Datasets:

ashishkgpian

/

astrorag_papers

like 0

2020JCAP...06..044D

Primordial black holes confront LIGO/Virgo data: current situation

2020-01-01

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

[]

The LIGO and Virgo Interferometers have so far provided 11 gravitational-wave (GW) observations of black-hole binaries. Similar detections are bound to become very frequent in the near future. With the current and upcoming wealth of data, it is possible to confront specific formation models with observations. We investigate here whether current data are compatible with the hypothesis that LIGO/Virgo black holes are of primordial origin. We compute in detail the mass and spin distributions of primordial black holes (PBHs), their merger rates, the stochastic background of unresolved coalescences, and confront them with current data from the first two observational runs, also including the recently discovered GW190412. We compute the best-fit values for the parameters of the PBH mass distribution at formation that are compatible with current GW data. In all cases, the maximum fraction of PBHs in dark matter is constrained by these observations to be f<SUB> PBH</SUB>≈ few× 10<SUP>-3</SUP>. We discuss the predictions of the PBH scenario that can be directly tested as new data become available. In the most likely formation scenarios where PBHs are born with negligible spin, the fact that at least one of the components of GW190412 is moderately spinning is incompatible with a primordial origin for this event, unless accretion or hierarchical mergers are significant. In the absence of accretion, current non-GW constraints already exclude that LIGO/Virgo events are all of primordial origin, whereas in the presence of accretion the GW bounds on the PBH abundance are the most stringent ones in the relevant mass range. A strong phase of accretion during the cosmic history would favour mass ratios close to unity, and a redshift-dependent correlation between high masses, high spins and nearly-equal mass binaries, with the secondary component spinning faster than the primary. Finally, we highlight that accretion can play an important role to relax current constraints on the PBH abundance, which calls for a better modelling of the mass and angular momentum accretion rates at redshift 0zlesssim3.

[]

https://arxiv.org/pdf/2005.05641.pdf

2018MNRAS.481.5445S

Black Hole Mergers From Globular Clusters Observable by LISA I: Eccentric Sources Originating From Relativistic N-body Dynamics

2018-01-01

['gravitation', 'gravitational waves', 'stars kinematics and dynamics', 'clusters globular', '-']

[]

We show that nearly half of all binary black hole (BBH) mergers dynamically assembled in globular clusters have measurable eccentricities (e &gt; 0.01) in the LISA band (10<SUP>-2</SUP> Hz), when General Relativistic corrections are properly included in the N-body evolution. If only Newtonian gravity is included, the derived fraction of eccentric LISA sources is significantly lower, which explains why recent studies all have greatly underestimated this fraction. Our findings have major implications for how to observationally distinguish between BBH formation channels using eccentricity with LISA, which is one of the key science goals of the mission. We illustrate that the relatively large population of eccentric LISA sources reported here originates from BBHs that merge between hardening binary-single interactions inside their globular cluster. These results indicate a bright future for using LISA to probe the origin of BBH mergers.

[]

https://arxiv.org/pdf/1804.06519.pdf

2021PhRvD.103f3538M

Threshold for primordial black holes. II. A simple analytic prescription

2021-01-01

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

[]

Primordial black holes could have been formed in the early universe from nonlinear cosmological perturbations reentering the cosmological horizon when the Universe was still radiation dominated. Starting from the shape of the power spectrum on superhorizon scales, we provide a simple prescription, based on the results of numerical simulations, to compute the threshold δ<SUB>c</SUB> for primordial black hole formation. Our procedure takes into account both the nonlinearities between the Gaussian curvature perturbation and the density contrast and, for the first time in the literature, the nonlinear effects arising at horizon crossing, which increase the value of the threshold by about a factor two with respect to the one computed on superhorizon scales.

[]

https://arxiv.org/pdf/2011.03014.pdf

2019MNRAS.488...47F

Black hole and neutron star mergers in galactic nuclei

2019-01-01

['stars kinematics and dynamics', '-', 'stars black holes', 'galaxy center', 'galaxy kinematics and dynamics', '-', '-', '-']

[]

Nuclear star clusters surrounding supermassive black holes (SMBHs) in galactic nuclei contain large numbers of stars, black holes (BHs), and neutron stars (NSs), a fraction of which are likely to form binaries. These binaries were suggested to form a triple system with the SMBH, which acts as a perturber and may enhance BH and NS mergers via the Lidov-Kozai mechanism. We follow-up previous studies, but for the first time perform an extensive statistical study of BH-BH, NS-NS, and BH-NS binary mergers by means of direct high-precision regularized N-body simulations, including post-Newtonian (PN) terms up to order PN2.5. We consider different SMBH masses, slopes for the BH mass function, binary semimajor axis and eccentricity distributions, and different spatial distributions for the binaries. We find that the merger rates are a decreasing function of the SMBH mass and are in the ranges ∼0.17-0.52, ∼0.06-0.10, and ∼0.04-0.16 Gpc<SUP>-3</SUP> yr<SUP>-1</SUP> for BH-BH, BH-NS, and NS-NS binaries, respectively. However, the rate estimate from this channel remains highly uncertain and depends on the specific assumptions regarding the star formation history in galactic nuclei and the supply rate of compact objects (COs). We find that {∼ } 10-20{{ per cent}} of the mergers enter the LIGO band with eccentricities ≳0.1. We also compare our results to the secular approximation, and show that N-body simulations generally predict a larger number of mergers. Finally, these events can also be observable via their electromagnetic counterparts, thus making these CO mergers especially valuable for cosmological and astrophysical purposes.

[]

https://arxiv.org/pdf/1811.10627.pdf

2000ApJ...536..668K

General Relativistic Simulations of Early Jet Formation in a Rapidly Rotating Black Hole Magnetosphere

2000-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxies jets', 'stars magnetic fields', 'methods numerical', 'mhd', 'relativity', 'astrophysics', '-']

[]

To investigate the formation mechanism of relativistic jets in active galactic nuclei and microquasars, we have developed a new general relativistic magnetohydrodynamic code in Kerr geometry. Here we report on the first numerical simulations of jet formation in a rapidly rotating (a=0.95) Kerr black hole magnetosphere. We study cases in which the Keplerian accretion disk is both corotating and counter-rotating with respect to the black hole rotation, and investigate the first ~50 light-crossing times. In the corotating disk case, our results are almost the same as those in Schwarzschild black hole cases: a gas pressure-driven jet is formed by a shock in the disk, and a weaker magnetically driven jet is also generated outside the gas pressure-driven jet. On the other hand, in the counter-rotating disk case, a new powerful magnetically driven jet is formed inside the gas pressure-driven jet. The newly found magnetically driven jet in the latter case is accelerated by a strong magnetic field created by frame dragging in the ergosphere. Through this process, the magnetic field extracts the energy of the black hole rotation.

[]

https://arxiv.org/pdf/astro-ph/9907435.pdf

2003CQGra..20L.277M

LETTER TO THE EDITOR: The black holes of topologically massive gravity

2003-01-01

['-', '-']

[]

We show that an analytical continuation of the Vuorio solution to three-dimensional topologically massive gravity leads to a two-parameter family of black-hole solutions, which are geodesically complete and causally regular within a certain parameter range. No observers can remain static in these spacetimes. We discuss their global structure, and evaluate their mass, angular momentum and entropy, which satisfy a slightly modified form of the first law of thermodynamics.

[]

https://arxiv.org/pdf/gr-qc/0303042.pdf

2008ApJ...673..703M

Comparing and Calibrating Black Hole Mass Estimators for Distant Active Galactic Nuclei

2008-01-01

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

[]

Black hole mass (M<SUB>BH</SUB>) is a fundamental property of active galactic nuclei (AGNs). In the distant universe, M<SUB>BH</SUB> is commonly estimated using the Mg II, Hβ, or Hα emission line widths and the optical/UV continuum or line luminosities as proxies for the characteristic velocity and size of the broad-line region. Although they all have a common calibration in the local universe, a number of different recipes are currently used in the literature. It is important to verify the relative accuracy and consistency of the recipes, as systematic changes could mimic evolutionary trends when comparing various samples. At z = 0.36, all three lines can be observed at optical wavelengths, providing a unique opportunity to compare different empirical recipes. We use spectra from the Keck Telescope and the Sloan Digital Sky Survey to compare M<SUB>BH</SUB> estimators for a sample of 19 AGNs at this redshift. We compare popular recipes available from the literature, finding that M<SUB>BH</SUB> estimates can differ up to 0.38 +/- 0.05 dex in the mean (or 0.13 +/- 0.05 dex, if the same virial coefficient is adopted). Finally, we provide a set of 30 internally self-consistent recipes for determining M<SUB>BH</SUB> from a variety of observables. The intrinsic scatter between cross-calibrated recipes is in the range 0.1-0.3 dex. This should be considered as a lower limit to the uncertainty of the M<SUB>BH</SUB> estimators.

[]

https://arxiv.org/pdf/0710.1839.pdf

2012ApJ...756...93H

Rapidly Accreting Supergiant Protostars: Embryos of Supermassive Black Holes?

2012-01-01

['accretion', 'accretion disks', 'cosmology theory', 'cosmology early universe', 'galaxies formation', 'stars fundamental parameters', '-', '-']

[]

Direct collapse of supermassive stars (SMSs) is a possible pathway for generating supermassive black holes in the early universe. It is expected that an SMS could form via very rapid mass accretion with \dot{M}_*\sim 0.1{--}1 \,M_\odot \,yr^{-1} during the gravitational collapse of an atomic-cooling primordial gas cloud. In this paper, we study how stars would evolve under such extreme rapid mass accretion, focusing on the early evolution until the stellar mass reaches 10<SUP>3</SUP> M <SUB>⊙</SUB>. To this end, we numerically calculate the detailed interior structure of accreting stars with primordial element abundances. Our results show that for accretion rates higher than 10<SUP>-2</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP>, stellar evolution is qualitatively different from that expected at lower rates. While accreting at these high rates, the star always has a radius exceeding 100 R <SUB>⊙</SUB>, which increases monotonically with the stellar mass. The mass-radius relation for stellar masses exceeding ~100 M <SUB>⊙</SUB> follows the same track with R <SUB>*</SUB>vpropM <SUP>1/2</SUP> <SUB>*</SUB> in all cases with accretion rates &gt;~ 10<SUP>-2</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP> at a stellar mass of 10<SUP>3</SUP> M <SUB>⊙</SUB>, the radius is ~= 7000 R <SUB>⊙</SUB> (sime 30 AU). With higher accretion rates, the onset of hydrogen burning is shifted toward higher stellar masses. In particular, for accretion rates exceeding \dot{M}_*\gtrsim 0.1 \,M_\odot \,yr^{-1}, there is no significant hydrogen burning even after 10<SUP>3</SUP> M <SUB>⊙</SUB> have accreted onto the protostar. Such "supergiant" protostars have effective temperatures as low as T <SUB>eff</SUB> ~= 5000 K throughout their evolution and because they hardly emit ionizing photons, they do not create an H II region or significantly heat their immediate surroundings. Thus, radiative feedback is unable to hinder the growth of rapidly accreting stars to masses in excess of 10<SUP>3</SUP> M <SUB>⊙</SUB> as long as material is accreted at rates \dot{M}_*\gtrsim 10^{-2} \,M_\odot \,yr^{-1}.

[]

https://arxiv.org/pdf/1203.2613.pdf

2011PhRvL.106l1301C

Universal Area Product Formulas for Rotating and Charged Black Holes in Four and Higher Dimensions

2011-01-01

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

[]

We present explicit results for the product of all horizon areas for general rotating multicharge black holes, both in asymptotically flat and asymptotically anti-de Sitter spacetimes in four and higher dimensions. The expressions are universal, and depend only on the quantized charges, quantized angular momenta and the cosmological constant. If the latter is also quantized these universal results may provide a “looking glass” for probing the microscopics of general black holes.

[]

https://arxiv.org/pdf/1011.0008.pdf

1999ApJ...520..650F

Merging White Dwarf/Black Hole Binaries and Gamma-Ray Bursts

1999-01-01

['accretion', 'accretion disks', 'black hole physics', 'gamma rays', 'hydrodynamics', 'stars white dwarfs', 'accretion', 'accretion disks', 'black hole physics', 'gamma rays', 'hydrodynamics', 'stars white dwarfs', 'astrophysics']

[]

The merger of compact binaries, especially black holes and neutron stars, is frequently invoked to explain gamma-ray bursts (GRBs). In this paper, we present three-dimensional hydrodynamical simulations of the relatively neglected mergers of white dwarfs and black holes. During the merger, the white dwarf is tidally disrupted and sheared into an accretion disk. Nuclear reactions are followed, and the energy release is negligible. Peak accretion rates are ~0.05 M<SUB>solar</SUB> s<SUP>-1</SUP> (less for lower mass white dwarfs) and last for approximately a minute. Many of the disk parameters can be explained by a simple analytic model that we derive and compare to our simulations. This model can be used to predict accretion rates for white dwarf and black hole (or neutron star) masses that are not simulated here. Although the mergers studied here create disks with larger radii and longer accretion times than those from the merger of double neutron stars, a larger fraction of the white dwarf's mass becomes part of the disk. Thus the merger of a white dwarf and a black hole could produce a long-duration GRB. The event rate of these mergers may be as high as 10<SUP>-6</SUP> yr<SUP>-1</SUP> per galaxy.

