Low-mass black holes as the remnants of primordial black hole formation

2012-01-01

['-']

[]

Bridging the gap between the approximately ten solar mass `stellar mass' black holes and the `supermassive' black holes of millions to billions of solar masses are the elusive `intermediate-mass' black holes. Their discovery is key to understanding whether supermassive black holes can grow from stellar-mass black holes or whether a more exotic process accelerated their growth soon after the Big Bang. Currently, tentative evidence suggests that the progenitors of supermassive black holes were formed as ~10<SUP>4</SUP>-10<SUP>5</SUP>M<SUB>solar</SUB> black holes via the direct collapse of gas. Ongoing searches for intermediate-mass black holes at galaxy centres will help shed light on this formation mechanism.

[]

https://arxiv.org/pdf/1211.7082.pdf

2012PhRvD..85l4056G

Bayesian model selection for testing the no-hair theorem with black hole ringdowns

2012-01-01

['-', '-', '-', '-', 'waves', '-', 'perturbation theory', '-', '-', '-', 'stars luminosity function;mass function', '-', '-', '-']

[]

In this paper we examine the extent to which black hole quasinormal modes (QNMs) could be used to test the no-hair theorem with future ground- and space-based gravitational-wave detectors. We model departures from general relativity (GR) by introducing extra parameters which change the mode frequencies or decay times from their values in GR. With the aid of Bayesian model selection, we assess the extent to which the presence of such a parameter could be inferred, and its value estimated. We find that it is harder to measure the departure of the mode decay times from their GR values than it is with the mode frequencies. The Einstein Telescope (ET, a third generation ground-based detector) could detect departures of as little as 8% in the frequency of the dominant QNM mode of a 500M<SUB>⊙</SUB> black hole, out to a maximum range of ≃6Gpc (z≃0.91). The New Gravitational Observatory (NGO, an ESA space mission to detect gravitational waves) can detect departures of ∼0.6% in a 10<SUP>8</SUP>M<SUB>⊙</SUB> black hole to a luminosity distance of 50 Gpc (z≃5.1), and departures of ∼10% in a 10<SUP>6</SUP>M<SUB>⊙</SUB> black hole to a luminosity distance of ≃6Gpc. In this exploratory work we have made a specific choice of source position (overhead), orientation (inclination angle of π/3) and mass ratio of progenitor binary (m<SUB>1</SUB>/m<SUB>2</SUB>=2). A more exhaustive Monte Carlo simulation that incorporates progenitor black hole spins and a hierarchical model for the growth of massive black holes is needed to evaluate a more realistic picture of the possibility of ET and NGO to carry out such tests.

[]

https://arxiv.org/pdf/1111.5819.pdf

2006PhRvD..74h4021K

Gravitational perturbations of higher dimensional rotating black holes: Tensor perturbations

2006-01-01

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

[]

Assessing the stability of higher-dimensional rotating black holes requires a study of linearized gravitational perturbations around such backgrounds. We study perturbations of Myers-Perry black holes with equal angular momenta in an odd number of dimensions (greater than five), allowing for a cosmological constant. We find a class of perturbations for which the equations of motion reduce to a single radial equation. In the asymptotically flat case, we find no evidence of any instability. In the asymptotically anti-de Sitter case, we demonstrate the existence of a superradiant instability that sets in precisely when the angular velocity of the black hole exceeds the speed of light from the point of view of the conformal boundary. We suggest that the end point of the instability may be a stationary, nonaxisymmetric black hole.

[]

https://arxiv.org/pdf/hep-th/0606076.pdf

2020PhLB..80535468F

Charged black holes in AdS spaces in 4D Einstein Gauss-Bonnet gravity

2020-01-01

['-', '-']

[]

Recently a non-trivial 4-dimensional theory of gravity that claims to circumvent Lovelock's theorem and avoid Ostrogradsky instability was formulated in Glavan and Lin (2020) [1]. This theory, named "4D Einstein Gauss-Bonnet gravity", presents several novel predictions for cosmology and black hole physics. In this paper, we generalize the vacuum black hole solution of Glavan &amp; Lin to include electric charge in an anti-de Sitter space and explore some properties of this solution such as the asymptotics, properties of the horizons, the general relativity limit and thermodynamics.

[]

https://arxiv.org/pdf/2003.05491.pdf

2014Natur.505..378C

A Be-type star with a black-hole companion

2014-01-01

['-', '-']

[]

Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the approximately 80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC656 (ref. 5; also known as HD215227), although that conclusion was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of MWC656. This, together with an improved radial velocity curve of the Be star through fitting sharp FeII profiles from the equatorial disk, and a refined Be classification (to that of a B1.5-B2 III star), indicates that a black hole of 3.8 to 6.9 solar masses orbits MWC656, the candidate counterpart of the γ-ray source AGLJ2241+4454 (refs 5, 6). The black hole is X-ray quiescent and fed by a radiatively inefficient accretion flow giving a luminosity less than 1.6×10<SUP>-7</SUP> times the Eddington luminosity. This implies that Be binaries with black-hole companions are difficult to detect in conventional X-ray surveys.

[]

https://arxiv.org/pdf/1401.3711.pdf

2014Sci...345.1330A

Rapid growth of seed black holes in the early universe by supra-exponential accretion

2014-01-01

['-', '-']

[]

Mass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation's push balances gravity's pull. However, even exponential growth at the Eddington-limited e-folding time t<SUB>E</SUB> ~ few × 0.01 billion years is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 billion years old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is bound in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretion radiation, while the low-mass BH's random motions suppress the formation of a slowly draining accretion disk. Supra-exponential growth can thus explain the puzzling emergence of supermassive BHs that power luminous quasars so soon after the Big Bang.

[]

https://arxiv.org/pdf/1408.1718.pdf

1993PhRvD..48..728J

Black hole radiation in the presence of a short distance cutoff

1993-01-01

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

[]

A derivation of the Hawking effect is given which avoids reference to field modes above some cutoff frequency ω<SUB>c</SUB>&gt;&gt;M<SUP>-1</SUP> in the free-fall frame of the black hole. To avoid reference to arbitrarily high frequencies, it is necessary to impose a boundary condition on the quantum field in a timelike region near the horizon, rather than on a (spacelike) Cauchy surface either outside the horizon or at early times before the horizon forms. Because of the nature of the horizon as an infinite redshift surface, the correct boundary condition at late times outside the horizon cannot be deduced, within the confines of a theory that applies only below the cutoff, from initial conditions prior to the formation of the hole. A boundary condition is formulated which leads to the Hawking effect in a cutoff theory. It is argued that it is possible the boundary condition is not satisfied, so that the spectrum of black hole radiation may be significantly different from that predicted by Hawking, even without the back reaction near the horizon becoming of order unity relative to the curvature.

