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2005NuPhB.715..304A

Black holes, q-deformed 2d Yang Mills, and non-perturbative topological strings

2005-01-01

['-']

[]

We count the number of bound states of BPS black holes on local Calabi-Yau three-folds involving a Riemann surface of genus g. We show that the corresponding gauge theory on the brane reduces to a q-deformed Yang-Mills theory on the Riemann surface. Following the recent connection between the black hole entropy and the topological string partition function, we find that for a large black hole charge N, up to corrections of O(e), Z is given as a sum of a square of chiral blocks, each of which corresponds to a specific D-brane amplitude. The leading chiral block, the vacuum block, corresponds to the closed topological string amplitudes. The subleading chiral blocks involve topological string amplitudes with D-brane insertions at (2g-2) points on the Riemann surface analogous to the Ω points in the large N 2d Yang-Mills theory. The finite N amplitude provides a non-perturbative definition of topological strings in these backgrounds. This also leads to a novel non-perturbative formulation of c=1 non-critical string at the self-dual radius.

[]

https://arxiv.org/pdf/hep-th/0411280.pdf

1995PhRvD..52.5816B

Global charges in Chern-Simons theory and the 2+1 black hole

1995-01-01

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

[]

We use the Regge-Teitelboim method to treat surface integrals in gauge theories to find global charges in Chern-Simons theory. We derive the affine and Virasoro generators as global charges associated with symmetries of the boundary. The role of boundary conditions is clarified. We prove that for diffeomorphisms that do not preserve the boundary there is a classical contribution to the central charge in the Virasoro algebra. The example of anti-de Sitter 2+1 gravity is considered in detail.

[]

https://arxiv.org/pdf/hep-th/9405171.pdf

2007PhRvD..76j4015S

Binary black-hole evolutions of excision and puncture data

2007-01-01

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

[]

We present a new numerical code developed for the evolution of binary black-hole spacetimes using different initial data and evolution techniques. The code is demonstrated to produce state-of-the-art simulations of orbiting and inspiralling black-hole binaries with convergent waveforms. We also present the first detailed study of the dependence of gravitational waveforms resulting from three-dimensional evolutions of different types of initial data. For this purpose we compare the waveforms generated by head-on collisions of superposed Kerr-Schild, Misner, and Brill-Lindquist data over a wide range of initial separations.

[]

https://arxiv.org/pdf/gr-qc/0606079.pdf

2004JHEP...03..064E

Rotating circular strings, and infinite non-uniqueness of black rings

2004-01-01

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

[]

We present new self-gravitating solutions in five dimensions that describe circular strings, i.e. rings, electrically coupled to a two-form potential (as e.g. fundamental strings do), or to a dual magnetic one-form. The rings are prevented from collapsing by rotation, and they create a field analogous to a dipole, with no net charge measured at infinity. They can have a regular horizon, and we show that this implies the existence of an infinite number of black rings, labeled by a continuous parameter, with the same mass and angular momentum as neutral black rings and black holes. We also discuss the solution for a rotating loop of fundamental string. We show how more general rings arise from intersections of branes with a regular horizon (even at extremality), closely related to the configurations that yield the four-dimensional black hole with four charges. We reproduce the Bekenstein-Hawking entropy of a large extremal ring through a microscopic calculation. Finally, we discuss some qualitative ideas for a microscopic understanding of neutral and dipole black rings.

[]

https://arxiv.org/pdf/hep-th/0402149.pdf

2010MNRAS.406.1425F

No evidence for black hole spin powering of jets in X-ray binaries

2010-01-01

['ism jets and outflows', '-', '-', '-', '-']

[]

In this paper, we consider the reported measurements of black hole spin for black hole X-ray binaries and compare them against the measurements of jet power and speed across all accretion states in these systems. We find no evidence for any correlation between the properties of the jets and the reported spin measurements. These constraints are strongest in the hard X-ray state, which is associated with a continuous powerful jet. We are led to conclude that one or more of the following is correct: (i) the calculated jet power and speed measurements are wrong, (ii) the reported spin measurements are wrong and (iii) there is no strong dependence of the jet properties on the black hole spin. In addition to this lack of observational evidence for a relation between the black hole spin and jet properties in stellar mass black holes, we highlight the fact that there appear to be at least three different ways in which the jet power and/or radiative efficiency from a black hole X-ray binary may vary, two of which are certainly independent of spin because they occur in the same source on relatively short time-scales and the third which does not correlate with any reported measurements of black hole spin. We briefly discuss how these findings may impact upon interpretations of populations of active galactic nuclei in the context of black hole spin and merger history.