[]

https://arxiv.org/pdf/astro-ph/9808094.pdf

2004PhRvD..70l4006B

Quasinormal modes and classical wave propagation in analogue black holes

2004-01-01

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

[]

Many properties of black holes can be studied using acoustic analogues in the laboratory through the propagation of sound waves. We investigate in detail sound wave propagation in a rotating acoustic (2+1)-dimensional black hole, which corresponds to the “draining bathtub” fluid flow. We compute the quasinormal mode frequencies of this system and discuss late-time power-law tails. Because of the presence of an ergoregion, waves in a rotating acoustic black hole can be superradiantly amplified. We also compute superradiant reflection coefficients and instability time scales for the acoustic black hole bomb, the equivalent of the Press-Teukolsky black hole bomb. Finally we discuss quasinormal modes and late-time tails in a nonrotating canonical acoustic black hole, corresponding to an incompressible, spherically symmetric (3+1)-dimensional fluid flow.

[]

https://arxiv.org/pdf/gr-qc/0408099.pdf

1996PhRvL..77..430H

Statistical Entropy of Nonextremal Four-Dimensional Black Holes and U Duality

1996-01-01

['-', '-']

[]

We identify the states in string theory which are responsible for the entropy of near-extremal rotating four-dimensional black holes in N = 8 supergravity. For black holes far from extremality (with no rotation), the Bekenstein-Hawking entropy is exactly matched by a mysterious duality invariant extension of the formulas derived for near-extremal black holes states.

[]

https://arxiv.org/pdf/hep-th/9603195.pdf

2013PASJ...65..118S

Rotation Curve and Mass Distribution in the Galactic Center - From Black Hole to Entire Galaxy

2013-01-01

['galaxies', 'galaxies kinematics and dynamics', 'galaxies structure', 'ism kinematics and dynamics', 'astronomy radio', '-']

[]

Analyzing high-resolution longitude-velocity (LV) diagrams of the Galactic Center observed with the Nobeyama 45-m telescope in the CO and CS line emissions, we obtained a central rotation curve of the Milky Way. We combined it with data for the outer disk, and constructed a logarithmic rotation curve of the entire Galaxy. The new rotation curve covers a wide range of radius from r ∼ 1 pc to several hundred kpc without a gap of data points. It links, for the first time, the kinematical characteristics of the Galaxy from the central black hole to the bulge, disk and dark halo. Using this grand rotation curve, we calculated the radial distribution of the surface mass density in the entire Galaxy, where the radius and derived mass densities vary over a dynamical range with several orders of magnitudes. We show that the galactic bulge is deconvolved into two components: the inner (core) and main bulges. Both of the two bulge components are represented by exponential density profiles, but the de Vaucouleurs law was found to fail to represent the mass profile of the galactic bulge.

[]

https://arxiv.org/pdf/1307.8241.pdf

2006JHEP...09..021R

Noncommutative inspired black holes in extra dimensions

2006-01-01

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

[]

In a recent string theory motivated paper, Nicolini, Smailagic and Spallucci (NSS) presented an interesting model for a noncommutative inspired, Schwarzschild-like black hole solution in 4-dimensions. The essential effect of having noncommutative co-ordinates in this approach is to smear out matter distributions on a scale associated with the turn-on of noncommutativity which was taken to be near the 4-d Planck mass. In particular, NSS took this smearing to be essentially Gaussian. This energy scale is sufficiently large that in 4-d such effects may remain invisible indefinitely. Extra dimensional models which attempt to address the gauge hierarchy problem, however, allow for the possibility that the effective fundamental scale may not be far from ~ 1 TeV, an energy regime that will soon be probed by experiments at both the LHC and ILC. In this paper we generalize the NSS model to the case where flat, toroidally compactified extra dimensions are accessible at the Terascale and examine the resulting modifications in black hole properties due to the existence of noncommutativity. We show that while many of the noncommutativity-induced black hole features found in 4-d by NSS persist, in some cases there can be significant modifications due the presence of extra dimensions. We also demonstrate that the essential features of this approach are not particularly sensitive to the Gaussian nature of the smearing employed by NSS.

[]

https://arxiv.org/pdf/hep-ph/0606051.pdf

2012ApJ...748...36B

Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. I. Jet Energetics and the Pristine Parsec-scale Environment of a Supermassive Black Hole

2012-01-01

['galaxies nuclei', 'techniques interferometric', '-']

[]

We present continued radio observations of the tidal disruption event Swift J164449.3+573451 extending to δt ≈ 216 days after discovery. The data were obtained with the EVLA, AMI Large Array, CARMA, the SMA, and the VLBA+Effelsberg as part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and to trace the parsec-scale environment around a previously dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at δt ≈ 1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of ρvpropr <SUP>-3/2</SUP> (0.1-1.2 pc) with a significant flattening at r ≈ 0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an Lvpropt <SUP>-5/3</SUP> tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(&gt; Γ<SUB> j </SUB>)vpropΓ<SUP>-2.5</SUP> <SUB> j </SUB>. The similar ratios of duration to dynamical timescale for Sw 1644+57 and gamma-ray bursts (GRBs) suggest that this result may be applicable to GRB jets as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at r ~ 0.5 pc in good agreement with the Bondi radius for a ~few × 10<SUP>6</SUP> M <SUB>⊙</SUB> black hole. The density at ~0.5 pc is about a factor of 30 times lower than inferred for the Milky Way Galactic Center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations (δt ≈ 216 days) we find that the jet energy is E <SUB> j, iso</SUB> ≈ 5 × 10<SUP>53</SUP> erg (E<SUB>j</SUB> ≈ 2.4 × 10<SUP>51</SUP> erg for θ<SUB> j </SUB> = 0.1), the radius is r ≈ 1.2 pc, the Lorentz factor is Γ<SUB> j </SUB> ≈ 2.2, the ambient density is n ≈ 0.2 cm<SUP>-3</SUP>, and the projected angular size is r <SUB>proj</SUB> ≈ 25 μas, below the resolution of the VLBA+Effelsberg. Assuming no future changes in the observed evolution and a final integrated total energy of E<SUB>j</SUB> ≈ 10<SUP>52</SUP> erg, we predict that the radio emission from Sw 1644+57 should be detectable with the EVLA for several decades and will be resolvable with very long baseline interferometry in a few years.

[]

https://arxiv.org/pdf/1112.1697.pdf

2015MNRAS.447..948C

The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass

2015-01-01

['galaxy center', 'galaxy kinematics and dynamics', '-']

[]

We derive new constraints on the mass, rotation, orbit structure, and statistical parallax of the Galactic old nuclear star cluster and the mass of the supermassive black hole. We combine star counts and kinematic data from Fritz et al., including 2500 line-of-sight velocities and 10 000 proper motions obtained with VLT instruments. We show that the difference between the proper motion dispersions σ<SUB>l</SUB> and σ<SUB>b</SUB> cannot be explained by rotation, but is a consequence of the flattening of the nuclear cluster. We fit the surface density distribution of stars in the central 1000 arcsec by a superposition of a spheroidal cluster with scale ∼100 arcsec and a much larger nuclear disc component. We compute the self-consistent two-integral distribution function f(E, L<SUB>z</SUB>) for this density model, and add rotation self-consistently. We find that (i) the orbit structure of the f(E, L<SUB>z</SUB>) gives an excellent match to the observed velocity dispersion profiles as well as the proper motion and line-of-sight velocity histograms, including the double-peak in the v<SUB>l</SUB>-histograms. (ii) This requires an axial ratio near q<SUB>1</SUB> = 0.7 consistent with our determination from star counts, q<SUB>1</SUB> = 0.73 ± 0.04 for r &lt; 70 arcsec. (iii) The nuclear star cluster is approximately described by an isotropic rotator model. (iv) Using the corresponding Jeans equations to fit the proper motion and line-of-sight velocity dispersions, we obtain best estimates for the nuclear star cluster mass, black hole mass, and distance M<SUB>*</SUB>(r &lt; 100 arcsec) = (8.94 ± 0.31|<SUB>stat</SUB> ± 0.9|<SUB>syst</SUB>) × 10<SUP>6</SUP> M<SUB>⊙</SUB>, M<SUB>•</SUB> = (3.86 ± 0.14|<SUB>stat</SUB> ± 0.4|<SUB>syst</SUB>) × 10<SUP>6</SUP> M<SUB>⊙</SUB>, and R<SUB>0</SUB> = 8.27 ± 0.09|<SUB>stat</SUB> ± 0.1|<SUB>syst</SUB> kpc, where the estimated systematic errors account for additional uncertainties in the dynamical modelling. (v) The combination of the cluster dynamics with the S-star orbits around Sgr A* strongly reduces the degeneracy between black hole mass and Galactic Centre distance present in previous S-star studies. A joint statistical analysis with the results of Gillessen et al., gives M<SUB>•</SUB> = (4.23 ± 0.14) × 10<SUP>6</SUP> M<SUB>⊙</SUB> and R<SUB>0</SUB> = 8.33 ± 0.11 kpc.

[]

https://arxiv.org/pdf/1403.5266.pdf

2012PhRvD..86b4028B

Instabilities of wormholes and regular black holes supported by a phantom scalar field

2012-01-01

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

[]

We test the stability of various wormholes and black holes supported by a scalar field with a negative kinetic term. The general axial perturbations and the monopole type of polar perturbations are considered in the linear approximation. Two classes of objects are considered: (i) wormholes with flat asymptotic behavior at one end and anti-de Sitter on the other (Minkowski-anti-de Sitter wormholes) and (ii) regular black holes with asymptotically de Sitter expansion far beyond the horizon (the so-called black universes). A difficulty in such stability studies is that the effective potential for perturbations forms an infinite wall at throats, if any. Its regularization is in general possible only by numerical methods, and such a method is suggested in a general form and used in the present paper. As a result, we have shown that all configurations under study are unstable under spherically symmetric perturbations, except for a special class of black universes where the event horizon coincides with the minimum of the area function. For this stable family, the frequencies of quasinormal modes of axial perturbations are calculated.

[]

https://arxiv.org/pdf/1205.2224.pdf

2009PhRvD..80l4010S

Simulations of binary black hole mergers using spectral methods

2009-01-01

['-', '-', '-', '-', 'methods numerical', 'methods numerical', 'methods numerical', 'techniques spectroscopic', 'methods numerical', '-']

[]

Several improvements in numerical methods and gauge choice are presented that make it possible now to perform simulations of the merger and ringdown phases of “generic” binary black hole evolutions using the pseudospectral evolution code SpEC. These improvements include the use of a new damped-wave gauge condition, a new grid structure with appropriate filtering that improves stability, and better adaptivity in conforming the grid structures to the shapes and sizes of the black holes. Simulations illustrating the success of these new methods are presented for a variety of binary black hole systems. These include fairly generic systems with unequal masses (up to 2∶1 mass ratios), and spins (with magnitudes up to 0.4M<SUP>2</SUP>) pointing in various directions.

[]

https://arxiv.org/pdf/0909.3557.pdf

2021PhRvL.126a1104B

Spin-Induced Black Hole Scalarization in Einstein-Scalar-Gauss-Bonnet Theory

2021-01-01

['-', '-']

[]

We construct black hole solutions with spin-induced scalarization in a class of models where a scalar field is quadratically coupled to the topological Gauss-Bonnet term. Starting from the tachyonically unstable Kerr solutions, we obtain families of scalarized black holes such that the scalar field has either even or odd parity, and we investigate their domain of existence. The scalarized black holes can violate the Kerr rotation bound. We identify "critical" families of scalarized black hole solutions such that the expansion of the metric functions and of the scalar field at the horizon no longer allows for real coefficients. For the quadratic coupling considered here, solutions with spin-induced scalarization are entropically favored over Kerr solutions with the same mass and angular momentum.

[]

https://arxiv.org/pdf/2009.03905.pdf

2019ApJ...878...85S

Orbital Migration of Interacting Stellar Mass Black Holes in Disks around Supermassive Black Holes

2019-01-01

['accretion', 'accretion disks', 'black hole physics', 'galaxy nucleus', '-', '-']

[]

The merger rate of stellar-mass black hole binaries (sBHBs) inferred by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) suggests the need for an efficient source of sBHB formation. Active galactic nucleus (AGN) disks are a promising location for the formation of these sBHBs, as well as binaries of other compact objects, because of powerful torques exerted by the gas disk. These gas torques cause orbiting compact objects to migrate toward regions in the disk where inward and outward torques cancel, known as migration traps. We simulate the migration of stellar mass black holes in an example of a model AGN disk, using an augmented N-body code that includes analytic approximations to migration torques, stochastic gravitational forces exerted by turbulent density fluctuations in the disk, and inclination and eccentricity dampening produced by passages through the gas disk, in addition to the standard gravitational forces between objects. We find that sBHBs form rapidly in our model disk as stellar-mass black holes migrate toward the migration trap. These sBHBs are likely to subsequently merge on short timescales. The process continues, leading to the build-up of a population of over-massive stellar-mass black holes. The formation of sBHBs in AGN disks could contribute significantly to the sBHB merger rate inferred by LIGO.