[]

https://arxiv.org/pdf/hep-th/9303103.pdf

2004ApJ...602...66V

Difficulties with Recovering the Masses of Supermassive Black Holes from Stellar Kinematical Data

2004-01-01

['galaxies elliptical lenticular;cd', 'cd', 'galaxies nuclei', 'galaxies structure', 'stars kinematics and dynamics', 'astrophysics']

[]

We investigate the ability of three-integral, axisymmetric, orbit-based modeling algorithms to recover the parameters defining the gravitational potential (mass-to-light ratio Υ and black hole mass M<SUB>•</SUB>) in spheroidal stellar systems using stellar kinematical data. We show that the potential estimation problem is generically underdetermined when applied to long-slit kinematical data of the kind used for most black hole mass determinations to date. A range of parameters (Υ, M<SUB>•</SUB>) can provide equally good fits to the data, making it impossible to assign best-fit values. The indeterminacy arises from the large variety of orbital solutions that are consistent with a given mass model. We demonstrate the indeterminacy using a variety of data sets derived from realistic models, as well as published observations of the galaxy M32. The indeterminacy becomes apparent only when a sufficiently large number of distinct orbits are supplied to the modeling algorithm; if too few orbits are used, spurious minima appear in the χ<SUP>2</SUP>(Υ,M<SUB>•</SUB>) contours, and these minima do not necessarily coincide with the parameters defining the gravitational potential. We show that the range of degeneracy in M<SUB>•</SUB> depends on the degree to which the data resolve the radius of influence r<SUB>h</SUB> of the black hole. For FWHM/2r<SUB>h</SUB>&gt;~0.5, where FWHM refers to the instrumental resolution, we find that only very weak constraints can be placed on M<SUB>•</SUB>. In the case of M32, our reanalysis demonstrates that when a large orbit library is used, data published prior to 2000 (FWHM/2r<SUB>h</SUB>~0.25) are equally consistent with black hole masses in the range 1.5×10<SUP>6</SUP>M<SUB>solar</SUB>&lt;M<SUB>•</SUB>&lt;5×10<SUP>6</SUP> M<SUB>solar</SUB>, with no preferred value in that range. Exactly the same data can reproduce previous published results with smaller orbit libraries. While the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) data for this galaxy (FWHM/2r<SUB>h</SUB>~0.06) may overcome the degeneracy in M<SUB>•</SUB>, HST data for most galaxies do not resolve the black hole's sphere of influence and in these galaxies the degree of degeneracy allowed by the data may be greater than previously believed. We investigate the effect of regularization, or smoothness constraints, on the degree of degeneracy of the solutions. Enforcing smoothness reduces the range of acceptable models, but we find no indication that the true potential can be recovered simply by enforcing smoothing. For a given smoothing level, all solutions in the minimum χ<SUP>2</SUP> valley exhibit similar levels of noise; as the smoothing is increased, there is a systematic shift in the midpoint of the χ<SUP>2</SUP> valley, until at a high level of smoothing the solution is biased with respect to the true solution. These experiments suggest both that the indeterminacy is real (i.e., that it is not an artifact associated with nonsmooth solutions) and that there is no known empirical way to choose the smoothing parameter to ensure that the correct solution is selected.

[]

https://arxiv.org/pdf/astro-ph/0210379.pdf

2007MNRAS.379..711G

The black hole mass - spheroid luminosity relation

2007-01-01

['black hole physics', 'galaxies bulges', 'galaxies photometry', 'astrophysics']

[]

The differing M<SUB>bh</SUB> -L relations presented in McLure &amp; Dunlop, Marconi &amp; Hunt and Erwin et al. have been investigated. A number of issues have been identified and addressed in each of these studies, including but not limited to the removal of a dependency on the Hubble constant, a correction for dust attenuation in the bulges of disc galaxies, the identification of lenticular galaxies previously treated as elliptical galaxies and the application of the same (Y | X) regression analysis. These adjustments result in relations which now predict similar black hole masses. The optimal K-band relation is log(M<SUB>bh</SUB>/M<SUB>solar</SUB>) = -0.37(+/-0.04)(M<SUB>K</SUB> + 24) + 8.29(+/-0.08), with a total (not intrinsic) scatter in logM<SUB>bh</SUB> equal to 0.33dex. This level of scatter is similar to the value of 0.34dex from the relation of Tremaine et al. and compares favourably with the value of 0.31dex from the M<SUB>bh</SUB> -n relation of Graham &amp; Driver. Using different photometric data, consistent relations in the B and R band are also provided, although we do note that the small (N = 13) R-band sample used by Erwin et al. is found here to have a slope of -0.30 +/- 0.06. Performing a symmetrical regression on the larger K-band sample gives a slope of ~ -0.40, implying M<SUB>bh</SUB> ~ L<SUP>1.00</SUP>. Implications for galaxy-black hole co-evolution, in terms of dry mergers, are briefly discussed, as are the predictions for intermediate mass black holes. Finally, as noted by others, a potential bias in the galaxy sample used to define the M<SUB>bh</SUB> -L relations is shown and a corrective formula provided.

[]

https://arxiv.org/pdf/0705.0618.pdf

2010PhRvD..81l4021M

Gravitational signature of Schwarzschild black holes in dynamical Chern-Simons gravity

2010-01-01

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

[]

Dynamical Chern-Simons gravity is an extension of general relativity in which the gravitational field is coupled to a scalar field through a parity-violating Chern-Simons term. In this framework, we study perturbations of spherically symmetric black hole spacetimes, assuming that the background scalar field vanishes. Our results suggest that these spacetimes are stable, and small perturbations die away as a ringdown. However, in contrast to standard general relativity, the gravitational waveforms are also driven by the scalar field. Thus, the gravitational oscillation modes of black holes carry imprints of the coupling to the scalar field. This is a smoking gun for Chern-Simons theory and could be tested with gravitational-wave detectors, such as LIGO or LISA. For negative values of the coupling constant, ghosts are known to arise, and we explicitly verify their appearance numerically. Our results are validated using both time evolution and frequency domain methods.

[]

https://arxiv.org/pdf/1004.4007.pdf

2008ApJ...680.1359M

The Accretion Disk Wind in the Black Hole GRO J1655-40

2008-01-01

['accretion', 'accretion disks', '-', 'black hole physics', 'relativity', 'astrophysics']

[]

We report on simultaneous Chandra HETGS and RXTE observations of the transient stellar-mass black hole GRO J1655-40, made during its 2005 outburst. Chandra reveals a line-rich X-ray absorption spectrum consistent with a disk wind. Prior modeling of the spectrum suggested that the wind may be magnetically driven, potentially providing insights into the nature of disk accretion onto black holes. In this paper, we present results obtained with new models for this spectrum, generated using three independent photoionization codes: XSTAR, Cloudy, and our own code. Fits to the spectrum in particular narrow wavelength ranges, in evenly spaced wavelength slices, and across a broad wavelength band all strongly prefer a combination of high density, high ionization, and small inner radius. Indeed, the results obtained from all three codes require a wind that originates more than 10 times closer to the black hole and carrying a mass flux that is on the order of 1000 times higher than predicted by thermal driving models. If seminal work on thermally driven disk winds is robust, magnetic forces may play a role in driving the disk wind in GRO J1655-40. However, even these modeling efforts must be regarded as crude given the complexity of the spectra. We discuss these results in the context of accretion flows in black holes and other compact objects.