[]

https://arxiv.org/pdf/1003.5516.pdf

1999PhRvD..59l4022C

Second order gauge invariant gravitational perturbations of a Kerr black hole

1999-01-01

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

[]

We investigate higher than the first order gravitational perturbations in the Newman-Penrose formalism. Equations for the Weyl scalar ψ<SUB>4</SUB>, representing outgoing gravitational radiation, can be uncoupled into a single wave equation to any perturbative order. For second order perturbations about a Kerr black hole, we prove the existence of a first and second order gauge (coordinates) and tetrad invariant waveform, ψ<SUB>I</SUB>, by explicit construction. This waveform is formed by the second order piece of ψ<SUB>4</SUB> plus a term, quadratic in first order perturbations, chosen to make ψ<SUB>I</SUB> totally invariant and to have the appropriate behavior in an asymptotically flat gauge. ψ<SUB>I</SUB> satisfies a single wave equation of the form Tψ<SUB>I</SUB>=S, where T is the same wave operator as for first order perturbations and S is a source term build up out of (known to this level) first order perturbations. We discuss the issues of imposition of initial data to this equation, computation of the energy and momentum radiated and wave extraction for direct comparison with full numerical approaches to solve Einstein equations.

[]

https://arxiv.org/pdf/gr-qc/9811019.pdf

2019EPJC...79..246B

Clusters of Primordial Black Holes

2019-01-01

['-']

[]

The Primordial Black Holes (PBHs) are a well-established probe for new physics in the very early Universe. We discuss here the possibility of PBH agglomeration into clusters that may have several prominent observable features. The clusters can form due to closed domain walls appearance in the natural and hybrid inflation models whose subsequent evolution leads to PBH formation. The dynamical evolution of such clusters discussed here is of crucial importance. Such a model inherits all the advantages of uniformly distributed PBHs, like possible explanation of supermassive black holes existence (origin of the early quasars), the binary black hole mergers registered by LIGO/Virgo through gravitational waves, which could provide ways to test the model in future, the contribution to reionization of the Universe. If PBHs form clusters, they could alleviate or completely avoid existing constraints on the abundance of uniformly distributed to PBH, thus allowing PBH to be a viable dark matter candidate. Most of the existing constraints on uniform PBH density should be re-considered to the case of PBH clustering. Furthermore, unidentified cosmic gamma-ray point-like sources could be (partially) accounted. We conclude that models leading to PBH clustering are favored compared to models predicting the uniform distribution of PBHs.

[]

https://arxiv.org/pdf/1807.06590.pdf

2019MNRAS.486.5008A

Black hole growth through hierarchical black hole mergers in dense star clusters: implications for gravitational wave detections

2019-01-01

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

[]

In a star cluster with a sufficiently large escape velocity, black holes (BHs) that are produced by BH mergers can be retained, dynamically form new BH binaries, and merge again. This process can repeat several times and lead to significant mass growth. In this paper, we calculate the mass of the largest BH that can form through repeated BH mergers and determine how its value depends on the physical properties of the host cluster. We adopt an analytical model in which the energy generated by the black hole binaries in the cluster core is assumed to be regulated by the process of two-body relaxation in the bulk of the system. This principle is used to compute the hardening rate of the binaries and to relate this to the time-dependent global properties of the parent cluster. We demonstrate that in clusters with initial escape velocity {≳ } 300 {km s}^{-1} in the core and density {≳ } 10^5 M_⊙ pc^{-3}, repeated mergers lead to the formation of BHs in the mass range 100-10^5 M_⊙, populating any upper mass gap created by pair-instability supernovae. This result is independent of cluster metallicity and the initial BH spin distribution. We show that about 10{{ per cent}} of the present-day nuclear star clusters meet these extreme conditions, and estimate that BH binary mergers with total mass {≳ } 100 M _⊙ should be produced in these systems at a maximum rate {≈ } 0.05 Gpc^{-3} yr^{-1}, corresponding to one detectable event every few years with Advanced LIGO/Virgo at design sensitivity.