[]

https://arxiv.org/pdf/1807.02859.pdf

2020ApJ...892...78K

Black Hole Parameter Estimation from Its Shadow

2020-01-01

['-', 'galaxy center', 'black hole physics', 'gravitation', 'gravitational lensing', '-', '-', '-', '-', '-', '-']

[]

The Event Horizon Telescope (EHT), a global submillimeter wavelength very long baseline interferometry array, unveiled event-horizon-scale images of the supermassive black hole M87* as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, and it is consistent with the shadow of a Kerr black hole of general relativity. A Kerr black hole is also a solution of some alternative theories of gravity, while several modified theories of gravity admit non-Kerr black holes. While earlier estimates for the M87* black hole mass, depending on the method used, fall in the range ≈ 3× 10<SUP>9</SUP> M<SUB>⊙</SUB> - 7×10<SUP>9</SUP> M<SUB>⊙</SUB>, the EHT data indicated a mass for the M87* black hole of (6.5 ± 0.7) × 10<SUP>9</SUP> M<SUB>⊙</SUB>. This offers another promising tool to estimate black hole parameters and to probe theories of gravity in its most extreme region near the event horizon. The important question arises: Is it possible by a simple technique to estimate black hole parameters from its shadow, for arbitrary models? In this paper, we present observables, expressed in terms of ordinary integrals, characterizing a haphazard shadow shape to estimate the parameters associated with black holes, and then illustrate its relevance to four different models: Kerr, Kerr-Newman, and two rotating regular models. Our method is robust, accurate, and consistent with the results obtained from existing formalism, and it is applicable to more general shadow shapes that may not be circular due to noisy data.

[]

https://arxiv.org/pdf/1811.01260.pdf

2000NuPhB.568...93D

Self-gravitating fundamental strings and black holes

2000-01-01

['-', '-']

[]

The configuration of typical highly excited ( M≫ M<SUB>s</SUB>∼( α') <SUP>-1/2</SUP>) string states is considered as the string coupling g is adiabatically increased. The size distribution of very massive single string states is studied and the mass shift, due to long-range gravitational, dilatonic and axionic attraction, is estimated. By combining the two effects, in any number of spatial dimensions d, the most probable size of a string state becomes of order ℓ <SUB>s</SUB>= 2 α' when g<SUP>2</SUP>M/ M<SUB>s</SUB>∼1. Depending on the dimension d, the transition between a random-walk-size string state (for low g) and a compact (∼ℓ <SUB>s</SUB>) string state (when g<SUP>2</SUP>M/ M<SUB>s</SUB>∼1) can be very gradual ( d=3), fast but continuous ( d=4), or discontinuous ( d⩾5). Those compact string states look like nuggets of an ultradense state of string matter, with energy density ρ∼ g<SUP>-2</SUP>M<SUB>s</SUB><SUP>d+1 </SUP>. Our results extend and clarify previous work by Susskind, and by Horowitz and Polchinski, on the correspondence between self-gravitating string states and black holes.

[]

https://arxiv.org/pdf/hep-th/9907030.pdf

2008PhRvD..78d1502C

Black hole thermodynamics from simulations of lattice Yang-Mills theory

2008-01-01

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

[]

We report on lattice simulations of 16 supercharge SU(N) Yang-Mills quantum mechanics in the ’t Hooft limit. Maldacena duality conjectures that in this limit the theory is dual to IIA string theory, and, in particular, that the behavior of the thermal theory at low temperature is equivalent to that of certain black holes in IIA supergravity. Our simulations probe the low temperature regime for N≤5 and the intermediate and high temperature regimes for N≤12. We observe ’t Hooft scaling, and at low temperatures our results are consistent with the dual black hole prediction. The intermediate temperature range is dual to the Horowitz-Polchinski correspondence region, and our results are consistent with continuous behavior there. We include the Pfaffian phase arising from the fermions in our calculations where appropriate.

[]

https://arxiv.org/pdf/0803.4273.pdf

2007ApJ...664L..79U

Suzaku Observations of Active Galactic Nuclei Detected in the Swift BAT Survey: Discovery of a ``New Type'' of Buried Supermassive Black Holes

2007-01-01

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

[]

We present the Suzaku broadband observations of two AGNs detected by the Swift BAT hard X-ray (&gt;15 keV) survey that did not have previous X-ray data, SWIFT J0601.9-8636 and SWIFT J0138.6-4001. The Suzaku spectra reveal in both objects a heavily absorbed power-law component with a column density of N<SUB>H</SUB>~=10<SUP>23.5</SUP>-10<SUP>24</SUP> cm<SUP>-2</SUP> that dominates above 10 keV and an intense reflection component with a solid angle &gt;~2π from a cold, optically thick medium. We find that these AGNs have an extremely small fraction of scattered light from the nucleus, &lt;~0.5% with respect to the intrinsic power-law component. This indicates that they are buried in a very geometrically thick torus with a small opening angle and/or have an unusually small amount of gas responsible for scattering. In the former case, the geometry of SWIFT J0601.9-8636 should be nearly face-on as inferred from the small absorption for the reflection component. The discovery of two such objects in this small sample implies that there must be a significant number of yet unrecognized, very Compton thick AGNs viewed at larger inclination angles in the local universe, which are difficult to detect even in the currently most sensitive optical or hard X-ray surveys.

[]

https://arxiv.org/pdf/0706.1168.pdf

2008PhRvD..77l4047B

Exploring black hole superkicks

2008-01-01

['-', '-', '-', '-', 'methods numerical', 'waves', '-', '-', '-']

[]

Recent calculations of the recoil velocity in black-hole binary mergers have found kick velocities of ≈2500km/s for equal-mass binaries with antialigned initial spins in the orbital plane. In general the dynamics of spinning black holes can be extremely complicated and are difficult to analyze and understand. In contrast, the “superkick” configuration is an example with a high degree of symmetry that also exhibits exciting physics. We exploit the simplicity of this test case to study more closely the role of spin in black-hole recoil and find that the recoil is with good accuracy proportional to the difference between the (l=2,m=±2) modes of Ψ<SUB>4</SUB>, the major contribution to the recoil occurs within 30M before and after the merger, and that this is after the time at which a standard post-Newtonian treatment breaks down. We also discuss consequences of the (l=2,m=±2) asymmetry in the gravitational wave signal for the angular dependence of the signal-to-noise ratio and the mismatch of the gravitational wave signals corresponding to the north and south poles.

[]

https://arxiv.org/pdf/0707.0135.pdf

2009CQGra..26j5015C

Warped AdS<SUB>3</SUB> black holes in new massive gravity

2009-01-01

['-', '-']

[]

We investigate stationary, rotationally symmetric solutions of a recently proposed three-dimensional theory of massive gravity. Along with BTZ black holes, we also obtain warped AdS<SUB>3</SUB> black holes, and (for a critical value of the cosmological constant) AdS<SUB>2</SUB> × S<SUP>1</SUP> as solutions. The entropy, mass and angular momentum of these black holes are computed.

[]

https://arxiv.org/pdf/0902.4634.pdf

2008ApJ...687L..25S

Three-Dimensional Simulations of Magnetized Thin Accretion Disks around Black Holes: Stress in the Plunging Region

2008-01-01

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

[]

We describe three-dimensional general relativistic magnetohydrodynamic simulations of a geometrically thin accretion disk around a nonspinning black hole. The disk has a thickness h/r ~ 0.05-0.1 over the radial range (2-20) GM/c<SUP>2</SUP>. In steady state, the specific angular momentum profile of the inflowing magnetized gas deviates by less than 2% from that of the standard thin disk model of Novikov and Thorne. Also, the magnetic torque at the radius of the innermost stable circular orbit (ISCO) is only ~2% of the inward flux of angular momentum at this radius. Both results indicate that magnetic coupling across the ISCO is relatively unimportant for geometrically thin disks.

[]

https://arxiv.org/pdf/0808.2860.pdf

1999PhRvD..59l4007P

Thermodynamics of Reissner-Nordström-anti-de Sitter black holes in the grand canonical ensemble

1999-01-01

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

[]

The thermodynamical properties of the Reissner-Nordström-anti-de Sitter black hole in the grand canonical ensemble are investigated using York's formalism. The black hole is enclosed in a cavity with a finite radius where the temperature and electrostatic potential are fixed. The boundary conditions allow one to compute the relevant thermodynamical quantities, e.g., thermal energy, entropy, and charge. The stability conditions imply that there are thermodynamically stable black hole solutions, under certain conditions. By taking the boundary to infinity, and leaving the event horizon and charge of the black hole fixed, one rederives the Hawking-Page action and Hawking-Page specific heat. Instantons with negative heat capacity are also found.

[]

https://arxiv.org/pdf/gr-qc/9805004.pdf

2004PhRvD..70j4016C

Excision boundary conditions for black-hole initial data

2004-01-01

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

[]

We define and extensively test a set of boundary conditions that can be applied at black-hole excision surfaces when the Hamiltonian and momentum constraints of general relativity are solved within the conformal thin-sandwich formalism. These boundary conditions have been designed to result in black holes that are in quasiequilibrium and are completely general in the sense that they can be applied with any conformal three-geometry and slicing condition. Furthermore, we show that they retain precisely the freedom to specify an arbitrary spin on each black hole. Interestingly, we have been unable to find a boundary condition on the lapse that can be derived from a quasiequilibrium condition. Rather, we find evidence that the lapse boundary condition is part of the initial temporal gauge choice. To test these boundary conditions, we have extensively explored the case of a single black hole and the case of a binary system of equal-mass black holes, including the computation of quasicircular orbits and the determination of the innermost stable circular orbit. Our tests show that the boundary conditions work well.

[]

https://arxiv.org/pdf/gr-qc/0407078.pdf

2005MNRAS.359.1469M

MCG-6-30-15: long time-scale X-ray variability, black hole mass and active galactic nuclei high states

2005-01-01

['black hole physics', 'galaxies active', 'galaxies', 'astronomy x rays', 'astronomy x rays', 'astrophysics']

[]

We present a detailed study of the long time-scale X-ray variability of the Seyfert 1 Galaxy MCG-6-30-15, based on eight years of frequent monitoring observations with the Rossi X-ray Timing Explorer. When combined with the published short-time-scale XMM-Newton observations, we derive the power-spectral density (PSD) covering six decades of frequency from ~10<SUP>-8</SUP> to ~10<SUP>-2</SUP> Hz. As with NGC 4051, another narrow-line Seyfert 1 galaxy (NLS1), we find that the PSD of MCG-6-30-15 is a close analogue of the PSD of a galactic black hole X-ray binary system (GBH) in a `high' rather than a `low' state. As with NGC 4051 and the GBH Cygnus X-1 in its high state, a smoothly bending model is a better fit to the PSD of MCG-6-30-15, giving a derived break frequency of 7.6<SUP>+10</SUP><SUB>-3</SUB>× 10<SUP>-5</SUP> Hz. Assuming linear scaling of the break frequency with black hole mass, we estimate the black hole mass in MCG-6-30-15 to be ~2.9<SUP>+1.8</SUP><SUB>-1.6</SUB>× 10<SUP>6</SUP>M<SUB>solar</SUB>. <P />Although, in the X-ray band, it is one of the best observed Seyfert galaxies, there has as yet been no accurate determination of the mass of the black hole in MCG-6-30-15. Here we present a mass determination using the velocity dispersion (M<SUB>BH</SUB>-σ<SUB>*</SUB>) technique and compare it with estimates based on the width of the Hα line. Depending on the calibration relationship assumed for the M<SUB>BH</SUB>-σ<SUB>*</SUB> relationship, we derive a mass of between 3.6 and 6 × 10<SUP>6</SUP>M<SUB>solar</SUB>, consistent with the mass derived from the PSD. <P />Using the newly derived mass and break time-scale, and revised reverberation masses for other active galactic nuclei (AGN) from Peterson et al., we update the black hole mass-break-time-scale diagram. The observations are still generally consistent with narrow-line Seyfert 1 galaxies having shorter break time-scales, for a given mass, than broad-line AGN, probably reflecting a higher accretion rate. However, the revised, generally higher, masses (but unchanged break time-scales) are also consistent with perhaps all of the X-ray bright AGN studied so far being high-state objects. This result may simply be a selection effect, based on their selection from high-flux X-ray all-sky catalogues, and their consequent typically high X-ray/radio ratios, which indicate high-state systems.

[]

https://arxiv.org/pdf/astro-ph/0503100.pdf

2020MNRAS.493.1888T

The relationship between black hole mass and galaxy properties: examining the black hole feedback model in IllustrisTNG

2020-01-01

['galaxies evolution', 'galaxies general', 'galaxies star clusters', '-']

[]

Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations between the specific star formation rate (sSFR), stellar mass (M<SUB>star</SUB>), and black hole mass (M<SUB>BH</SUB>) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and 10 model variations that alter the parameters of the black hole model. Focusing on central galaxies at z = 0 with M<SUB>star</SUB> &gt; 10<SUP>10</SUP> M<SUB>⊙</SUB>, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular M<SUB>BH</SUB> threshold above which galaxies are found to sharply transition from being mostly star forming to mostly quiescent. As a result of this behaviour, the fraction of quiescent galaxies as a function of M<SUB>star</SUB> is sensitive to both the normalization of the M<SUB>BH</SUB>-M<SUB>star</SUB> relation and the M<SUB>BH</SUB> threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M<SUB>BH</SUB> measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in M<SUB>BH</SUB> at a given M<SUB>star</SUB> and show a smoother decline in sSFR with M<SUB>BH</SUB>.