[]

https://arxiv.org/pdf/0802.2026.pdf

2019PhRvD..99f4035W

Black holes and binary mergers in scalar Gauss-Bonnet gravity: Scalar field dynamics

2019-01-01

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

[]

We study the nonlinear dynamics of black holes that carry scalar hair and binaries composed of such black holes. The scalar hair is due to a linear or exponential coupling between the scalar and the Gauss-Bonnet invariant. We work perturbatively in the coupling constant of that interaction but nonperturbatively in the fields. We first consider the dynamical formation of hair for isolated black holes of arbitrary spin and determine the final state. This also allows us to compute for the first time the scalar quasinormal modes of rotating black holes in the presence of this coupling. We then study the evolution of nonspinning black hole binaries with various mass ratios and produce the first scalar waveform for a coalescence. An estimate of the energy loss in scalar radiation and the effect this has on orbital dynamics and the phase of gravitational waves (GWs) (entering at quadratic order in the coupling) shows that GW detections can set the most stringent constraint to date on theories that exhibit a coupling between a scalar field and the Gauss-Bonnet invariant.

[]

https://arxiv.org/pdf/1810.05177.pdf

2013JCAP...08..052Y

Primordial black holes in non-Gaussian regimes

2013-01-01

['-']

[]

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution — which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f<SUB>NL</SUB>, g<SUB>NL</SUB>, etc.) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f<SUB>NL</SUB> or g<SUB>NL</SUB>, etc.) does not give accurate results.

[]

https://arxiv.org/pdf/1307.4995.pdf

2018JHEP...10..004C

Proof of the weak gravity conjecture from black hole entropy

2018-01-01

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

[]

We prove that higher-dimension operators contribute positively to the entropy of a thermodynamically stable black hole at fixed mass and charge. Our results apply whenever the dominant corrections originate at tree level from quantum field theoretic dynamics. More generally, positivity of the entropy shift is equivalent to a certain inequality relating the free energies of black holes. These entropy inequalities mandate new positivity bounds on the coefficients of higher-dimension operators. One of these conditions implies that the charge-to-mass ratio of an extremal black hole asymptotes to unity from above for increasing mass. Consequently, large extremal black holes are unstable to decay to smaller extremal black holes and the weak gravity conjecture is automatically satisfied. Our findings generalize to arbitrary spacetime dimension and to the case of multiple gauge fields. The assumptions of this proof are valid across a range of scenarios, including string theory constructions with a dilaton stabilized below the string scale.

[]

https://arxiv.org/pdf/1801.08546.pdf

2017arXiv171001722D

The interior of dynamical vacuum black holes I: The $C^0$-stability of the Kerr Cauchy horizon

2017-01-01

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

[]

We initiate a series of works where we study the interior of dynamical rotating vacuum black holes without symmetry. In the present paper, we take up the problem starting from appropriate Cauchy data for the Einstein vacuum equations defined on a hypersurface already within the black hole interior, representing the expected geometry just inside the event horizon. We prove that for all such data, the maximal Cauchy evolution can be extended across a non-trivial piece of Cauchy horizon as a Lorentzian manifold with continuous metric. In subsequent work, we will retrieve our assumptions on data assuming only that the black hole event horizon geometry suitably asymptotes to a rotating Kerr solution. In particular, if the exterior region of the Kerr family is proven to be dynamically stable---as is widely expected---then it will follow that the $C^0$-inextendibility formulation of Penrose's celebrated strong cosmic censorship conjecture is in fact false. The proof suggests, however, that the $C^0$-metric Cauchy horizons thus arising are generically singular in an essential way, representing so-called "weak null singularities", and thus that a revised version of strong cosmic censorship holds.

[]

https://arxiv.org/pdf/1710.01722.pdf

2016ApJ...832L..21A

Upper Limits on the Rates of Binary Neutron Star and Neutron Star-Black Hole Mergers from Advanced LIGO’s First Observing Run

2016-01-01

['stars binaries general', 'gamma rays', 'gravitational waves', 'stars black holes', '-', '-', '-', '-']

[]

We report here the non-detection of gravitational waves from the merger of binary-neutron star systems and neutron star-black hole systems during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). In particular, we searched for gravitational-wave signals from binary-neutron star systems with component masses \in [1,3] {M}<SUB>⊙ </SUB> and component dimensionless spins &lt;0.05. We also searched for neutron star-black hole systems with the same neutron star parameters, black hole mass \in [2,99] {M}<SUB>⊙ </SUB>, and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems and find that they could have detected the merger of binary-neutron star systems with component mass distributions of 1.35 ± 0.13 M <SUB>⊙</SUB> at a volume-weighted average distance of ∼70 Mpc, and for neutron star-black hole systems with neutron star masses of 1.4 M <SUB>⊙</SUB> and black hole masses of at least 5 M <SUB>⊙</SUB>, a volume-weighted average distance of at least ∼110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> for binary-neutron star systems and less than 3600 Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> for neutron star-black hole systems. We discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. However, we find that if no detection of neutron star-binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of {10}<SUB>-7</SUB><SUP>+20</SUP> Gpc<SUP>-3</SUP> yr<SUP>-1</SUP>, short gamma-ray bursts beamed toward the Earth, and assuming that all short gamma-ray bursts have binary-neutron star (neutron star-black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\buildrel{\circ}\over{.} {3}<SUB>-1.1</SUB><SUP>+1.7</SUP> (4\buildrel{\circ}\over{.} {3}<SUB>-1.9</SUB><SUP>+3.1</SUP>).