[]

https://arxiv.org/pdf/1811.03640.pdf

2014ApJ...794..104S

Linking the Spin Evolution of Massive Black Holes to Galaxy Kinematics

2014-01-01

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

[]

We present the results of a semianalytical model that evolves the masses and spins of massive black holes together with the properties of their host galaxies across the cosmic history. As a consistency check, our model broadly reproduces a number of observations, e.g., the cosmic star formation history; the black hole mass, luminosity, and galaxy mass functions at low redshift; the black hole-bulge mass relation; and the morphological distribution at low redshift. For the first time in a semianalytical investigation, we relax the simplifying assumptions of perfect coherency or perfect isotropy of the gas fueling the black holes. The dynamics of gas is instead linked to the morphological properties of the host galaxies, resulting in different spin distributions for black holes hosted in different galaxy types. We compare our results with the observed sample of spin measurements obtained through broad Kα iron line fitting. The observational data disfavor both accretion along a fixed direction and isotropic fueling. Conversely, when the properties of the accretion flow are anchored to the kinematics of the host galaxy, we obtain a good match between theoretical expectations and observations. A mixture of coherent accretion and phases of activity in which the gas dynamics is similar to that of the stars in bulges (i.e., with a significant velocity dispersion superimposed to a net rotation) best describes the data, adding further evidence in support of the coevolution of massive black holes and their hosts.

[]

https://arxiv.org/pdf/1402.7088.pdf

2016PhLB..756..350K

Detection of gravitational waves from black holes: Is there a window for alternative theories?

2016-01-01

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

[]

Recently the LIGO and VIRGO Collaborations reported the observation of gravitational-wave signal corresponding to the inspiral and merger of two black holes, resulting into formation of the final black hole. It was shown that the observations are consistent with the Einstein theory of gravity with high accuracy, limited mainly by the statistical error. Angular momentum and mass of the final black hole were determined with rather large allowance of tens of percents. Here we shall show that this indeterminacy in the range of the black-hole parameters allows for some non-negligible deformations of the Kerr spacetime leading to the same frequencies of the black-hole ringing. This means that at the current precision of the experiment there remains some possibility for alternative theories of gravity.

[]

https://arxiv.org/pdf/1602.04738.pdf

2018JCAP...07..007D

Primordial black holes and second order gravitational waves from ultra-slow-roll inflation

2018-01-01

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

[]

The next generation of space-borne gravitational wave detectors may detect gravitational waves from extreme mass-ratio inspirals with primordial black holes. To produce primordial black holes which contribute a non-negligible abundance of dark matter and are consistent with the observations, a large enhancement in the primordial curvature power spectrum is needed. For a single field slow-roll inflation, the enhancement requires a very flat potential for the inflaton, and this will increase the number of e-folds. To avoid the problem, an ultra-slow-roll inflation at the near inflection point is required. We elaborate the conditions to successfully produce primordial black hole dark matter from single field inflation and propose a toy model with polynomial potential to realize the big enhancement of the curvature power spectrum at small scales while maintaining the consistency with the observations at large scales. The power spectrum for the second order gravitational waves generated by the large density perturbations at small scales is consistent with the current pulsar timing array observations.