[]

https://arxiv.org/pdf/1906.02747.pdf

2019JCAP...07..048D

The ineludible non-Gaussianity of the primordial black hole abundance

2019-01-01

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

[]

We study the formation of primordial black holes when they are generated by the collapse of large overdensities in the early universe. Since the density contrast is related to the comoving curvature perturbation by a nonlinear relation, the overdensity statistics is unavoidably non-Gaussian. We show that the abundance of primordial black holes at formation may not be captured by a perturbative approach which retains the first few cumulants of the non-Gaussian probability distribution. We provide two techniques to calculate the non-Gaussian abundance of primordial black holes at formation, one based on peak theory and the other on threshold statistics. Our results show that the unavoidable non-Gaussian nature of the inhomogeneities in the energy density makes it harder to generate PBHs. We provide simple (semi-)analytical expressions to calculate the non-Gaussian abundances of the primordial black holes and show that for both narrow and broad power spectra the gaussian case from threshold statistics is reproduced by increasing the amplitude of the power spectrum by a factor Script O(2÷ 3).

[]

https://arxiv.org/pdf/1904.00970.pdf

2017PhRvD..96b3012T

Determining the population properties of spinning black holes

2017-01-01

['-']

[]

There are at least two formation scenarios consistent with the first gravitational-wave observations of binary black hole mergers. In field models, black hole binaries are formed from stellar binaries that may undergo common envelope evolution. In dynamic models, black hole binaries are formed through capture events in globular clusters. Both classes of models are subject to significant theoretical uncertainties. Nonetheless, the conventional wisdom holds that the distribution of spin orientations of dynamically merging black holes is nearly isotropic while field-model black holes prefer to spin in alignment with the orbital angular momentum. We present a framework in which observations of black hole mergers can be used to measure ensemble properties of black hole spin such as the typical black hole spin misalignment. We show how to obtain constraints on population hyperparameters using minimal assumptions so that the results are not strongly dependent on the uncertain physics of formation models. These data-driven constraints will facilitate tests of theoretical models and help determine the formation history of binary black holes using information encoded in their observed spins. We demonstrate that the ensemble properties of binary detections can be used to search for and characterize the properties of two distinct populations of black hole mergers.

[]

https://arxiv.org/pdf/1704.08370.pdf

2014EPJC...74.2836M

<inline-formula id="IEq1"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq2"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality of topological black holes in Lovelock–Born–Infeld gravity

2014-01-01

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

[]

To understand the effect of third order Lovelock gravity, <inline-formula id="IEq5"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq6"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality of topological AdS black holes in Lovelock–Born–Infeld gravity is investigated. The thermodynamics is further explored with some more extensions and in some more detail than the previous literature. A detailed analysis of the limit case <inline-formula id="IEq7"><mml:math><mml:mrow><mml:mi mathvariant="italic">β</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>∞</mml:mi></mml:mrow></mml:math></inline-formula> is performed for the seven-dimensional black holes. It is shown that, for the spherical topology, <inline-formula id="IEq8"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq9"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality exists for both the uncharged and the charged cases. Our results demonstrate again that the charge is not the indispensable condition of <inline-formula id="IEq10"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq11"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality. It may be attributed to the effect of higher derivative terms of the curvature because similar phenomenon was also found for Gauss–Bonnet black holes. For <inline-formula id="IEq12"><mml:math><mml:mrow><mml:mi>k</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow></mml:math></inline-formula>, there would be no <inline-formula id="IEq13"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq14"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality. Interesting findings occur in the case <inline-formula id="IEq15"><mml:math><mml:mrow><mml:mi>k</mml:mi><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math></inline-formula>, in which positive solutions of critical points are found for both the uncharged and the charged cases. However, the <inline-formula id="IEq16"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq17"><mml:math><mml:mi>v</mml:mi></mml:math></inline-formula> diagram is quite strange. To check whether these findings are physical, we give the analysis on the non-negative definiteness condition of the entropy. It is shown that, for any nontrivial value of <inline-formula id="IEq18"><mml:math><mml:mi mathvariant="italic">α</mml:mi></mml:math></inline-formula>, the entropy is always positive for any specific volume <inline-formula id="IEq19"><mml:math><mml:mi>v</mml:mi></mml:math></inline-formula>. Since no <inline-formula id="IEq20"><mml:math><mml:mi>P</mml:mi></mml:math></inline-formula>–<inline-formula id="IEq21"><mml:math><mml:mi>V</mml:mi></mml:math></inline-formula> criticality exists for <inline-formula id="IEq22"><mml:math><mml:mrow><mml:mi>k</mml:mi><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math></inline-formula> in Einstein gravity and Gauss–Bonnet gravity, we can relate our findings with the peculiar property of third order Lovelock gravity. The entropy in third order Lovelock gravity consists of extra terms which are absent in the Gauss–Bonnet black holes, which makes the critical points satisfy the constraint of non-negative definiteness condition of the entropy. We also check the Gibbs free energy graph and "swallow tail" behavior can be observed. Moreover, the effect of nonlinear electrodynamics is also included in our research.

[]

https://arxiv.org/pdf/1401.0785.pdf

2015PhRvD..92h3014M

Rotating black holes in Einstein-dilaton-Gauss-Bonnet gravity with finite coupling

2015-01-01

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

[]

Among various strong-curvature extensions of general relativity, Einstein-dilaton-Gauss-Bonnet gravity stands out as the only nontrivial theory containing quadratic curvature corrections while being free from the Ostrogradsky instability to any order in the coupling parameter. We derive an approximate stationary and axisymmetric black hole solution of this gravitational theory in closed form, which is of fifth order in the black hole spin and of seventh order in the coupling parameter of the theory. This extends previous work that obtained the corrections to the metric only to second order in the spin and at the leading order in the coupling parameter, and allows us to consider values of the coupling parameter close to the maximum permitted by theoretical constraints. We compute some quantities which characterize this solution, such as the dilaton charge, the moment of inertia, and the quadrupole moment, and its geodesic structure, including the innermost stable circular orbit and the epicyclic frequencies for massive particles. The latter provides a valuable tool to test general relativity against strong-curvature corrections through observations of the electromagnetic spectrum of accreting black holes.

[]

https://arxiv.org/pdf/1507.00680.pdf

2013JPhA...46u4001A

Black holes in three dimensional higher spin gravity: a review

2013-01-01

['-', '-']

[]

We review recent progress in the construction of black holes in three dimensional higher spin gravity theories. Starting from spin-3 gravity and working our way toward the theory of an infinite tower of higher spins coupled to matter, we show how to harness higher spin gauge invariance to consistently generalize familiar notions of black holes. We review the construction of black holes with conserved higher spin charges and the computation of their partition functions to leading asymptotic order. In view of the anti-de Sitter/conformal field theory (CFT) correspondence as applied to certain vector-like conformal field theories with extended conformal symmetry, we successfully compare to CFT calculations in a generalized Cardy regime. A brief recollection of pertinent aspects of ordinary gravity is also given. <P />This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Higher spin theories and holography’.

[]

https://arxiv.org/pdf/1208.5182.pdf

2016MNRAS.463.2323W

Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers

2016-01-01

['accretion', 'accretion disks', 'dense matter', 'gravitational waves', 'neutrinos', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', '-', '-', '-', '-', 'nuclear reactions;nucleosynthesis;abundances']

[]

We consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star-black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important - and in some cases dominant - contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second r-process peak (mass number A ∼ 130), independent of model parameters, with significant production of A &lt; 130 nuclei. This implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of r-process elements in metal poor stars. Disc outflows reach the third peak (A ∼ 195) in most of our simulations, although the amounts produced depend sensitively on the disc viscosity, initial mass or entropy of the torus, and nuclear physics inputs. Some of our models produce an abundance spike at A = 132 that is absent in the Solar system r-process distribution. The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. We conclude that disc outflows provide an important - and perhaps dominant - contribution to the r-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of r-process elements in the Galaxy.

[]

https://arxiv.org/pdf/1607.05290.pdf

2018JCAP...07..032B

Primordial black holes from inflation and quantum diffusion

2018-01-01

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

[]

Primordial black holes as dark matter may be generated in single-field models of inflation thanks to the enhancement at small scales of the comoving curvature perturbation. This mechanism requires leaving the slow-roll phase to enter a non-attractor phase during which the inflaton travels across a plateau and its velocity drops down exponentially. We argue that quantum diffusion has a significant impact on the primordial black hole mass fraction making the classical standard prediction not trustable.

[]

https://arxiv.org/pdf/1804.07124.pdf

2006PhRvD..73b4017A

Geometry of higher-dimensional black hole thermodynamics

2006-01-01

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

[]

We investigate thermodynamic curvatures of the Kerr and Reissner-Nordström (RN) black holes in spacetime dimensions higher than four. These black holes possess thermodynamic geometries similar to those in four-dimensional spacetime. The thermodynamic geometries are the Ruppeiner geometry and the conformally related Weinhold geometry. The Ruppeiner geometry for a d=5 Kerr black hole is curved and divergent in the extremal limit. For a d≥6 Kerr black hole there is no extremality but the Ruppeiner curvature diverges where one suspects that the black hole becomes unstable. The Weinhold geometry of the Kerr black hole in arbitrary dimension is a flat geometry. For the RN black hole the Ruppeiner geometry is flat in all spacetime dimensions, whereas its Weinhold geometry is curved. In d≥5 the Kerr black hole can possess more than one angular momentum. Finally we discuss the Ruppeiner geometry for the Kerr black hole in d=5 with double angular momenta.

[]

https://arxiv.org/pdf/hep-th/0510139.pdf

2007ApJ...667..704V

Black Hole Spin and Galactic Morphology

2007-01-01

['black hole physics', 'cosmology theory', 'galaxies evolution', 'galaxies quasars', 'astrophysics']

[]

We investigate the conjecture by Sikora, Stawarz, and Lasota that the observed active galactic nuclei (AGNs) radio loudness bimodality can be explained by the morphology-related bimodality of black hole spin distribution in the centers of galaxies: central black holes (BHs) in giant elliptical galaxies may have (on average) much larger spins than black holes in spiral/disk galaxies. We study how accretion from a warped disk influences the evolution of black hole spins and conclude that within the cosmological framework, where the most massive BHs have grown in mass via merger-driven accretion, one indeed expects most supermassive black holes in elliptical galaxies to have on average higher spin than black holes in spiral galaxies, where random, small accretion episodes (e.g., tidally disrupted stars, accretion of molecular clouds) might have played a more important role.

[]

https://arxiv.org/pdf/0706.3900.pdf

2018PhRvD..97j4062P

Black hole shadow in an expanding universe with a cosmological constant

2018-01-01

['-']

[]

We analytically investigate the influence of a cosmic expansion on the shadow of the Schwarzschild black hole. We suppose that the expansion is driven by a cosmological constant only and use the Kottler (or Schwarzschild-de Sitter) spacetime as a model for a Schwarzschild black hole embedded in a de Sitter universe. We calculate the angular radius of the shadow for an observer who is comoving with the cosmic expansion. It is found that the angular radius of the shadow shrinks to a nonzero finite value if the comoving observer approaches infinity.

[]

https://arxiv.org/pdf/1804.04898.pdf

1998ApJ...492L..53C

Evidence for Frame Dragging around Spinning Black Holes in X-Ray Binaries

1998-01-01

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

[]

In the context of black hole spin in X-ray binaries, we propose that certain types of quasi-periodic oscillations (QPOs) observed in the light curves of black hole binaries (BHBs) are produced by X-ray modulation at the precession frequency of accretion disks, because of relativistic dragging of inertial frames around spinning black holes. These QPOs tend to be relatively stable in their centroid frequencies. They have been observed in the frequency range of a few hertz to a few hundred hertz for several black holes with dynamically determined masses. By comparing the computed disk precession frequency with that of the observed QPO, we can derive the black hole spin, given its mass. When applying this model to GRO J1655-40, GRS 1915+105, Cyg X-1, and GS 1124-68, we found that the black holes in GRO J1655-40 and GRS 1915+105, the only known BHBs that occasionally produce superluminal radio jets, spin at a rate close to the maximum limit, while Cyg X-1 and GS 1124-68, typical (persistent and transient) BHBs, contain only moderately rotating ones. Extending the model to the general population of black hole candidates, the fact that only low-frequency QPOs have been detected is consistent with the presence of only slowly spinning black holes in these systems. Our results are in good agreement with those derived from spectral data, thus strongly supporting the classification scheme that we proposed previously for BHBs.

[]

https://arxiv.org/pdf/astro-ph/9710352.pdf

1997PThPS.128....1M

Chapter 1. Black Hole Perturbation

1997-01-01

['-']

[]

In this chapter, we present analytic calculations of gravitational waves from a particle orbiting a black hole. We first review the Teukolsky formalism for dealing with the gravitational perturbation of a black hole. Then we develop a systematic method to calculate higher order post-Newtonian corrections to the gravitational waves emitted by an orbiting particle. As applications of this method, we consider orbits that are nearly circular, including exactly circular ones, slightly eccentric ones and slightly inclined orbits off the equatorial plane of a Kerr black hole and give the energy flux and angular momentum flux formulas at infinity with higher order post-Newtonian corrections. Using a different method that makes use of an analytic series representation of the solution of the Teukolsky equation, we also give a post-Newtonian expanded formula for the energy flux absorbed by a Kerr black hole for a circular orbit.