[]

https://arxiv.org/pdf/1607.07456.pdf

2016ApJ...825...52K

Models of Kilonova/Macronova Emission from Black Hole-Neutron Star Mergers

2016-01-01

['thermodynamics', 'gamma rays', 'gravitational waves', 'radiative transfer', 'stars black holes', '-', '-', '-']

[]

Black hole-neutron star (BH-NS) mergers are among the most promising gravitational-wave sources for ground-based detectors, and gravitational waves from BH-NS mergers are expected to be detected in the next few years. The simultaneous detection of electromagnetic counterparts with gravitational waves would provide rich information about merger events. Among the possible electromagnetic counterparts from BH-NS mergers is the so-called kilonova/macronova, emission powered by the decay of radioactive r-process nuclei, which is one of the best targets for follow-up observations. We derive fitting formulas for the mass and the velocity of ejecta from a generic BH-NS merger based on recently performed numerical-relativity simulations. We combine these fitting formulas with a new semi-analytic model for a BH-NS kilonova/macronova lightcurve, which reproduces the results of radiation-transfer simulations. Specifically, the semi-analytic model reproduces the results of each band magnitude obtained by the previous radiation-transfer simulations within ∼1 mag. By using this semi-analytic model we found that, at 400 Mpc, the kilonova/macronova is as bright as 22-24 mag for cases with a small chirp mass and a high black hole spin, and &gt;28 mag for a large chirp mass and a low black hole spin. We also apply our model to GRB 130603B as an illustration, and show that a BH-NS merger with a rapidly spinning black hole and a large neutron star radius is favored.

[]

https://arxiv.org/pdf/1601.07711.pdf

2019A&A...623A..79C

ALMA observations of molecular tori around massive black holes

2019-01-01

['galaxies active', 'galaxies intergalactic medium', 'galaxies kinematics and dynamics', 'galaxies nuclei', 'galaxies spiral', '-']

[]

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(3-2) emission in a sample of seven Seyfert/LINER galaxies at the unprecedented spatial resolution of 0<SUB>.</SUB><SUP>″</SUP>1 = 4-8 pc. Our aim is to explore the close environment of active galactic nuclei (AGN), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. The selected galaxies host low-luminosity AGN and have a wide range of activity types (Seyferts 1 to 2, LINERs), and barred or ringed morphologies. The observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. We call these structures molecular tori, even though they often appear as disks without holes in the center. They have varying orientations along the line of sight, unaligned with the host galaxy orientation. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 10<SUP>7</SUP> to 3.9 × 10<SUP>7</SUP> M<SUB>⊙</SUB>. The most edge-on orientations of the torus correspond to obscured Seyferts. In only one case (NGC 1365), the AGN is centered on the central gas hole of the torus. On a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. More frequently, the torus and the AGN are slightly off-centered with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10 pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge. In some cases, AGN feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article. <P />Based on observations carried out with ALMA in cycles 3 and 4.

[]

https://arxiv.org/pdf/1811.00984.pdf

2015Natur.526..542M

Flows of X-ray gas reveal the disruption of a star by a massive black hole

2015-01-01

['-']

[]

Tidal forces close to massive black holes can violently disrupt stars that make a close approach. These extreme events are discovered via bright X-ray and optical/ultraviolet flares in galactic centres. Prior studies based on modelling decaying flux trends have been able to estimate broad properties, such as the mass accretion rate. Here we report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 043234. Variability within the absorption-dominated spectra indicates that the gas is relatively close to the black hole. Narrow linewidths indicate that the gas does not stretch over a large range of radii, giving a low volume filling factor. Modest outflow speeds of a few hundred kilometres per second are observed; these are below the escape speed from the radius set by variability. The gas flow is consistent with a rotating wind from the inner, super-Eddington region of a nascent accretion disk, or with a filament of disrupted stellar gas near to the apocentre of an elliptical orbit. Flows of this sort are predicted by fundamental analytical theory and more recent numerical simulations.

[]

https://arxiv.org/pdf/1510.06348.pdf

2005MNRAS.363..353B

Imaging bright-spots in the accretion flow near the black hole horizon of Sgr A*

2005-01-01

['black hole physics', 'relativity', 'techniques interferometric', 'galaxy center', 'astronomy submillimeter', 'astrophysics']

[]

Images from the vicinity of the black hole horizon at the Galactic centre (Sgr A*) could be obtained in the near future with a Very Large Baseline Array of submillimetre telescopes. The recently observed short-term infrared and X-ray variability of the emission from Sgr A* implies that the accretion flow near the black hole is clumpy or unsteady. We calculate the appearance of a compact emission region (bright-spot) in a circular orbit around a spinning black hole as a function of orbital radius and orientation. We find that the mass and spin of the black hole can be extracted from their generic signatures on the spot image as well as on the light curves of its observed flux and polarization. The strong field distortion remains notable even when the spot image is smoothed over the expected ~20-μ as resolution of the future submillimetre observations.

[]

https://arxiv.org/pdf/astro-ph/0506433.pdf

1993NuPhB.394...73B

Liouville models of black hole evaporation

1993-01-01

['-']

[]

A renormalizable two-dimensional quantum field theory, containing a metric, a dilaton and N massless scalar matter fields, has been proposed as a model for black hole evaporation reflecting the conformal anomaly. Previous work on this model has been done in the large-N (weak coupling) approximation and clear evidence for Hawking radiation and its back-reaction on the metric has been seen. There are, however, quantum consistency questions since the original model was only designed to be a c = 26 conformal field theory in the weak coupling limit. In this paper we construct new theories, differing from the old only in the dilaton dependence of the cosmological constant and reducing to it in the weak coupling limit. They are exact c = 26 conformal field theories and presumably consistent frameworks for discussing this problem. We also study the new theories with a change in the Polyakov action proposed by Strominger with a view to eliminating unphysical ghost Hawking radiation. The classical equations of motion of the new theories are explicitly soluble, thus permitting an exact analysis of both static solutions and dynamic scenarios. While the static solutions are, by and large, physically reasonable, the dynamical solutions include puzzling examples where wrong-sign Hawking radiation is stimulated by allowing matter to fall into a static solution. We indicate how the latter problem may be resolved in the full quantum theory.

[]

https://arxiv.org/pdf/hep-th/9205089.pdf

1999PhRvD..59l4011C

Black hole lasers

1999-01-01

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

[]

High frequency dispersion does not alter the low frequency spectrum of Hawking radiation from a single black hole horizon, whether the dispersion entails subluminal or superluminal group velocities. We show here that in the presence of an inner horizon as well as an outer horizon the superluminal case differs dramatically however. The negative energy partners of Hawking quanta return to the outer horizon and stimulate more Hawking radiation if the field is bosonic or suppress it if the field is fermionic. This process leads to exponential growth or damping of the radiated flux and correlations among the quanta emitted at different times, unlike in the usual Hawking effect. These phenomena may be observable in condensed matter black hole analogues that exhibit ``superluminal'' dispersion.