[]

https://arxiv.org/pdf/1707.09578.pdf

2020PhRvD.101j4018W

Extended thermodynamics and microstructures of four-dimensional charged Gauss-Bonnet black hole in AdS space

2020-01-01

['-', '-']

[]

The discovery of new four-dimensional black hole solutions presents a new approach to understand the Gauss-Bonnet gravity in low dimensions. In this paper, we test the Gauss-Bonnet gravity by studying the phase transition and microstructures for the four-dimensional charged anti-de Sitter black hole. In the extended phase space, where the cosmological constant and the Gauss-Bonnet coupling parameter are treated as thermodynamic variables, we find that the thermodynamic first law and the corresponding Smarr formula are satisfied. Both in the canonical ensemble and grand canonical ensemble, we observe the small-large black hole phase transition, which is similar to the case of the van der Walls fluid. This phase transition can also appear in the neutral black hole system. Furthermore, we construct the Ruppeiner geometry, and find that besides the attractive interaction, the repulsive interaction can also dominate among the microstructures for the small black hole with high temperature in a charged or neutral black hole system. This is quite different from the five-dimensional neutral black hole, for which only dominant attractive interaction can be found. The critical behaviors of the normalized scalar curvature are also examined. These results will shed new light into the characteristic property of four-dimensional Gauss-Bonnet gravity.

[]

https://arxiv.org/pdf/2003.14275.pdf

1998gr.qc.....8028B

Black Holes: Classical Properties, Thermodynamics and Heuristic Quantization

1998-01-01

['-']

[]

I discuss the no hair principle, the recently found hairy solutions, generic properties of nonvacuum spherical static black holes, and the new no scalar hair theorems. I go into the generic phenomenon of superradiance, first uniform linear motion superradiance, then Kerr black hole superradiance, and finally general rotational superradiance and its possible applications in the laboratory. I show that the horizon area of a nearly stationary black hole can be regarded as an adiabatic invariant. This invariance suggests that quantum horizon area is quantized in multiples of a basic unit. Consideration of the quantum version of the Christodoulou reversible processes provides support for this idea. Horizon area quantization dictates a definite discrete black hole mass spectrum, so that Hawking's semiclassical spectrum is predicted to be replaced by a spectrum of nearly uniformly spaced lines whose envelope is roughly Planckian. Line natural broadening seems not enough to wash out the lines. To check on the possibility of line splitting, I present a simple algebra involving, among other operators, the black hole observables. Under simple assumptions it also leads to the uniformly spaced area spectrum.

[]

https://arxiv.org/pdf/gr-qc/9808028.pdf

2002IJMPA..17.4809N

Friedmann-Robertson Brane Cosmological Equations from the Five-Dimensional BULk (A)dS Black Hole

2002-01-01

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

[]

In the first part of this work we review the equations of motion for the brane presented in Friedmann-Robertson-Walker (FRW) form, when the bulk is five-dimensional (A)dS Black Hole. The spacelike (timelike) FRW brane equations are considered from the point of view of their representation in the form similar to two-dimensional CFT entropy, the so-called Cardy-Verlinde (CV) formula. The following five-dimensional gravities are reviewed: Einstein, Einstein-Maxwell and Einstein with brane quantum corrections. The second part of the work is devoted to the study of FRW brane equations and their representation in CV form, brane induced matter and brane cosmology in Einstein-Gauss-Bonnet (GB) gravity. In particular, we focus on the inflationary brane cosmology. The energy conditions for brane matter are also analyzed. We show that for some values of GB coupling constant (bulk is AdS BH) the brane matter is not CFT. Its energy density and pressure are not always positive. The appearance of logarithmic corrections in brane cosmology is discussed.

[]

https://arxiv.org/pdf/hep-th/0205187.pdf

2017PhRvD..96j4014S

Gedanken experiments to destroy a black hole. II. Kerr-Newman black holes cannot be overcharged or overspun

2017-01-01

['-', '-']

[]