[]

https://arxiv.org/pdf/gr-qc/9712057.pdf

2011ApJ...742..107B

The Relation between Black Hole Mass and Host Spheroid Stellar Mass Out to z ~ 2

2011-01-01

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

[]

We combine Hubble Space Telescope images from the Great Observatories Origins Deep Survey with archival Very Large Telescope and Keck spectra of a sample of 11 X-ray-selected broad-line active galactic nuclei in the redshift range 1 &lt; z &lt; 2 to study the black-hole-mass-stellar-mass relation out to a look-back time of 10 Gyr. Stellar masses of the spheroidal component (M <SUB>sph, sstarf</SUB>) are derived from multi-filter surface photometry. Black hole masses (M <SUB>BH</SUB>) are estimated from the width of the broad Mg II emission line and the 3000 Å nuclear luminosity. Comparing with a uniformly measured local sample and taking into account selection effects, we find evolution in the form M <SUB>BH</SUB>/M <SUB>sph, sstarf</SUB>vprop(1 + z)<SUP>1.96 ± 0.55</SUP>, in agreement with our earlier studies based on spheroid luminosity. However, this result is more accurate because it does not require a correction for luminosity evolution and therefore avoids the related and dominant systematic uncertainty. We also measure total stellar masses (M <SUB>host, sstarf</SUB>). Combining our sample with data from the literature, we find M <SUB>BH</SUB>/M <SUB>host, sstarf</SUB>vprop(1 + z)<SUP>1.15 ± 0.15</SUP>, consistent with the hypothesis that black holes (in the range M <SUB>BH</SUB> ~ 10<SUP>8-9</SUP> M <SUB>⊙</SUB>) pre-date the formation of their host galaxies. Roughly, one-third of our objects reside in spiral galaxies; none of the host galaxies reveal signs of interaction or major merger activity. Combined with the slower evolution in host stellar masses compared to spheroid stellar masses, our results indicate that secular evolution or minor mergers play a non-negligible role in growing both BHs and spheroids.

[]

https://arxiv.org/pdf/1102.1975.pdf

2007PhRvD..75j6001H

Local bulk operators in AdS/CFT correspondence: A holographic description of the black hole interior

2007-01-01

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

[]

To gain insight into how bulk locality emerges from the holographic conformal field theory (CFT), we reformulate the bulk-to-boundary map in as local a way as possible. In previous work, we carried out this program for Lorentzian anti-de Sitter (AdS), and showed the support on the boundary could always be reduced to a compact region spacelike separated from the bulk point. In the present work the idea is extended to a complexified boundary, where spatial coordinates are continued to imaginary values. This continuation enables us to represent a local bulk operator as a CFT operator with support on a finite disc on the complexified boundary. We treat general AdS in Poincaré coordinates and AdS<SUB>3</SUB> in Rindler coordinates. We represent bulk operators inside the horizon of a Banados-Teitelboim-Zanelli (BTZ) black hole and we verify that the correct bulk two-point functions are reproduced, including the divergence when one point hits the BTZ singularity. We comment on the holographic description of black holes formed by collapse and discuss locality and holographic entropy counting at finite N.

[]

https://arxiv.org/pdf/hep-th/0612053.pdf

1997NuPhB.486...77D

BPS spectrum of the five-brane and black hole entropy

1997-01-01

['-']

[]

We propose a formulation of ]]-dimensional M-theory in terms of five-branes with closed strings on their world-volume. We use this description to construct the complete spectrum of BPS states in compactifications to six and five dimensions. We compute the degeneracy for fixed charge and find it to be in accordance with U-duality (which in our formulation is manifest in six dimensions) and the statistical entropy formula of the corresponding black hole. We also briefly comment on the compactification to four dimensions.

[]

https://arxiv.org/pdf/hep-th/9603126.pdf

2005ApJ...629..362H

The Orbital Statistics of Stellar Inspiral and Relaxation near a Massive Black Hole: Characterizing Gravitational Wave Sources

2005-01-01

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

[]

We study the orbital parameter distribution of stars that are scattered into nearly radial orbits and then spiral into a massive black hole (MBH) due to dissipation, in particular by emission of gravitational waves (GWs). This is important for GW detection, e.g., by the Laser Interferometer Space Antenna (LISA). Signal identification requires knowledge of the waveforms, which depend on the orbital parameters. We use analytical and Monte Carlo methods to analyze the interplay between GW dissipation and scattering in the presence of a mass sink during the transition from the initial scattering-dominated phase to the final dissipation-dominated phase of the inspiral. Our main results are as follows. (1) Stars typically enter the GW-emitting phase with high eccentricities. (2) The GW event rate per galaxy is afew×10<SUP>-9</SUP> yr<SUP>-1</SUP> for typical central stellar cusps, almost independently of the relaxation time or the MBH mass. (3) For intermediate-mass black holes of ~10<SUP>3</SUP> M<SUB>solar</SUB> such as may exist in dense stellar clusters, the orbits are very eccentric and the inspiral is rapid, so the sources are very short-lived.

[]

https://arxiv.org/pdf/astro-ph/0503672.pdf

2002PhRvD..65d4021G

Binary black holes in circular orbits. II. Numerical methods and first results

2002-01-01

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

[]

We present the first results from a new method for computing spacetimes representing corotating binary black holes in circular orbits. The method is based on the assumption of exact equilibrium. It uses the standard 3+1 decomposition of Einstein equations and conformal flatness approximation for the 3-metric. Contrary to previous numerical approaches to this problem, we do not solve only the constraint equations but rather a set of five equations for the lapse function, the conformal factor and the shift vector. The orbital velocity is unambiguously determined by imposing that, at infinity, the metric behaves like the Schwarzschild one, a requirement which is equivalent to the virial theorem. The numerical scheme has been implemented using multi-domain spectral methods and passed numerous tests. A sequence of corotating black holes of equal mass is calculated. Defining the sequence by requiring that the ADM mass decrease is equal to the angular momentum decrease multiplied by the orbital angular velocity, it is found that the area of the apparent horizons is constant along the sequence. We also find a turning point in the ADM mass and angular momentum curves, which may be interpreted as an innermost stable circular orbit (ISCO). The values of the global quantities at the ISCO, especially the orbital velocity, are in much better agreement with those from third post-Newtonian calculations than with those resulting from previous numerical approaches.

[]

https://arxiv.org/pdf/gr-qc/0106016.pdf

2009ApJ...701.1175S

X-ray Polarization from Accreting Black Holes: The Thermal State

2009-01-01

['black hole physics', 'polarization', 'radiative transfer', 'astronomy x rays', '-']

[]

We present new calculations of X-ray polarization from black hole (BH) accretion disks in the thermally dominated state, using a Monte Carlo ray-tracing code in full general relativity. In contrast to many previously published studies, our approach allows us to include returning radiation that is deflected by the strong-field gravity of the BH and scatters off of the disk before reaching a distant observer. Although carrying a relatively small fraction of the total observed flux, the scattered radiation tends to be highly polarized and in a direction perpendicular to the direct radiation Agol &amp; Krolik. For moderately large spin parameters (a/M gsim 0.9), this scattered returning radiation dominates the polarization signal at energies above the thermal peak, giving a net rotation in the polarization angle of 90°. We show how these new features of the polarization spectra from BHs in the thermal state may be developed into a powerful tool for measuring BH spin and probing the gas flow in the innermost disk. In addition to determining the emission profile, polarization observations can be used to constrain other properties of the system such as BH mass, inclination, and distance. New instruments currently under development should be able to exploit this tool in the near future.

[]

https://arxiv.org/pdf/0902.3982.pdf

2016MNRAS.457.2122G

Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes

2016-01-01

['-']

[]

Galactic nuclei typically host either a Nuclear Star Cluster (NSC, prevalent in galaxies with masses $\lesssim 10^{10}M_\odot$) or a Massive Black Hole (MBH, common in galaxies with masses $\gtrsim 10^{12}M_\odot$). In the intermediate mass range, some nuclei host both a NSC and a MBH. In this paper, we explore scaling relations between NSC mass (${\cal M}_{\rm NSC}$) and host galaxy total stellar mass (${\cal M}_{\star,\rm gal}$) using a large sample of NSCs in late- and early-type galaxies, including a number of NSCs harboring a MBH. Such scaling relations reflect the underlying physical mechanisms driving the formation and (co)evolution of these central massive objects. We find $\sim\!1.5\sigma$ significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations $r_{\rm eff,NSC}$--${\cal M}_{\rm NSC}$, $r_{\rm eff, NSC}$--${\cal M}_{\star,\rm gal}$ and ${\cal M}_{\rm NSC}$--${\cal M}_{\star,\rm gal}$, in the sense that $i)$ NSCs in late-types are more compact at fixed ${\cal M}_{\rm NSC}$ and ${\cal M}_{\star,\rm gal}$; and $ii)$ the ${\cal M}_{\rm NSC}$--${\cal M}_{\star,\rm gal}$ relation is shallower for NSCs in late-types than in early-types, similar to the ${\cal M}_{\rm BH}$--${\cal M}_{\star,\rm bulge}$ relation. We discuss these results in the context of the (possibly ongoing) evolution of NSCs, depending on host galaxy type. For NSCs with a MBH, we illustrate the possible influence of a MBH on its host NSC, by considering the ratio between the radius of the MBH sphere of influence and $r_{\rm eff, NSC}$. NSCs harbouring a sufficiently massive black hole are likely to exhibit surface brightness profile deviating from a typical King profile.

[]

https://arxiv.org/pdf/1601.02613.pdf

2005MNRAS.359..801K

Observations of the Blandford-Znajek process and the magnetohydrodynamic Penrose process in computer simulations of black hole magnetospheres

2005-01-01

['black hole physics', 'stars magnetic fields', 'methods numerical', 'astrophysics']

[]

In this paper we report the results of axisymmetric relativistic magnetohydrodynamic (MHD) simulations for the problem of a Kerr black hole immersed in a rarefied plasma with `uniform' magnetic field. The long-term solution shows properties that are significantly different from those of the initial transient phase studied recently by Koide. The topology of magnetic field lines within the ergosphere is similar to that of the split-monopole model with a strong current sheet in the equatorial plane. Closer inspection reveals a system of isolated magnetic islands inside the sheet and ongoing magnetic reconnection. No regions of negative hydrodynamic `energy at infinity' are seen inside the ergosphere and the so-called MHD Penrose process does not operate. However, the rotational energy of the black hole continues to be extracted via the purely electromagnetic Blandford-Znajek mechanism. In spite of this, no strong relativistic outflows from the black hole are seen to be developing. Combined with results of other recent simulations, our results signal a potential problem for the standard MHD model of relativistic astrophysical jets should they be found at distances as small as a few tens of gravitational radii from the central black hole.

[]

https://arxiv.org/pdf/astro-ph/0501599.pdf

2013PhRvD..87f3519K

Primordial black hole formation from an axionlike curvaton model

2013-01-01

['-', '-', '-', 'particles', '-', 'cosmology dark matter', '-', '-']

[]

We argue that the existence of the cold dark matter is explained by primordial black holes. We show that a significant number of primordial black holes can be formed in an axionlike curvaton model, in which the highly blue-tilted power spectrum of primordial curvature perturbations is achieved. It is found that the produced black holes with masses ∼10<SUP>20</SUP>-10<SUP>38</SUP>g account for the present cold dark matter. We also argue the possibility of forming the primordial black holes with mass ∼10<SUP>5</SUP>M<SUB>⊙</SUB> as seeds of the supermassive black holes.

[]

https://arxiv.org/pdf/1207.2550.pdf

2014CQGra..31a5002J

Distinguishing black holes from naked singularities through their accretion disc properties

2014-01-01

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

[]

We show that, in principle, a slowly evolving gravitationally collapsing perfect fluid cloud can asymptotically settle to a static spherically symmetric equilibrium configuration with a naked singularity at the center. We consider one such asymptotic final configuration with a finite outer radius, and construct a toy model in which it is matched to a Schwarzschild exterior geometry. We examine the properties of circular orbits in this model. We then investigate the observational signatures of a thermal accretion disc in this spacetime, comparing them with the signatures expected for a disc around a black hole of the same mass. Several notable differences emerge. A disc around the naked singularity is much more luminous than one around an equivalent black hole. Also, the disc around the naked singularity has a spectrum with a high frequency power law segment that carries a major fraction of the total luminosity. Thus, at least some naked singularities can, in principle, be distinguished observationally from the black holes of the same mass. We discuss the possible implications of these results.

[]

https://arxiv.org/pdf/1304.7331.pdf

2013CQGra..30x4004R

The spin of supermassive black holes

2013-01-01

['-', '-']

[]

Black hole spin is a quantity of great interest to both physicists and astrophysicists. We review the current status of spin measurements in supermassive black holes (SMBH). To date, every robust SMBH spin measurement uses x-ray reflection spectroscopy, so we focus almost exclusively on this technique as applied to moderately-luminous active galactic nuclei (AGN). After describing the foundations and uncertainties of the method, we summarize the current status of the field. At the time of writing, observations by XMM-Newton, Suzaku and NuSTAR have given robust spin constraints on 22 SMBHs. We find a significant number of rapidly rotating SMBHs (with dimensionless spin parameters a &gt; 0.9) although, especially at the higher masses (M &gt; 4 × 10<SUP>7</SUP>M<SUB>⊙</SUB>), there are also some SMBHs with intermediate spin parameters. This may be giving us our first hint at a mass-dependent spin distribution which would, in turn, provide interesting constraints on models for SMBH growth. We also discuss the recent discovery of relativistic x-ray reverberation which we can use to ‘echo map’ the innermost regions of the accretion disc. The ultimate development of these reverberation techniques, when applied to data from future high-throughput x-ray observatories such as LOFT, ATHENA+, and AXSIO, will permit the measurement of black hole spin by a characterization of strong-field Shapiro delays. We conclude with a brief discussion of other electromagnetic methods that have been attempted or are being developed to constrain SMBH spin.