[]

https://arxiv.org/pdf/hep-th/9806203.pdf

2002PhLB..533..302V

Semiclassical corrections to the Bekenstein-Hawking entropy of the BTZ black hole via self-gravitation

2002-01-01

['-', '-']

[]

Hawking radiation is viewed as a tunnelling process. In this way the effect of self-gravitation gives rise to semiclassical corrections to the entropy of the (2+1) BTZ black hole. The modified entropy, due to specific modelling of the self-gravitation effect, of the (2+1) BTZ black hole is evaluated. To first order in ω which is a shell of energy radiated outwards the event horizon of the BTZ black hole, modified entropy is proportional to the horizon. In this semiclassical analysis, corrections to the Bekenstein-Hawking formula S<SUB>BH</SUB>=A<SUB>H</SUB>/4l<SUB>P</SUB><SUP>2</SUP> are found to be negative and the proportionality factor connecting the modified entropy, S<SUB>bh</SUB>, of the (2+1) BTZ black hole to the Bekenstein-Hawking entropy, S<SUB>BH</SUB>, is evaluated to first order in ω.

[]

https://arxiv.org/pdf/hep-th/0109108.pdf

2009ApJ...706L.230M

The First Accurate Parallax Distance to a Black Hole

2009-01-01

['astrometry', 'astronomy radio', '-', '-', 'stars kinematics and dynamics', 'astronomy x rays', '-']

[]

Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 ± 0.024 mas, corresponding to a distance of 2.39 ± 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is &lt;1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.

[]

https://arxiv.org/pdf/0910.5253.pdf

2011JHEP...09..017T

Black holes and black branes in Lifshitz spacetimes

2011-01-01

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

[]

We construct analytic solutions describing black holes and black branes in asymptotically Lifshitz spacetimes with arbitrary dynamical exponent z and for arbitrary number of dimensions. The model considered consists of Einstein gravity with negative cosmological constant, a scalar, and N U(1) gauge fields with dilatonic-like couplings. We study the phase diagrams and thermodynamic instabilities of the solution, and find qualitative differences between the cases with 1 ≤ z &lt; 2, z = 2 and z &gt; 2.

[]

https://arxiv.org/pdf/1105.6335.pdf

2007MNRAS.374.1557J

The aftermath of the first stars: massive black holes

2007-01-01

['astrochemistry', 'stars fundamental parameters', 'ism hii regions', 'galaxies formation', 'cosmology theory', 'cosmology early universe', 'astrophysics']

[]

We investigate the evolution of the primordial gas surrounding the first massive black holes formed by the collapse of Population III stars at redshifts z &gt;~ 20. Carrying out three-dimensional hydrodynamical simulations using GADGET, we study the dynamical, thermal and chemical evolution of the first relic HII regions. We also carry out simulations of the mergers of relic HII regions with neighbouring neutral minihaloes, which contain high-density primordial gas that could accrete on to a Population III remnant black hole. We find that there may have been a significant time delay, of the order of ~10<SUP>8</SUP> yr, between black hole formation and the onset of efficient accretion. The build-up of supermassive black holes, believed to power the z &gt;~ 6 quasars observed in the Sloan Digital Sky Survey, therefore faces a crucial early bottleneck. More massive seed black holes may thus be required, such as those formed by the direct collapse of a primordial gas cloud facilitated by atomic line cooling. The high optical depth to Lyman-Werner (LW) photons that results from the high fraction of H<SUB>2</SUB> molecules that form in relic HII regions, combined with the continued formation of H<SUB>2</SUB> inside the dynamically expanding relic HII region, leads to shielding of the molecules inside these regions at least until a critical background LW flux of ~10<SUP>-24</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP> Hz<SUP>-1</SUP> sr<SUP>-1</SUP> is established. Furthermore, we find that a high fraction of deuterium hydride (HD) molecules, X<SUB>HD</SUB> &gt;~ 10<SUP>-7</SUP>, is formed, potentially enabling the formation of Population II.5 stars, with masses of the order of ~10M<SUB>solar</SUB>, during later stages of structure formation when the relic HII region gas is assembled into a sufficiently deep potential well to gravitationally confine the gas again.

[]

https://arxiv.org/pdf/astro-ph/0605691.pdf

2003ApJ...593L..77H

The Need for a Second Black Hole at the Galactic Center

2003-01-01

['black hole physics', 'galaxy center', 'galaxy kinematics and dynamics', 'galaxy nucleus', 'astrophysics']

[]

Deep infrared observations and long-term monitoring programs have provided dynamical evidence of a supermassive black hole of mass 3×10<SUP>6</SUP> M<SUB>solar</SUB> associated with the radio source Sagittarius A* at the center of our Galaxy. The brightest stars orbiting within 0.1 pc of the black hole appear to be young, massive main-sequence stars, in spite of an environment near the black hole that is hostile to star formation. We discuss mechanisms by which stars born outside the central parsec can sink toward the black hole and conclude that the drag coming from plausible stellar populations does not operate on the short timescales required by the stellar ages. We propose that these stars were dragged in by a second black hole of mass ~10<SUP>3</SUP>-10<SUP>4</SUP> M<SUB>solar</SUB>, which would be classified as an intermediate-mass black hole. We discuss the implications for the stellar populations and the kinematics in the Galactic center. Finally, we note that continued astrometric monitoring of the central radio source offers us the prospect for a direct detection of such objects.

[]

https://arxiv.org/pdf/astro-ph/0306074.pdf

2004JHEP...07..051H

Black Holes with Scalar Hair and Asymptotics in N = 8 Supergravity

2004-01-01

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

[]

We consider Script N = 8 gauged supergravity in D = 4 and D = 5. We show one can weaken the boundary conditions on the metric and on all scalars with m<SUP>2</SUP> &lt; - (D - 1)<SUP>2</SUP>/4 + 1 while preserving the asymptotic anti-de Sitter (AdS) symmetries. Each scalar admits a one-parameter family of AdS-invariant boundary conditions for which the metric falls off slower than usual. The generators of the asymptotic symmetries are finite, but generically acquire a contribution from the scalars. For a large class of boundary conditions we numerically find a one-parameter family of black holes with scalar hair. These solutions exist above a certain critical mass and are disconnected from the Schwarschild-AdS black hole, which is a solution for all boundary conditions. We show the Schwarschild-AdS black hole has larger entropy than a hairy black hole of the same mass. The hairy black holes lift to inhomogeneous black brane solutions in ten or eleven dimensions. We briefly discuss how generalized AdS-invariant boundary conditions can be incorporated in the AdS/CFT correspondence.