We consider gedanken experiments to destroy an extremal or nearly extremal Kerr-Newman black hole by causing it to absorb matter with sufficient charge and/or angular momentum as compared with energy that it cannot remain a black hole. It was previously shown by one of us that such gedanken experiments cannot succeed for test particle matter entering an extremal Kerr-Newman black hole. We generalize this result here to arbitrary matter entering an extremal Kerr-Newman black hole, provided only that the nonelectromagnetic contribution to the stress-energy tensor of the matter satisfies the null energy condition. We then analyze the gedanken experiments proposed by Hubeny and others to overcharge and/or overspin an initially slightly nonextremal Kerr-Newman black hole. Analysis of such gedanken experiments requires that we calculate all effects on the final mass of the black hole that are second-order in the charge and angular momentum carried into the black hole, including all self-force effects. We obtain a general formula for the full second order correction to mass, δ<SUP>2</SUP>M , which allows us to prove that no gedanken experiments of the generalized Hubeny type can ever succeed in overcharging and/or overspinning a Kerr-Newman black hole, provided only that the nonelectromagnetic stress-energy tensor satisfies the null energy condition. Our analysis is based upon Lagrangian methods, and our formula for the second-order correction to mass is obtained by generalizing the canonical energy analysis of Hollands and Wald to the Einstein-Maxwell case. Remarkably, we obtain our formula for δ<SUP>2</SUP>M without having to explicitly compute self-force or finite size effects. Indeed, in an appendix, we show explicitly that our formula incorporates both the self-force and finite size effects for the special case of a charged body slowly lowered into an uncharged black hole.

[]

https://arxiv.org/pdf/1707.05862.pdf

1994PhRvD..50.2662D

Pair creation of extremal black holes and Kaluza-Klein monopoles

1994-01-01

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

[]

Classical solutions describing charged dilaton black holes accelerating in a background magnetic field have recently been found. They include the Ernst metric of the Einstein-Maxwell theory as a special case. We study the extremal limit of these solutions in detail, both at the classical and quantum levels. It is shown that near the event horizon the extremal solutions reduce precisely to the static extremal black hole solutions. For a particular value of the dilaton coupling, these extremal black holes are five-dimensional Kaluza-Klein monopoles. The Euclidean sections of these solutions can be interpreted as instantons describing the pair creation of extremal black holes and/or Kaluza-Klein monopoles in a magnetic field. The action of these instantons is calculated and found to agree with the Schwinger result in the weak-field limit. For the Euclidean Ernst solution, the action for the extremal solution differs from that of the previously discussed wormhole instanton by the Bekenstein-Hawking entropy. However, in many cases quantum corrections become large in the vicinity of the black hole, and the precise description of the creation process is unknown.

[]

https://arxiv.org/pdf/hep-th/9312172.pdf

2009PhRvD..80b4036C

Strong field gravitational lensing in the deformed Hořava-Lifshitz black hole

2009-01-01

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

[]

Adopting the strong field limit approach, we studied the properties of strong field gravitational lensing in the deformed Hořava-Lifshitz black hole and obtained the angular position and magnification of the relativistic images. Supposing that the gravitational field of the supermassive central object of the galaxy described by this metric, we estimated the numerical values of the coefficients and observables for gravitational lensing in the strong field limit. Comparing with the Reissner-Nordström black hole, we find that with the increase of parameter α, the angular position θ<SUB>∞</SUB> decreases more slowly and r<SUB>m</SUB> more quickly, but angular separation s increases more rapidly. This may offer a way to distinguish a deformed Hořava-Lifshitz black hole from a Reissner-Nordström black hole by the astronomical instruments in the future.

[]

https://arxiv.org/pdf/0905.2055.pdf

2011ApJ...727L..31S

HST WFC3/IR Observations of Active Galactic Nucleus Host Galaxies at z ~ 2: Supermassive Black Holes Grow in Disk Galaxies

2011-01-01

['galaxies active', 'galaxies photometry', 'galaxies seyfert', '-', '-']

[]

We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5 &lt; z &lt; 3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGNs are X-ray-selected from the Chandra Deep Field South and have typical luminosities of 10<SUP>42</SUP> erg s<SUP>-1</SUP>&lt;L <SUB>X</SUB> &lt; 10<SUP>44</SUP> erg s<SUP>-1</SUP>. Accreting black holes in this luminosity and redshift range account for a substantial fraction of the total space density and black hole mass growth over cosmic time; they thus represent an important mode of black hole growth in the universe. We find that the majority (~80%) of the host galaxies of these AGNs have low Sérsic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z ~ 2 and z ~ 0.05. <P />Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555.