[]

https://arxiv.org/pdf/1307.3246.pdf

2014PhRvD..90b4026F

Neutron star-black hole mergers with a nuclear equation of state and neutrino cooling: Dependence in the binary parameters

2014-01-01

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

[]

We present a first exploration of the results of neutron star-black hole mergers using black hole masses in the most likely range of 7M⊙-10M<SUB>⊙</SUB>, a neutrino leakage scheme, and a modeling of the neutron star material through a finite-temperature nuclear-theory based equation of state. In the range of black hole spins in which the neutron star is tidally disrupted (χ<SUB>BH</SUB>≳0.7), we show that the merger consistently produces large amounts of cool (T ≲1 MeV), unbound, neutron-rich material (M<SUB>ej</SUB>∼0.05M<SUB>⊙</SUB>-0.20M⊙). A comparable amount of bound matter is initially divided between a hot disk (T<SUB>max</SUB>∼15 MeV) with typical neutrino luminosity of L<SUB>ν</SUB>∼<SUP>1053</SUP> erg /s, and a cooler tidal tail. After a short period of rapid protonization of the disk lasting ∼10 ms, the accretion disk cools down under the combined effects of the fall-back of cool material from the tail, continued accretion of the hottest material onto the black hole, and neutrino emission. As the temperature decreases, the disk progressively becomes more neutron rich, with dimmer neutrino emission. This cooling process should stop once the viscous heating in the disk (not included in our simulations) balances the cooling. These mergers of neutron star-black hole binaries with black hole masses of M<SUB>BH</SUB>∼7M⊙-10M⊙, and black hole spins high enough for the neutron star to disrupt provide promising candidates for the production of short gamma-ray bursts, of bright infrared postmerger signals due to the radioactive decay of unbound material, and of large amounts of r-process nuclei.

[]

https://arxiv.org/pdf/1405.1121.pdf

2019PhRvD..99j3531W

Prospective constraints on the primordial black hole abundance from the stochastic gravitational-wave backgrounds produced by coalescing events and curvature perturbations

2019-01-01

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

[]

For a variety of ongoing and planned gravitational-wave (GW) experiments, we study expected constraints on the fraction (f<SUB>PBH</SUB>) of primordial black holes (PBHs) in dark matter by evaluating the energy-density spectra of two kinds of stochastic GW backgrounds. The first one is produced from an incoherent superposition of GWs emitted from coalescences of all of the binary PBHs. The second one is induced through nonlinear mode couplings of large primordial curvature perturbations inevitably associated with the generation of PBHs in the early Universe. In this paper, we focus on PBHs with masses 10<SUP>-8</SUP> M<SUB>⊙</SUB>≤M<SUB>PBH</SUB>&lt;1 M<SUB>⊙</SUB> , since they are not expected to be of stellar origin. In almost all mass ranges, we show that the experiments are sensitive enough to constrain the fraction for 10<SUP>-5</SUP>≲f<SUB>PBH</SUB>≲1 by considering the GWs from coalescing events and 10<SUP>-10</SUP>≲f<SUB>PBH</SUB>≲1 by considering the GWs from curvature perturbations. Exceptionally, the fraction cannot be constrained for f<SUB>PBH</SUB>≲3 ×10<SUP>-3</SUP> by these two GW backgrounds only in the narrow mass range 2 ×10<SUP>-5</SUP> M<SUB>⊙</SUB>≲M<SUB>PBH</SUB>≲4 ×10<SUP>-5</SUP> M<SUB>⊙</SUB> .

[]

https://arxiv.org/pdf/1903.05924.pdf

2019PhRvD..99f4011S

Stability of scalarized black hole solutions in scalar-Gauss-Bonnet gravity

2019-01-01

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

[]

Scalar-tensor theories of gravity where a new scalar degree of freedom couples to the Gauss-Bonnet invariant can exhibit the phenomenon of spontaneous black hole scalarization. These theories admit both the classic black hole solutions predicted by general relativity as well as novel hairy black hole solutions. The stability of hairy black holes is strongly dependent on the precise form of the scalar-gravity coupling. A radial stability investigation revealed that all scalarized black hole solutions are unstable when the coupling between the scalar field and the Gauss-Bonnet invariant is quadratic in the scalar, whereas stable solutions exist for exponential couplings. Here, we elucidate this behavior. We demonstrate that, while the quadratic term controls the onset of the tachyonic instability that gives rise to the black hole hair, the higher-order coupling terms control the nonlinearities that quench that instability and, hence, also control the stability of the hairy black hole solutions.

[]

https://arxiv.org/pdf/1812.05590.pdf

2014PhLB..730...14B

Regular black hole metrics and the weak energy condition

2014-01-01

['-']

[]

In this work we construct a family of spherically symmetric, static, charged regular black hole metrics in the context of Einstein-nonlinear electrodynamics theory. The construction of the charged regular black hole metrics is based on three requirements: (a) the weak energy condition should be satisfied, (b) the energy-momentum tensor should have the symmetry T00=T11, and (c) these metrics have to asymptotically behave as the Reissner-Nordström black hole metric. In addition, these charged regular black hole metrics depend on two parameters which for specific values yield regular black hole metrics that already exist in the literature. Furthermore, by relaxing the third requirement, we construct more general regular black hole metrics which do not behave asymptotically as a Reissner-Nordström black hole metric.

[]

https://arxiv.org/pdf/1401.2136.pdf

2013A&A...558A..59S

Massive black hole factories: Supermassive and quasi-star formation in primordial halos

2013-01-01

['cosmology theory', '-', '-', '-', '-', 'stars fundamental parameters', '-']

[]

Context. Supermassive stars and quasi-stars (massive stars with a central black hole) are both considered as potential progenitors for the formation of supermassive black holes. They are expected to form from rapidly accreting protostars in massive primordial halos. <BR /> Aims: We explore how long rapidly accreting protostars remain on the Hayashi track, implying large protostellar radii and weak accretion luminosity feedback. We assess the potential role of energy production in the nuclear core, and determine what regulates the evolution of such protostars into quasi-stars or supermassive stars. <BR /> Methods: We followed the contraction of characteristic mass shells in rapidly accreting protostars, and inferred the timescales for them to reach nuclear densities. We compared the characteristic timescales for nuclear burning with those for which the extended protostellar envelope can be maintained. <BR /> Results: We find that the extended envelope can be maintained up to protostellar masses of 3.6 × 10<SUP>8</SUP> ṁ<SUP>3</SUP> M<SUB>⊙</SUB>, where ṁ denotes the accretion rate in solar masses per year. We expect the nuclear core to exhaust its hydrogen content in 7 × 10<SUP>6</SUP> yr. If accretion rates ṁ ≫ 0.14 can still be maintained at this point, a black hole may form within the accreting envelope, leading to a quasi-star. Alternatively, the accreting object will gravitationally contract to become a main-sequence supermassive star. <BR /> Conclusions: Due to the limited gas reservoir in typical 10<SUP>7</SUP> M<SUB>⊙</SUB> dark matter halos, the accretion rate onto the central object may drop at late times, implying the formation of supermassive stars as the typical outcome of direct collapse. However, if high accretion rates are maintained, a quasi-star with an interior black hole may form.

[]

https://arxiv.org/pdf/1305.5923.pdf

2014ApJ...780...86E

Nuclear Star Formation Activity and Black Hole Accretion in Nearby Seyfert Galaxies

2014-01-01

['galaxies nuclei', 'galaxies seyfert', 'astronomy infrared', '-']

[]

Recent theoretical and observational works indicate the presence of a correlation between the star-formation rate (SFR) and active galactic nucleus (AGN) luminosity (and, therefore, the black hole accretion rate, \dot{M}_BH) of Seyfert galaxies. This suggests a physical connection between the gas-forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (~0.''4-0.''8) mid-infrared (8-13 μm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalog. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of ~65 pc (median value). We found no general evidence of suppression of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and we used this feature as a proxy for the SFR. We detected the 11.3 μm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22 M <SUB>⊙</SUB> yr<SUP>-1</SUP> kpc<SUP>-2</SUP>) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ~65 pc region of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and \dot{M}_BH and showed that numerical simulations reproduce our observed relation fairly well.

[]

https://arxiv.org/pdf/1311.0703.pdf

2021PhLB..81336040K

Solar-mass primordial black holes explain NANOGrav hint of gravitational waves

2021-01-01

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

[]

The NANOGrav collaboration for the pulsar timing array (PTA) observation recently announced evidence of an isotropic stochastic process, which may be the first detection of the stochastic gravitational-wave (GW) background. We discuss the possibility that the signal is caused by the second-order GWs associated with the formation of solar-mass primordial black holes (PBHs). This possibility can be tested by future interferometer-type GW observations targeting the stochastic GWs from merger events of solar-mass PBHs as well as by updates of PTA observations.

[]

https://arxiv.org/pdf/2009.11853.pdf

2000ApJ...544..993S

Complete RXTE Spectral Observations of the Black Hole X-ray Nova XTE J1550-564

2000-01-01

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

[]

We report on the X-ray spectral behavior of XTE J1550-564 during its 1998-1999 outburst. XTE J1550-564 is an exceptionally bright X-ray nova and is also the third Galactic black hole candidate known to exhibit quasi-periodic X-ray oscillations above 50 Hz. Our study is based on 209 pointed observations using the PCA and HEXTE instruments on board the Rossi X-Ray Timing Explorer (RXTE) spanning 250 days and covering the entire double-peaked eruption that occurred from 1998 September until 1999 May. The spectra are fitted to a model including multicolor blackbody disk and power-law components. The spectra from the first half of the outburst are dominated by the power-law component, whereas the spectra from the second half are dominated by the disk component. The source is observed in the very high and high/soft outburst states of black hole X-ray novae. During the very high state, when the power-law component dominated the spectrum, the inner disk radius is observed to vary by more than an order of magnitude; the radius decreased by a factor of 16 in one day during a 6.8 crab flare. If the larger of these observed radii is taken to be the last stable orbit, then the smaller observed radius would imply that the inner edge of the disk is inside the event horizon! However, we conclude that the apparent variations of the inner disk radius observed during periods of increased power-law emission are probably caused by the failure of the multicolor disk/power-law model; the actual physical radius of the inner disk may remain fairly constant. This interpretation is supported by the fact that the observed inner disk radius remains approximately constant over 120 days in the high state, when the power-law component is weak, even though the disk flux and total flux vary by an order of magnitude. The mass of the black hole inferred by equating the approximately constant inner disk radius observed in the high/soft state with the last stable orbit for a Schwarzschild black hole is M<SUB>BH</SUB>=7.4 M<SUB>solar</SUB>(D/6 kpc)(cosi)<SUP>-1/2</SUP>.

[]

https://arxiv.org/pdf/astro-ph/0005599.pdf

2009PhRvD..80j4039B

An analytic Lifshitz black hole

2009-01-01

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

[]

A Lifshitz point is described by a quantum field theory with anisotropic scale invariance (but not Galilean invariance). In , gravity duals were conjectured for such theories. We construct analytically a black hole that asymptotes to a vacuum Lifshitz solution; this black hole solves the equations of motion of some simple (but somewhat strange) extensions of the models of . We study its thermodynamics and scalar response functions. The scalar wave equation turns out to be exactly solvable. Interestingly, the Green’s functions do not exhibit the ultralocal behavior seen previously in the free Lifshitz scalar theory.

[]

https://arxiv.org/pdf/0909.0263.pdf

2010PhRvD..81h4030J

Uncertainty relation on a world crystal and its applications to micro black holes

2010-01-01

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

[]

We formulate generalized uncertainty relations in a crystal-like universe—a “world crystal”—whose lattice spacing is of the order of Planck length. In the particular case when energies lie near the border of the Brillouin zone, i.e., for Planckian energies, the uncertainty relation for position and momenta does not pose any lower bound on involved uncertainties. We apply our results to micro black holes physics, where we derive a new mass-temperature relation for Schwarzschild micro black holes. In contrast to standard results based on Heisenberg and stringy uncertainty relations, our mass-temperature formula predicts both a finite Hawking’s temperature and a zero rest-mass remnant at the end of the micro black hole evaporation. We also briefly mention some connections of the world-crystal paradigm with ’t Hooft’s quantization and double special relativity.

[]

https://arxiv.org/pdf/0912.2253.pdf

1997NuPhB.488..236B

Classical and quantum N = 2 supersymmetric black holes

1997-01-01

['-']

[]

We use heterotic/type-II prepotentials to study quantum/classical black holes with half the N = 2, D = 4 supersymmetries unbroken. We show that, in the case of heterotic string compactifications, the perturbatively corrected entropy formula is given by the tree-level entropy formula with the tree-level coupling constant replaced by the perturbative coupling constant. In the case of type-II compactifications, we display a new entropy/area formula associated with axion-free black-hole solutions, which depends on the electric and magnetic charges as well as on certain topological data of Calabi-Yau three-folds, namely the intersection numbers, the second Chern class and the Euler number of the three-fold. We show that, for both heterotic and type-II theories, there is the possibility to relax the usual requirement of the non-vanishing of some of the charges and still have a finite entropy.