[]

https://arxiv.org/pdf/hep-th/0404261.pdf

2012ApJ...755..133S

Sagittarius A* Accretion Flow and Black Hole Parameters from General Relativistic Dynamical and Polarized Radiative Modeling

2012-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxy center', 'polarization', 'radiative transfer', 'relativity', '-']

[]

We obtain estimates of Sgr A* accretion flow and black hole parameters by fitting polarized submillimeter observations with spectra computed using three-dimensional general relativistic (GR) magnetohydrodynamical (MHD) (GRMHD) simulations. Observations are compiled from averages over many epochs from reports in 29 papers for estimating the mean fluxes F <SUB>ν</SUB>, linear polarization (LP) fractions, circular polarization (CP) fractions, and electric vector position angles. GRMHD simulations are computed with dimensionless spins a <SUB>*</SUB> = 0, 0.5, 0.7, 0.9, 0.98 over a 20, 000M time interval. We perform fully self-consistent GR polarized radiative transfer using our new code to explore the effects of spin a <SUB>*</SUB>, inclination angle θ, position angle (P.A.), accretion rate \dot{M}, and electron temperature T<SUB>e</SUB> (T<SUB>e</SUB> is reported for radius 6M). By fitting the mean submillimeter fluxes and LP/CP fractions, we obtain estimates for these model parameters and determine the physical effects that could produce polarization signatures. Our best-bet model has a <SUB>*</SUB> = 0.5, θ = 75°, P.A. = 115°, \dot{M}=4.6×10^{-8} M_⊙ {{yr}}^{-1}, and T<SUB>e</SUB> = 3.1 × 10<SUP>10</SUP> K at 6M. The submillimeter CP is mainly produced by Faraday conversion as modified by Faraday rotation, and the emission region size at 230 GHz is consistent with the very long baseline interferometry size of 37 μas. Across all spins, model parameters are in the ranges θ = 42°-75°, \dot{M}=(1.4{--}7.0)× 10^{-8} M_⊙ {{yr}}^{-1}, and T<SUB>e</SUB> = (3-4) × 10<SUP>10</SUP> K. Polarization is found both to help differentiate models and to introduce new observational constraints on the effects of the magnetic field that might not be fit by accretion models so far considered.

[]

https://arxiv.org/pdf/1007.4832.pdf

2016JHEP...09..100D

Extended symmetries at the black hole horizon

2016-01-01

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

[]

We prove that non-extremal black holes in four-dimensional general relativity exhibit an infinite-dimensional symmetry in their near horizon region. By prescribing a physically sensible set of boundary conditions at the horizon, we derive the algebra of asymptotic Killing vectors, which is shown to be infinite-dimensional and includes, in particular, two sets of supertranslations and two mutually commuting copies of the Witt algebra. We define the surface charges associated to the asymptotic diffeomorphisms that preserve the boundary conditions and discuss the subtleties of this definition, such as the integrability conditions and the correct definition of the Dirac brackets. When evaluated on the stationary solutions, the only non-vanishing charges are the zero-modes. One of them reproduces the Bekenstein-Hawking entropy of Kerr black holes. We also study the extremal limit, recovering the NHEK geometry. In this singular case, where the algebra of charges and the integrability conditions get modified, we find that the computation of the zero-modes correctly reproduces the black hole entropy. Furthermore, we analyze the case of three spacetime dimensions, in which the integrability conditions notably simplify and the field equations can be solved analytically to produce a family of exact solutions that realize the boundary conditions explicitly. We examine other features, such as the form of the algebra in the extremal limit and the relation to other works in the literature.

[]

https://arxiv.org/pdf/1607.05703.pdf

2005NJPh....7..199N

Black holes in astrophysics

2005-01-01

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

[]

This paper reviews the current status of black hole (BH) astrophysics, focusing on topics of interest to a physics audience. Astronomers have discovered dozens of compact objects with masses greater than 3M<SUB>odot</SUB>, the likely maximum mass of a neutron star. These objects are identified as BH candidates. Some of the candidates have masses ~5M<SUB>odot</SUB> 20M<SUB>odot</SUB> and are found in x-ray binaries, while the rest have masses ~10<SUP>6</SUP>M<SUB>odot</SUB> 10<SUP>9.5</SUP>M<SUB>odot</SUB> and are found in galactic nuclei. A variety of methods are being tried to estimate the spin parameters of the candidate BHs. There is strong circumstantial evidence that many of the objects have event horizons, so there is good reason to believe that the candidates are true BHs. Recent MHD simulations of magnetized plasma accreting on rotating BHs seem to hint that relativistic jets may be produced by a magnetic analogue of the Penrose process.

[]

https://arxiv.org/pdf/gr-qc/0506078.pdf

2017MNRAS.466..677G

Raining on black holes and massive galaxies: the top-down multiphase condensation model

2017-01-01

['black hole physics', 'hydrodynamics', 'turbulence', 'methods numerical', 'galaxies elliptical lenticular;cd', 'cd', 'astronomy x rays', '-', '-', '-', '-', '-']

[]

The plasma haloes filling massive galaxies, groups and clusters are shaped by active galactic nucleus (AGN) heating and subsonic turbulence (σ<SUB>v</SUB> ∼ 150 km s<SUP>-1</SUP>), as probed by Hitomi. Novel 3D high-resolution simulations show the soft X-ray, keV hot plasma cools rapidly via radiative emission at the high-density interface of the turbulent eddies, stimulating a top-down condensation cascade of warm 10<SUP>4</SUP> K filaments. The kpc-scale ionized (optical/ultraviolet) filaments form a skin enveloping the neutral filaments (optical/infrared/21 cm). The peaks of the warm filaments further condense into cold molecular clouds (&lt;50 K; radio) with total mass of several 10<SUP>7</SUP> M<SUB>⊙</SUB> and inheriting the turbulent kinematics. In the core, the clouds collide inelastically, mixing angular momentum and leading to Chaotic Cold Accretion (CCA). The black hole accretion rate (BHAR) can be modelled via quasi-spherical viscous accretion, dot{M}_bullet ∝ ν _c, with clump collisional viscosity ν<SUB>c</SUB> ≡ λ<SUB>c</SUB> σ<SUB>v</SUB> and λ<SUB>c</SUB> ∼ 100 pc. Beyond the core, pressure torques shape the angular momentum transport. In CCA, the BHAR is recurrently boosted up to 2 dex compared with the disc evolution, which arises as turbulence becomes subdominant. With negligible rotation too, compressional heating inhibits the molecular phase. The CCA BHAR distribution is lognormal with pink noise, f<SUP>-1</SUP> power spectrum characteristic of fractal phenomena. Such chaotic fluctuations can explain the rapid luminosity variability of AGN and high-mass X-ray binaries. An improved criterium to trace non-linear condensation is proposed: σ<SUB>v</SUB>/v<SUB>cool</SUB> ≲ 1. The three-phase CCA reproduces key observations of cospatial multiphase gas in massive galaxies, including Chandra X-ray images, SOAR Hα filaments and kinematics, Herschel [C<SUP>+</SUP>] emission and ALMA molecular associations. CCA plays important role in AGN feedback and unification, the evolution of BHs, galaxies and clusters.