[]

https://arxiv.org/pdf/1012.1855.pdf

1998PhRvD..57.6547C

Topological dilaton black holes

1998-01-01

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

[]

In four-dimensional spacetime, when the two-sphere of black hole event horizons is replaced by a two-dimensional hypersurface with zero or negative constant curvature, the black hole is referred to as a topological black hole. In this paper we present some exact topological black hole solutions in the Einstein-Maxwell dilaton theory with a Liouville-type dilaton potential.

[]

https://arxiv.org/pdf/gr-qc/9708063.pdf

2000gr.qc.....5126A

Quantum Geometry of Isolated Horizons and Black Hole Entropy

2000-01-01

['-', '-']

[]

Using the earlier developed classical Hamiltonian framework as the point of departure, we carry out a non-perturbative quantization of the sector of general relativity, coupled to matter, admitting non-rotating isolated horizons as inner boundaries. The emphasis is on the quantum geometry of the horizon. Polymer excitations of the bulk quantum geometry pierce the horizon endowing it with area. The intrinsic geometry of the horizon is then described by the quantum Chern-Simons theory of a U(1) connection on a punctured 2-sphere, the horizon. Subtle mathematical features of the quantum Chern-Simons theory turn out to be important for the existence of a coherent quantum theory of the horizon geometry. Heuristically, the intrinsic geometry is flat everywhere except at the punctures. The distributional curvature of the U(1) connection at the punctures gives rise to quantized deficit angles which account for the overall curvature. For macroscopic black holes, the logarithm of the number of these horizon microstates is proportional to the area, irrespective of the values of (non-gravitational) charges. Thus, the black hole entropy can be accounted for entirely by the quantum states of the horizon geometry. Our analysis is applicable to all non-rotating black holes, including the astrophysically interesting ones which are very far from extremality. Furthermore, cosmological horizons (to which statistical mechanical considerations are known to apply) are naturally incorporated. An effort has been made to make the paper self-contained by including short reviews of the background material.

[]

https://arxiv.org/pdf/gr-qc/0005126.pdf

2022PhRvD.105h3526F

Searching for a subpopulation of primordial black holes in LIGO-Virgo gravitational-wave data

2022-01-01

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

[]

With several dozen binary black hole events detected by LIGO-Virgo to date and many more expected in the next few years, gravitational-wave astronomy is shifting from individual-event analyses to population studies. Using the GWTC-2 catalog, we perform a hierarchical Bayesian analysis that for the first time combines several state-of-the-art astrophysical formation models with a population of primordial black holes (PBHs) and constrains the fraction of a putative subpopulation of PBHs in the data. We find that this fraction depends significantly on the set of assumed astrophysical models. While a primordial population is statistically favored against certain competitive astrophysical channels, such as globular clusters and nuclear stellar clusters, a dominant contribution from the stable-mass-transfer isolated formation channel drastically reduces the need for PBHs, except for explaining the rate of mass-gap events like GW190521. The tantalizing possibility that black holes formed after inflation are contributing to LIGO-Virgo observations could only be verified by further reducing uncertainties in astrophysical and primordial formation models, and it may ultimately be confirmed by third-generation interferometers.

[]

https://arxiv.org/pdf/2105.03349.pdf

2007PhRvD..76l4002P

Recoil velocities from equal-mass binary black-hole mergers: A systematic investigation of spin-orbit aligned configurations

2007-01-01

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

[]