[]

https://arxiv.org/pdf/hep-th/9610105.pdf

2010ApJ...708..427L

Type 2 Active Galactic Nuclei with Double-Peaked [O III] Lines: Narrow-Line Region Kinematics or Merging Supermassive Black Hole Pairs?

2010-01-01

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

[]

We present a sample of 167 type 2 active galactic nuclei (AGNs) with double-peaked [O III] λλ4959,5007 narrow emission lines, selected from the Seventh Data Release of the Sloan Digital Sky Survey. The double-peaked profiles can be well modeled by two velocity components, blueshifted and redshifted from the systemic velocity. Half of these objects have a more prominent redshifted component. In cases where the Hβ emission line is strong, it also shows two velocity components whose line-of-sight (LOS) velocity offsets are consistent with those of [O III]. The relative LOS velocity offset between the two components is typically a few hundred km s<SUP>-1</SUP>, larger by a factor of ~1.5 than the line full width at half maximum of each component. The offset correlates with the host stellar velocity dispersion σ<SUB>*</SUB>. The host galaxies of this sample show systematically larger σ<SUB>*</SUB>, stellar masses, and concentrations, and older luminosity-weighted mean stellar ages than a regular type 2 AGN sample matched in redshift, [O III] λ5007 equivalent width, and luminosity; they show no significant difference in radio properties. These double-peaked features could be due to narrow-line region kinematics, or binary black holes. The statistical properties do not show strong preference for or against either scenario, and spatially resolved optical imaging, spectroscopy, radio or X-ray follow-up are needed to draw firm conclusions.

[]

https://arxiv.org/pdf/0908.2426.pdf

2001PhRvD..63f4015C

Charged brane-world black holes

2001-01-01

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

[]

We study charged brane-world black holes in the model of Randall and Sundrum in which our universe is viewed as a domain wall in asymptotically anti-de Sitter space. Such black holes can carry two types of ``charge,'' one arising from the bulk Weyl tensor and one from a gauge field trapped on the wall. We use a combination of analytical and numerical techniques to study how these black holes behave in the bulk. It has been shown that a Reissner-Nordström geometry is induced on the wall when only Weyl charge is present. However, we show that such solutions exhibit pathological features in the bulk. For more general charged black holes, our results suggest that the extent of the horizon in the fifth dimension is usually less than for an uncharged black hole that has the same mass or the same horizon radius on the wall.

[]

https://arxiv.org/pdf/hep-th/0008177.pdf

2015MNRAS.447.2059M

Geometrical constraints on the origin of timing signals from black holes

2015-01-01

['stars binaries close', 'stars black holes', '-', 'stars low mass brown dwarfs', 'stars oscillations', 'astronomy x rays', '-']

[]

We present a systematic study of the orbital inclination effects on black hole transients fast time-variability properties. We have considered all the black hole binaries that have been densely monitored by the Rossi X-ray Timing Explorer satellite. We find that the amplitude of low-frequency quasi-periodic oscillations (QPOs) depends on the orbital inclination. type-C QPOs are stronger for nearly edge-on systems (high inclination), while type-B QPOs are stronger when the accretion disc is closer to face-on (low inclination). Our results also suggest that the noise associated with type-C QPOs is consistent with being stronger for low-inclination sources, while the noise associated with type-B QPOs seems inclination independent. These results are consistent with a geometric origin of the type-C QPOs - for instance arising from relativistic precession of the inner flow within a truncated disc - while the noise would correspond to intrinsic brightness variability from mass accretion rate fluctuations in the accretion flow. The opposite behaviour of type-B QPOs - stronger in low-inclinations sources - supports the hypothesis that type-B QPOs are related to the jet, the power of which is the most obvious measurable parameter expected to be stronger in nearly face-on sources.

[]

https://arxiv.org/pdf/1404.7293.pdf

2020PhRvD.101b4056K

Including higher order multipoles in gravitational-wave models for precessing binary black holes

2020-01-01

['-', '-']

[]

Estimates of the source parameters of gravitational-wave (GW) events produced by compact binary mergers rely on theoretical models for the GW signal. We present the first frequency-domain model for the inspiral, merger, and ringdown of the GW signal from precessing binary black hole systems that also includes multipoles beyond the leading-order quadrupole. Our model, PhenomPv3HM, is a combination of the higher-multipole nonprecessing model PhenomHM and the spin-precessing model PhenomPv3 that includes two-spin precession via a dynamical rotation of the GW multipoles. We validate the new model by comparing to a large set of precessing numerical-relativity simulations and find excellent agreement across the majority of the parameter space they cover. For mass ratios &lt;5 the mismatch improves, on average, from ∼6 % to ∼2 % compared to PhenomPv3 when we include higher multipoles in the model. However, we find mismatches ∼8 % for a mass-ratio-6 and highly spinning simulation. We quantify the statistical uncertainty in the recovery of binary parameters by applying standard Bayesian parameter estimation methods to simulated signals. We find that, while the primary black hole spin parameters should be measurable even at moderate signal-to-noise ratios (SNRs) ∼30 , the secondary spin requires much larger SNRs ∼200 . We also quantify the systematic uncertainty expected by recovering our simulated signals with different waveform models in which various physical effects—such as the inclusion of higher modes and/or precession—are omitted and find that even in the low-SNR case (∼17 ) the recovered parameters can be biased. Finally, as a first application of the new model we analyze the binary black hole event GW170729. We find larger values for the primary black hole mass of 58.25<SUB>-12.53</SUB><SUP>+11.73</SUP> M<SUB>⊙</SUB> (90% credible interval). The lower limit (∼46 M<SUB>⊙</SUB> ) is comparable to the proposed maximum black hole mass predicted by different stellar evolution models due to the pulsation pair-instability supernova (PPISN) mechanism. If we assume that the primary black hole in GW170729 formed through a PPISN, then out of the four PPISN models we consider only the model of Woosley [1] is consistent with our mass measurements at the 90% confidence level.

[]

https://arxiv.org/pdf/1911.06050.pdf

2017PhRvD..96b4002S

Distinguishing boson stars from black holes and neutron stars from tidal interactions in inspiraling binary systems

2017-01-01

['-']

[]

Binary systems containing boson stars—self-gravitating configurations of a complex scalar field—can potentially mimic black holes or neutron stars as gravitational-wave sources. We investigate the extent to which tidal effects in the gravitational-wave signal can be used to discriminate between these standard sources and boson stars. We consider spherically symmetric boson stars within two classes of scalar self-interactions: an effective-field-theoretically motivated quartic potential and a solitonic potential constructed to produce very compact stars. We compute the tidal deformability parameter characterizing the dominant tidal imprint in the gravitational-wave signals for a large span of the parameter space of each boson star model, covering the entire space in the quartic case, and an extensive portion of interest in the solitonic case. We find that the tidal deformability for boson stars with a quartic self-interaction is bounded below by Λ<SUB>min</SUB>≈280 and for those with a solitonic interaction by Λ<SUB>min</SUB>≈1.3 . We summarize our results as ready-to-use fits for practical applications. Employing a Fisher matrix analysis, we estimate the precision with which Advanced LIGO and third-generation detectors can measure these tidal parameters using the inspiral portion of the signal. We discuss a novel strategy to improve the distinguishability between black holes/neutrons stars and boson stars by combining tidal deformability measurements of each compact object in a binary system, thereby eliminating the scaling ambiguities in each boson star model. Our analysis shows that current-generation detectors can potentially distinguish boson stars with quartic potentials from black holes, as well as from neutron-star binaries if they have either a large total mass or a large (asymmetric) mass ratio. Discriminating solitonic boson stars from black holes using only tidal effects during the inspiral will be difficult with Advanced LIGO, but third-generation detectors should be able to distinguish between binary black holes and these binary boson stars.

[]

https://arxiv.org/pdf/1704.08651.pdf

2019JHEP...08..001H

Dark radiation and superheavy dark matter from black hole domination

2019-01-01

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

[]

If even a relatively small number of black holes were created in the early universe, they will constitute an increasingly large fraction of the total energy density as space expands. It is thus well-motivated to consider scenarios in which the early universe included an era in which primordial black holes dominated the total energy density. Within this context, we consider Hawking radiation as a mechanism to produce both dark radiation and dark matter. If the early universe included a black hole dominated era, we find that Hawking radiation will produce dark radiation at a level Δ N <SUB>eff</SUB> ∼ 0 .03 - 0 .2 for each light and decoupled species of spin 0, 1/2, or 1. This range is well suited to relax the tension between late and early-time Hubble determinations, and is within the reach of upcoming CMB experiments. The dark matter could also originate as Hawking radiation in a black hole dominated early universe, although such dark matter candidates must be very heavy ( m <SUB>DM</SUB> ≳ 10<SUP>11</SUP> GeV) if they are to avoid exceeding the measured abundance.

[]

https://arxiv.org/pdf/1905.01301.pdf

2001NuPhB.608..375H

Randall-Sundrum II cosmology, AdS/CFT, and the bulk black hole

2001-01-01

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

[]

We analyse the cosmology of a brane world model where a single brane carrying the standard model fields forms the boundary of a 5-dimensional AdS bulk (the Randall-Sundrum II scenario). We focus on the thermal radiation of bulk gravitons, the formation of the bulk black hole, and the holographic AdS/CFT definition of the RSII theory. Our detailed calculation of bulk radiation reduces previous estimates to a phenomenologically acceptable, although potentially visible level. In late cosmology, in which the Friedmann equation depends linearly on the energy density /ρ, only about 1% of energy density is lost to the black hole or, equivalently, to the `dark radiation' (Ω<SUB>d,N</SUB>~=0.01 at nucleosynthesis). The preceding, unconventional ρ<SUP>2</SUP> period can produce up to 10% dark radiation (Ω<SUB>d,N</SUB>&lt;~0.1). The AdS/CFT correspondence provides an equivalent description of late RSII cosmology. We show how the AdS/CFT formulation can reproduce the ρ<SUP>2</SUP> correction to the standard treatment at low matter density. However, the 4-dimensional effective theory of CFT /+ gravity breaks down due to higher curvature terms for energy densities where ρ<SUP>2</SUP> behaviour in the Friedmann equation is usually predicted. We emphasize that, in going beyond this energy density, the microscopic formulation of the theory becomes essential. For example, the pure AdS<SUB>5</SUB> and string-motivated AdS<SUB>5</SUB>×S<SUP>5</SUP> definitions differ in their cosmological implications.

[]

https://arxiv.org/pdf/hep-ph/0103214.pdf

1993PhRvD..48.3600A

Relating black holes in two and three dimensions

1993-01-01

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

[]

The three-dimensional black hole solutions of Bañados, Teitelboim, and Zanelli (BTZ) are dimensionally reduced in various different ways. Solutions are obtained to the Jackiw-Teitelboim theory of two-dimensional gravity for spinless BTZ black holes, and to a simple extension with a nonzero dilaton potential for black holes of fixed spin. Similar reductions are given for charged black holes. The resulting two-dimensional solutions are themselves black holes, and are appropriate for investigating exact ``S-wave'' scattering in the BTZ metrics. Using a different dimensional reduction to the string-inspired model of two-dimensional gravity, the BTZ solutions are related to the familiar two-dimensional black hole and the linear dilaton vacuum.

[]

https://arxiv.org/pdf/hep-th/9304068.pdf

1999PhRvD..60j4039G

Topological censorship and higher genus black holes

1999-01-01

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

[]

Motivated by recent interest in black holes whose asymptotic geometry approaches that of anti-de Sitter spacetime, we give a proof of topological censorship applicable to spacetimes with such asymptotic behavior. Employing a useful rephrasing of topological censorship as a property of homotopies of arbitrary loops, we then explore the consequences of topological censorship for the horizon topology of black holes. We find that the genera of horizons are controled by the genus of the space at infinity. Our results make it clear that there is no conflict between topological censorship and the nonspherical horizon topologies of locally anti-de Sitter black holes. More specifically, let D be the domain of outer communications of a boundary at infinity ``scri.'' We show that the principle of topological censorship (PTC), which is that every causal curve in D having end points on scri can be deformed to scri, holds under reasonable conditions for timelike scri, as it is known to do for a simply connected null scri. We then show that the PTC implies that the fundamental group of scri maps, via inclusion, onto the fundamental group of D: i.e., every loop in D is homotopic to a loop in scri. We use this to determine the integral homology of preferred spacelike hypersurfaces (Cauchy surfaces or analogues thereof) in the domain of outer communications of any four-dimensional spacetime obeying the PTC. From this, we establish that the sum of the genera of the cross sections in which such a hypersurface meets black hole horizons is bounded above by the genus of the cut of infinity defined by the hypersurface. Our results generalize familiar theorems valid for asymptotically flat spacetimes requiring simple connectivity of the domain of outer communications and spherical topology for stationary and evolving black holes.