[]

https://arxiv.org/pdf/1608.08216.pdf

2013ApJ...764...45K

The Demographics of Broad-line Quasars in the Mass-Luminosity Plane. II. Black Hole Mass and Eddington Ratio Functions

2013-01-01

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

[]

We employ a flexible Bayesian technique to estimate the black hole (BH) mass and Eddington ratio functions for Type 1 (i.e., broad line) quasars from a uniformly selected data set of ~58, 000 quasars from the Sloan Digital Sky Survey (SDSS) DR7. We find that the SDSS becomes significantly incomplete at M <SUB>BH</SUB> &lt;~ 3 × 10<SUP>8</SUP> M <SUB>⊙</SUB> or L/L <SUB>Edd</SUB> &lt;~ 0.07, and that the number densities of Type 1 quasars continue to increase down to these limits. Both the mass and Eddington ratio functions show evidence of downsizing, with the most massive and highest Eddington ratio BHs experiencing Type 1 quasar phases first, although the Eddington ratio number densities are flat at z &lt; 2. We estimate the maximum Eddington ratio of Type 1 quasars in the observable universe to be L/L <SUB>Edd</SUB> ~ 3. Consistent with our results in Shen &amp; Kelly, we do not find statistical evidence for a so-called sub-Eddington boundary in the mass-luminosity plane of broad-line quasars, and demonstrate that such an apparent boundary in the observed distribution can be caused by selection effect and errors in virial BH mass estimates. Based on the typical Eddington ratio in a given mass bin, we estimate growth times for the BHs in Type 1 quasars and find that they are comparable to or longer than the age of the universe, implying an earlier phase of accelerated (i.e., with higher Eddington ratios) and possibly obscured growth. The large masses probed by our sample imply that most of our BHs reside in what are locally early-type galaxies, and we interpret our results within the context of models of self-regulated BH growth.

[]

https://arxiv.org/pdf/1209.0477.pdf

2022Natur.603..237S

AGN as potential factories for eccentric black hole mergers

2022-01-01

['-', '-']

[]

There is some weak evidence that the black hole merger named GW190521 had a non-zero eccentricity<SUP>1,2</SUP>. In addition, the masses of the component black holes exceeded the limit predicted by stellar evolution<SUP>3</SUP>. The large masses can be explained by successive mergers<SUP>4,5</SUP>, which may be efficient in gas disks surrounding active galactic nuclei, but it is difficult to maintain an eccentric orbit all the way to the merger, as basic physics would argue for circularization<SUP>6</SUP>. Here we show that active galactic nuclei disk environments can lead to an excess of eccentric mergers, if the interactions between single and binary black holes are frequent<SUP>5</SUP> and occur with mutual inclinations of less than a few degrees. We further illustrate that this eccentric population has a different distribution of the inclination between the spin vectors of the black holes and their orbital angular momentum at merger<SUP>7</SUP>, referred to as the spin-orbit tilt, compared with the remaining circular mergers.

[]

https://arxiv.org/pdf/2010.09765.pdf

1998ApJ...506L..97N

The Alignment of Disk and Black Hole Spins in Active Galactic Nuclei

1998-01-01

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

[]

The inner parts of an accretion disk around a spinning black hole are forced to align with the spin of the hole by the Bardeen-Petterson effect. Assuming that any jet produced by such a system is aligned with the angular momentum of either the hole or the inner disk, this can, in principle, provide a mechanism for producing steady jets in active galactic nuclei (AGNs) whose direction is independent of the angular momentum of the accreted material. However, the torque that aligns the inner disk with the hole, also by Newton's third law, tends to align the spin of the hole with the outer accretion disk. In this Letter, we calculate this alignment timescale, t<SUB>align</SUB>, for a black hole powering an AGN, and we show that it is relatively short. This timescale is typically much less than the derived ages for jets in radio-loud AGNs and implies that the jet directions, in general, are not controlled by the spin of the black hole. We speculate that the jet directions are most likely controlled either by the angular momentum of the accreted material or by the gravitational potential of the host galaxy.

[]

https://arxiv.org/pdf/astro-ph/9808187.pdf

2007PhRvD..76j4018C

LISA detections of massive black hole inspirals: Parameter extraction errors due to inaccurate template waveforms

2007-01-01

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

[]

The planned Laser Interferometer Space Antenna (LISA) is expected to detect the inspiral and merger of massive black hole binaries (MBHBs) at z≲5 with signal-to-noise ratios (SNRs) of hundreds to thousands. Because of these high SNRs, and because these SNRs accrete over periods of weeks to months, it should be possible to extract the physical parameters of these systems with high accuracy; for instance, for a ∼10<SUP>6</SUP>M<SUB>⊙</SUB> MBHBs at z=1 it should be possible to determine the two masses to ∼0.1% and the sky location to ∼1°. However, those are just the errors due to noise: there will be additional “theoretical” errors due to inaccuracies in our best model waveforms, which are still only approximate. The goal of this paper is to estimate the typical magnitude of these theoretical errors. We develop mathematical tools for this purpose, and apply them to a somewhat simplified version of the MBHB problem, in which we consider just the inspiral part of the waveform and neglect spin-induced precession, eccentricity, and PN amplitude corrections. For this simplified version, we estimate that theoretical uncertainties in sky position will typically be ∼1°, i.e., comparable to the statistical uncertainty. For the mass and spin parameters, our results suggest that while theoretical errors will be rather small absolutely, they could still dominate over statistical errors (by roughly an order of magnitude) for the strongest sources. The tools developed here should be useful for estimating the magnitude of theoretical errors in many other problems in gravitational-wave astronomy.

[]

https://arxiv.org/pdf/0707.2982.pdf

2006PhR...422..119K

The phase transition between caged black holes and black strings

2006-01-01

['-', '-']

[]

Black-hole uniqueness is known to fail in higher dimensions, and the multiplicity of black hole phases leads to phase transitions physics in General Relativity. The black-hole black-string transition is a prime realization of such a system and its phase diagram has been the subject of considerable study in the last few years. The most surprising results seem to be the appearance of critical dimensions where the qualitative behavior of the system changes, and a novel kind of topology change. Recently, a full phase diagram was determined numerically, confirming earlier predictions for a merger of the black-hole and black-string phases and giving very strong evidence that the end-state of the Gregory-Laflamme instability is a black hole (in the dimension range 5⩽D⩽13). Here this progress is reviewed, illustrated with figures, put into a wider context, and the still open questions are listed.

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https://arxiv.org/pdf/hep-th/0411240.pdf

2016PhRvL.116x1104B

Theory-Agnostic Constraints on Black-Hole Dipole Radiation with Multiband Gravitational-Wave Astrophysics

2016-01-01

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

[]

The aLIGO detection of the black-hole binary GW150914 opens a new era for probing extreme gravity. Many gravity theories predict the emission of dipole gravitational radiation by binaries. This is excluded to high accuracy in binary pulsars, but entire classes of theories predict this effect predominantly (or only) in binaries involving black holes. Joint observations of GW150914-like systems by aLIGO and eLISA will improve bounds on dipole emission from black-hole binaries by 6 orders of magnitude relative to current constraints, provided that eLISA is not dramatically descoped.