Binary black-hole systems with spins aligned with the orbital angular momentum are of special interest, as studies indicate that this configuration is preferred in nature due to non-vacuum environmental interactions, as well as post-Newtonian (PN) spin-orbit couplings. If the spins of the two bodies differ, there can be a prominent beaming of the gravitational radiation during the late plunge, causing a recoil of the final merged black hole. In this paper we perform an accurate and systematic study of recoil velocities from a sequence of equal-mass black holes whose spins are aligned with the orbital angular momentum, and whose individual spins range from a=+0.584 to -0.584. In this way we extend and refine the results of a previous study which concentrated on the antialigned portion of this sequence, to arrive at a consistent maximum recoil of 448±5km/s for antialigned models as well as to a phenomenological expression for the recoil velocity as a function of spin ratio. Quite surprisingly, this relation highlights a nonlinear behavior, not predicted by the PN estimates, and can be readily employed in astrophysical studies on the evolution of binary black holes in massive galaxies. An essential result of our analysis, without which no systematic behavior can be found, is the identification of different stages in the waveform, including a transient due to lack of an initial linear momentum in the initial data. Furthermore, by decomposing the recoil computation into coupled modes, we are able to identify a pair of terms which are largely responsible for the kick, indicating that an accurate computation can be obtained from modes up to ℓ=3. Finally, we provide accurate measures of the radiated energy and angular momentum, finding these to increase linearly with the spin ratio, and derive simple expressions for the final spin and the radiated angular momentum which can be easily implemented in N-body simulations of compact stellar systems. Our code is calibrated with strict convergence tests and we verify the correctness of our measurements by using multiple independent methods whenever possible.

[]

https://arxiv.org/pdf/0707.2559.pdf

2010PhRvD..82j4035M

Charged rotating noncommutative black holes

2010-01-01

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

[]

In this paper we complete the program of the noncomutative geometry inspired black holes, providing the richest possible solution, endowed with mass, charge and angular momentum. After providing a prescription for employing the Newman-Janis algorithm in the case of nonvanishing stress tensors, we find regular axisymmetric charged black holes in the presence of a minimal length. We study also the new thermodynamics and we determine the corresponding higher-dimensional solutions. As a conclusion we make some consideration about possible applications.

[]

https://arxiv.org/pdf/1005.5605.pdf

2011MNRAS.416..941S

The spin of the black hole microquasar XTE J1550-564 via the continuum-fitting and Fe-line methods

2011-01-01

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

[]

We measure the spin of XTE J1550-564 using the two leading methods: (i) modelling the thermal continuum spectrum of the accretion disc; and (ii) modelling the broad red wing of the reflection fluorescence Fe Kα line. We find that these two independent measurements of spin are in agreement. For the continuum-fitting analysis, we use a data sample consisting of several dozen Rossi X-ray Timing Explorer spectra, and for the Fe Kα analysis, we use a pair of ASCA spectra from a single epoch. Our spin estimate for the black hole primary using the continuum-fitting method is -0.11 &lt; a<SUB>*</SUB> &lt; 0.71 (90 per cent confidence), with a most likely spin of a<SUB>*</SUB>= 0.34. In obtaining this result, we have thoroughly explored the dependence of the spin value on a wide range of model-dependent systematic errors and observational errors; our precision is limited by uncertainties in the distance and orbital inclination of the system. For the Fe-line method, our estimate of spin is a<SUB>*</SUB>= 0.55<SUP>+0.15</SUP><SUB>- 0.22</SUB>. Combining these results, we conclude that the spin of this black hole is moderate, a<SUB>*</SUB>= 0.49<SUP>+0.13</SUP><SUB>- 0.20</SUB>, which suggests that the jet activity of this microquasar is powered largely by its accretion disc rather than by the spin energy of the black hole.

[]

https://arxiv.org/pdf/1010.1013.pdf

2001ApJ...559L..25W

``Stable'' Quasi-periodic Oscillations and Black Hole Properties from Diskoseismology

2001-01-01

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

[]