[]

https://arxiv.org/pdf/gr-qc/9902061.pdf

2009ApJ...692..917M

Mergers of Stellar-Mass Black Holes in Nuclear Star Clusters

2009-01-01

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

[]

Mergers between stellar-mass black holes (BHs) will be key sources of gravitational radiation for ground-based detectors. However, the rates of these events are highly uncertain, given that such systems are invisible. One formation scenario involves mergers in field binaries, where our lack of complete understanding of common envelopes and the distribution of supernova kicks has led to rate estimates that range over a factor of several hundreds. A different, and highly promising, channel involves multiple encounters of binaries in globular clusters or young star clusters. However, we currently lack solid evidence of BHs in almost all such clusters, and their low escape speeds raise the possibility that most are ejected because of supernova recoil. Here, we propose that a robust environment for mergers could be the nuclear star clusters found in the centers of small galaxies. These clusters have millions of stars, BH relaxation times well under a Hubble time, and escape speeds that are several times those of globulars; hence, they retain most of their BHs. We present simulations of the three-body dynamics of BHs in this environment and estimate that, if most nuclear star clusters do not have supermassive BHs that interfere with the mergers, tens of events per year will be detectable with the advanced Laser Interferometer Gravitational-Wave Observatory.

[]

https://arxiv.org/pdf/0804.2783.pdf

2009ApJ...707..428B

Transport of Large-Scale Poloidal Flux in Black Hole Accretion

2009-01-01

['accretion', 'accretion disks', 'mhd', 'relativity', '-']

[]

We report on a global, three-dimensional GRMHD simulation of an accretion torus embedded in a large-scale vertical magnetic field orbiting a Schwarzschild black hole. This simulation investigates how a large-scale vertical field evolves within a turbulent accretion disk and whether global magnetic field configurations suitable for launching jets and winds can develop. We find that a "coronal mechanism" of magnetic flux motion, which operates largely outside the disk body, dominates global flux evolution. In this mechanism, magnetic stresses driven by orbital shear create large-scale half-loops of magnetic field that stretch radially inward and then reconnect, leading to discontinuous jumps in the location of magnetic flux. In contrast, little or no flux is brought in directly by accretion within the disk itself. The coronal mechanism establishes a dipole magnetic field in the evacuated funnel around the orbital axis with a field intensity regulated by a combination of the magnetic and gas pressures in the inner disk. These results prompt a re-evaluation of previous descriptions of magnetic flux motion associated with accretion. Local pictures are undercut by the intrinsically global character of magnetic flux. Formulations in terms of an "effective viscosity" competing with an "effective resistivity" are undermined by the nonlinearity of the magnetic dynamics and the fact that the same turbulence driving mass motion (traditionally identified as "viscosity") can alter magnetic topology.

[]

https://arxiv.org/pdf/0906.2784.pdf

1996NuPhB.478..181C

Non-extreme black holes from non-extreme intersecting M-branes

1996-01-01

['-']

[]

We present non-extreme generalisations of intersecting p-brane solutions of eleven-dimensional supergravity which upon toroidal compactification reduce to non-extreme static black holes in dimensions D = 4, D = 5 and 6 ⩽ D ⩽ 9, parameterised by four, three and two charges, respectively. The D = 4 black holes are obtained either from a non-extreme configuration of three intersecting five-branes with a boost along the common string or from a non-extreme intersecting system of two two-branes and two five-branes. The D = 5 black holes arise from three intersecting two-branes or from a system of an intersecting two-brane and five-brane with a boost along the common string. The five-brane and two-brane with a boost along one direction reduce to black holes in D = 6 and D = 9, respectively, while a D = 7 black hole can be interpreted in terms of a non-extreme configuration of two intersecting two-branes. We discuss the expressions for the corresponding masses and entropies.

[]

https://arxiv.org/pdf/hep-th/9606033.pdf

2007PhRvD..76b4005V

Observation of incipient black holes and the information loss problem

2007-01-01

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

[]

We study the formation of black holes by spherical domain wall collapse as seen by an asymptotic observer, using the functional Schrödinger formalism. To explore what signals such observers will see, we study radiation of a scalar quantum field in the collapsing domain wall background. The total energy flux radiated diverges when backreaction of the radiation on the collapsing wall is ignored, and the domain wall is seen by the asymptotic observer to evaporate by nonthermal “pre-Hawking radiation” during the collapse process. Evaporation by pre-Hawking radiation implies that an asymptotic observer can never lose objects down a black hole. Together with the nonthermal nature of the radiation, this may resolve the black hole information loss problem.

[]

https://arxiv.org/pdf/gr-qc/0609024.pdf

2009arXiv0907.1190B

Better Late than Never: Information Retrieval from Black Holes

2009-01-01

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

[]

We show that, in order to preserve the equivalence principle until late times in unitarily evaporating black holes, the thermodynamic entropy of a black hole must be primarily entropy of entanglement across the event horizon. For such black holes, we show that the information entering a black hole becomes encoded in correlations within a tripartite quantum state, the quantum analogue of a one-time pad, and is only decoded into the outgoing radiation very late in the evaporation. This behavior generically describes the unitary evaporation of highly entangled black holes and requires no specially designed evolution. Our work suggests the existence of a matter-field sum rule for any fundamental theory.

[]

https://arxiv.org/pdf/0907.1190.pdf

2011PhRvD..83j4027V

Bumpy black holes in alternative theories of gravity

2011-01-01

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

[]

We generalize the bumpy black hole framework to allow for alternative theory deformations. We construct two model-independent parametric deviations from the Kerr metric: one built from a generalization of the quasi-Kerr and bumpy metrics and one built directly from perturbations of the Kerr spacetime in Lewis-Papapetrou form. We find the conditions that these “bumps” must satisfy for there to exist an approximate second-order Killing tensor so that the perturbed spacetime still possesses three constants of the motion (a deformed energy, angular momentum and Carter constant) and the geodesic equations can be written in first-order form. We map these parametrized metrics to each other via a diffeomorphism and to known analytical black hole solutions in alternative theories of gravity. The parametrized metrics presented here serve as frameworks for the systematic calculation of extreme mass-ratio inspiral waveforms in parametrized non-general relativity theories and the investigation of the accuracy to which space-borne gravitational wave detectors can constrain such deviations.

[]

https://arxiv.org/pdf/1102.3706.pdf

2010ApJ...714..713S

The NGC 404 Nucleus: Star Cluster and Possible Intermediate-mass Black Hole

2010-01-01

['galaxies elliptical lenticular;cd', 'cd', 'galaxies formation', 'galaxies', 'galaxies kinematics and dynamics', 'galaxies nuclei', 'galaxies structure', '-', '-']

[]

We examine the nuclear morphology, kinematics, and stellar populations in nearby S0 galaxy NGC 404 using a combination of adaptive optics assisted near-IR integral-field spectroscopy, optical spectroscopy, and Hubble Space Telescope imaging. These observations enable study of the NGC 404 nucleus at a level of detail possible only in the nearest galaxies. The surface brightness profile suggests the presence of three components: a bulge, a nuclear star cluster (NSC), and a central light excess within the cluster at radii &lt; 3 pc. These components have distinct kinematics with modest rotation seen in the NSC and counter-rotation seen in the central excess. Molecular hydrogen emission traces a disk with rotation nearly orthogonal to that of the stars. The stellar populations of the three components are also distinct, with half of the mass of the NSC having ages of ~1 Gyr (perhaps resulting from a galaxy merger), while the bulge is dominated by much older stars. Dynamical modeling of the stellar kinematics gives a total NSC mass of 1.1 × 10<SUP>7</SUP> M <SUB>sun</SUB>. Dynamical detection of a possible intermediate-mass black hole (BH) is hindered by uncertainties in the central stellar mass profile. Assuming a constant mass-to-light ratio, the stellar dynamical modeling suggests a BH mass of &lt;1 × 10<SUP>5</SUP> M <SUB>sun</SUB>, while the molecular hydrogen gas kinematics are best fitted by a BH with a mass of 4.5<SUP>+3.5</SUP> <SUB>-2.0</SUB> × 10<SUP>5</SUP> M <SUB>sun</SUB>. Unresolved and possibly variable dust emission in the near-infrared and active galactic nucleus-like molecular hydrogen emission-line ratios do suggest the presence of an accreting BH in this nearby LINER galaxy.

[]

https://arxiv.org/pdf/1003.0680.pdf

2011PhRvD..83d4045P

High accuracy binary black hole simulations with an extended wave zone

2011-01-01

['-', '-', '-', '-', 'methods numerical', 'waves', 'waves', '-', '-']

[]

We present results from a new code for binary black hole evolutions using the moving-puncture approach, implementing finite differences in generalized coordinates, and allowing the spacetime to be covered with multiple communicating nonsingular coordinate patches. Here we consider a regular Cartesian near-zone, with adapted spherical grids covering the wave zone. The efficiencies resulting from the use of adapted coordinates allow us to maintain sufficient grid resolution to an artificial outer boundary location which is causally disconnected from the measurement. For the well-studied test case of the inspiral of an equal-mass nonspinning binary (evolved for more than 8 orbits before merger), we determine the phase and amplitude to numerical accuracies better than 0.010% and 0.090% during inspiral, respectively, and 0.003% and 0.153% during merger. The waveforms, including the resolved higher harmonics, are convergent and can be consistently extrapolated to r→∞ throughout the simulation, including the merger and ringdown. Ringdown frequencies for these modes (to (ℓ,m)=(6,6)) match perturbative calculations to within 0.01%, providing a strong confirmation that the remnant settles to a Kerr black hole with irreducible mass M<SUB>irr</SUB>=0.884355±20×10<SUP>-6</SUP> and spin S<SUB>f</SUB>/M<SUB>f</SUB><SUP>2</SUP>=0.686923±10×10<SUP>-6</SUP>.

[]

https://arxiv.org/pdf/0910.3803.pdf

2013MNRAS.432..530R

Radiative efficiency, variability and Bondi accretion on to massive black holes: the transition from radio AGN to quasars in brightest cluster galaxies

2013-01-01

['accretion', 'accretion disks', 'galaxies active', 'galaxies jets', 'astronomy x rays', '-']

[]

We examine unresolved nuclear X-ray sources in 57 brightest cluster galaxies to study the relationship between nuclear X-ray emission and accretion on to supermassive black holes. The majority of the clusters in our sample have prominent X-ray cavities embedded in the surrounding hot atmospheres, which we use to estimate mean jet power and average accretion rate on to the supermassive black holes over the past several hundred Myr. We find that roughly half of the sample have detectable nuclear X-ray emission. The nuclear X-ray luminosity is correlated with average accretion rate determined using X-ray cavities, which is consistent with the hypothesis that nuclear X-ray emission traces ongoing accretion. The results imply that jets in systems that have experienced recent active galactic nucleus (AGN) outbursts, in the last ∼10<SUP>7</SUP> yr, are `on' at least half of the time. Nuclear X-ray sources become more luminous with respect to the mechanical jet power as the mean accretion rate rises. We show that nuclear radiation exceeds the jet power when the mean accretion rate rises above a few per cent of the Eddington rate, or a power output of {∼ }10^{45} {erg s^{-1}}, where the AGN apparently transitions to a quasar. The nuclear X-ray emission from three objects (A2052, Hydra A, M84) varies by factors of 2-10 on time-scales of 6 months to 10 years. If variability at this level is a common phenomenon, it can account for much of the scatter in the relationship between mean accretion rate and nuclear X-ray luminosity. We find no significant change in the spectral energy distribution as a function of luminosity in the variable objects. The nuclear X-ray luminosity is consistent with emission from either a jet, an advection-dominated accretion flow, or a combination of the two, although other origins are possible. We also consider the longstanding problem of whether jets are powered by the accretion of cold circumnuclear gas or nearly spherical inflows of hot keV gas. For a subset of 13 nearby systems in our sample, we re-examine the relationship between the jet power and the Bondi accretion rate. The results indicate weaker evidence for a trend between Bondi accretion and jet power, due to uncertainties in the cavity volumes and gas densities at the Bondi radius. We suggest that cold gas fuelling could be a likely source of accretion power in these objects; however, we cannot rule out Bondi accretion, which could play a significant role in low-power jets.

[]

https://arxiv.org/pdf/1211.5604.pdf

2015MNRAS.454.1848R

Electron thermodynamics in GRMHD simulations of low-luminosity black hole accretion

2015-01-01

['mhd', 'stars black holes', 'galaxy center', 'galaxies jets', 'galaxies nuclei', '-']

[]

Simple assumptions made regarding electron thermodynamics often limit the extent to which general relativistic magnetohydrodynamic (GRMHD) simulations can be applied to observations of low-luminosity accreting black holes. We present, implement, and test a model that self-consistently evolves an entropy equation for the electrons and takes into account the effects of spatially varying electron heating and relativistic anisotropic thermal conduction along magnetic field lines. We neglect the backreaction of electron pressure on the dynamics of the accretion flow. Our model is appropriate for systems accreting at ≪10<SUP>-5</SUP> of the Eddington accretion rate, so radiative cooling by electrons can be neglected. It can be extended to higher accretion rates in the future by including electron cooling and proton-electron Coulomb collisions. We present a suite of tests showing that our method recovers the correct solution for electron heating under a range of circumstances, including strong shocks and driven turbulence. Our initial applications to axisymmetric simulations of accreting black holes show that (1) physically motivated electron heating rates that depend on the local magnetic field strength yield electron temperature distributions significantly different from the constant electron-to-proton temperature ratios assumed in previous work, with higher electron temperatures concentrated in the coronal region between the disc and the jet; (2) electron thermal conduction significantly modifies the electron temperature in the inner regions of black hole accretion flows if the effective electron mean free path is larger than the local scaleheight of the disc (at least for the initial conditions and magnetic field configurations we study). The methods developed in this work are important for producing more realistic predictions for the emission from accreting black holes such as Sagittarius A* and M87; these applications will be explored in future work.

[]

https://arxiv.org/pdf/1509.04717.pdf