[]

https://arxiv.org/pdf/1603.04075.pdf

2011PhLB..695..397M

Black holes in an ultraviolet complete quantum gravity

2011-01-01

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

[]

In this Letter we derive the gravity field equations by varying the action for an ultraviolet complete quantum gravity. Then we consider the case of a static source term and we determine an exact black hole solution. As a result we find a regular spacetime geometry: in place of the conventional curvature singularity extreme energy fluctuations of the gravitational field at small length scales provide an effective cosmological constant in a region locally described in terms of a de Sitter space. We show that the new metric coincides with the noncommutative geometry inspired Schwarzschild black hole. Indeed, we show that the ultraviolet complete quantum gravity, generated by ordinary matter is the dual theory of ordinary Einstein gravity coupled to a noncommutative smeared matter. In other words we obtain further insights about that quantum gravity mechanism which improves Einstein gravity in the vicinity of curvature singularities. This corroborates all the existing literature in the physics and phenomenology of noncommutative black holes.

[]

https://arxiv.org/pdf/1010.0680.pdf

2019Natur.566...85W

Formation of massive black holes in rapidly growing pre-galactic gas clouds

2019-01-01

['-']

[]

The origin of the supermassive black holes that inhabit the centres of massive galaxies remains unclear<SUP>1,2</SUP>. Direct-collapse black holes—remnants of supermassive stars, with masses around 10,000 times that of the Sun—are ideal seed candidates<SUP>3-6</SUP>. However, their very existence and their formation environment in the early Universe are still under debate, and their supposed rarity makes modelling their formation difficult<SUP>7,8</SUP>. Models have shown that rapid collapse of pre-galactic gas (with a mass infall rate above some critical value) in metal-free haloes is a requirement for the formation of a protostellar core that will then form a supermassive star<SUP>9,10</SUP>. Here we report a radiation hydrodynamics simulation of early galaxy formation<SUP>11,12</SUP> that produces metal-free haloes massive enough and with sufficiently high mass infall rates to form supermassive stars. We find that pre-galactic haloes and their associated gas clouds that are exposed to a Lyman-Werner intensity roughly three times the intensity of the background radiation and that undergo at least one period of rapid mass growth early in their evolution are ideal environments for the formation of supermassive stars. The rapid growth induces substantial dynamical heating<SUP>13,14</SUP>, amplifying the Lyman-Werner suppression that originates from a group of young galaxies 20 kiloparsecs away. Our results strongly indicate that the dynamics of structure formation, rather than a critical Lyman-Werner flux, is the main driver of the formation of massive black holes in the early Universe. We find that the seeds of massive black holes may be much more common than previously considered in overdense regions of the early Universe, with a co-moving number density up to 10<SUP>-3</SUP> per cubic megaparsec.

[]

https://arxiv.org/pdf/1901.07563.pdf

2017JPhCS.840a2032G

Massive Primordial Black Holes as Dark Matter and their detection with Gravitational Waves

2017-01-01

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

[]

Massive Primordial Black Holes (MPBH) can be formed after inflation due to broad peaks in the primordial curvature power spectrum that collapse gravitationally during the radiation era, to form clusters of black holes that merge and increase in mass after recombination, generating today a broad mass-spectrum of black holes with masses ranging from 0.01 to 10<SUP>5</SUP> M<SUB>⊙</SUB> . These MPBH could act as seeds for galaxies and quick-start structure formation, initiating reionization, forming galaxies at redshift z &gt; 10 and clusters at z &gt; 1. They may also be the seeds on which SMBH and IMBH form, by accreting gas onto them and forming the centers of galaxies and quasars at high redshift. They form at rest with zero spin and have negligible cross-section with ordinary matter. If there are enough of these MPBH, they could constitute the bulk of the Dark Matter today. Such PBH could be responsible for the observed fluctuations in the CIB and X-ray backgrounds. MPBH could be directly detected by the gravitational waves emitted when they merge to form more massive black holes, as recently reported by LIGO. Their continuous merging since recombination could have generated a stochastic background of gravitational waves that could eventually be detected by LISA and PTA. MPBH may actually be responsible for the unidentified point sources seen by Fermi, Magic and Chandra. Furthermore, the ejection of stars from shallow potential wells like those of Dwarf Spheroidals (DSph), via the gravitational slingshot effect, could be due to MPBH, thus alleviating the substructure and too-big-to-fail problems of standard collisionless CDM. Their mass distribution peaks at a few tens of M<SUB>⊙</SUB> today, and could therefore be detected also with long-duration microlensing events, as well as by the anomalous motion of stars in the field of GAIA. Their presence as CDM in the Universe could be seen in the time-dilation of strong-lensing images of quasars. The hierarchical large scale structure behaviour of MPBH does not differ from that of ordinary CDM.

[]

https://arxiv.org/pdf/1702.08275.pdf

2010MNRAS.402..673B

Evolution of supermassive stars as a pathway to black hole formation

2010-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxies nuclei', 'galaxies quasars', '-', '-']

[]

Supermassive stars, with masses &gt;~10<SUP>6</SUP>M<SUB>solar</SUB>, are possible progenitors of supermassive black holes in galactic nuclei. Because of their short nuclear burning time-scales, such objects can be formed only when matter is able to accumulate at a rate exceeding ~1M<SUB>solar</SUB>yr<SUP>-1</SUP>. Here we revisit the structure and evolution of rotationally stabilized supermassive stars, taking into account their continuous accumulation of mass and their thermal relaxation. We show that the outer layers of a supermassive star are not thermally relaxed during much of the star's main-sequence lifetime. As a result, they do not resemble n = 3 polytropes, as assumed in previous literature, but rather consist of convective (polytropic) cores surrounded by convectively stable envelopes that contain most of the mass. We compute the structures of these envelopes, in which the equation of state obeys P/ρ<SUP>4/3</SUP> ~ M<SUP>2/3</SUP>(R), where M(R) is the mass enclosed within radius R. By matching the envelope solutions to convective cores, we calculate the core mass as a function of time. We estimate the initial black hole masses formed as a result of core-collapse, and their subsequent growth via accretion from the bloated envelopes (`quasi-stars') that result. The seed black holes formed in this way could have typical masses in the range ~10<SUP>4</SUP>-10<SUP>5</SUP>M<SUB>solar</SUB>, considerably larger than the remnants thought to be left by the demise of Population III stars. Supermassive black holes therefore could have been seeded during an epoch of rapid infall considerably later than the era of Population III star formation.

[]

https://arxiv.org/pdf/0910.4398.pdf