We compare our calculations of the frequencies of the fundamental g-, c-, and p-modes of relativistic thin accretion disks with recent observations of high-frequency quasi-periodic oscillations (QPOs) in X-ray binaries with black hole candidates. These classes of modes encompass all adiabatic perturbations of such disks. The frequencies of these modes depend mainly on the mass and angular momentum of the black hole; their weak dependence on disk luminosity is also explicitly indicated. Identifying the recently discovered, relatively stable QPO pairs with the fundamental g- and c-modes provides a determination of the mass and angular momentum of the black hole. For GRO J1655-40, M=5.9+/-1.0 M<SUB>solar</SUB> and J=(0.917+/-0.024)GM<SUP>2</SUP>/c, in agreement with spectroscopic mass determinations. For GRS 1915+105, M=42.4+/-7.0 M<SUB>solar</SUB> and J=(0.926+/-0.020)GM<SUP>2</SUP>/c or (less favored) M=18.2+/-3.1 M<SUB>solar</SUB> and J=(0.701+/-0.043)GM<SUP>2</SUP>/c. We briefly address the issues of the amplitude, frequency width, and energy dependence of these QPOs.

[]

https://arxiv.org/pdf/astro-ph/0107168.pdf

2002ApJ...570L..69M

Evidence of Spin and Energy Extraction in a Galactic Black Hole Candidate: The XMM-Newton/EPIC-pn Spectrum of XTE J1650-500

2002-01-01

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

[]

We observed the Galactic black hole candidate XTE J1650-500 early in its fall of 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn). The observed spectrum is consistent with the source having been in the ``very high'' state. We find a broad, skewed Fe Kα emission line that suggests the primary in this system may be a Kerr black hole and that indicates a steep disk emissivity profile that is hard to explain in terms of a standard accretion disk model. These results are quantitatively and qualitatively similar to those from an XMM-Newton observation of the Seyfert galaxy MCG -6-30-15. The steep emissivity in MCG -6-30-15 may be explained by the extraction and dissipation of rotational energy from a black hole with nearly maximal angular momentum or from material in the plunging region via magnetic connections to the inner accretion disk. If this process is at work in both sources, an exotic but fundamental general relativistic prediction may be confirmed across a factor of 10<SUP>6</SUP> in black hole mass. We discuss these results in terms of the accretion flow geometry in stellar-mass black holes and the variety of enigmatic phenomena often observed in the very high state.

[]

https://arxiv.org/pdf/astro-ph/0202375.pdf

2005APh....23..265K

Primordial structure of massive black hole clusters

2005-01-01

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

[]

We describe a mechanism of the primordial black holes formation that can explain the existence of a population of supermassive black holes in galactic bulges. The mechanism is based on the formation of black holes from closed domain walls. The origin of such domain walls could be a result of the evolution of an effectively massless scalar field during inflation. The initial non-equilibrium distribution of the scalar field imposed by background de Sitter fluctuations gives rise to the spectrum of black holes, which covers a wide range of masses—from superheavy ones down to deeply subsolar. The primordial black holes of smaller masses are concentrated around the most massive ones within a fractal-like cluster.

[]

https://arxiv.org/pdf/astro-ph/0401532.pdf

2013ApJ...773....3C

A Correlation between Star Formation Rate and Average Black Hole Accretion in Star-forming Galaxies

2013-01-01

['galaxies active', 'galaxies evolution', 'galaxies starburst', 'astronomy infrared', 'astronomy x rays', '-', '-']

[]

We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of the star formation rate (SFR) for galaxies in the redshift range 0.25 &lt; z &lt; 0.8. We study a sample of 1767 far-IR-selected star-forming galaxies in the 9 deg<SUP>2</SUP> Boötes multi-wavelength survey field. The SFR is estimated using 250 μm observations from the Herschel Space Observatory, for which the contribution from the active galactic nucleus (AGN) is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M <SUB>⊙</SUB> yr<SUP>-1</SUP>) and the SFR (in M <SUB>⊙</SUB> yr<SUP>-1</SUP>) for galaxies across a wide SFR range 0.85 &lt; log SFR &lt; 2.56: log BHAR = (- 3.72 ± 0.52) + (1.05 ± 0.33)log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.

[]

https://arxiv.org/pdf/1306.1227.pdf

2015PhRvD..92h4005A

Optical properties of black holes in the presence of a plasma: The shadow

2015-01-01

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

[]

We have studied photon motion around axially symmetric rotating Kerr black holes in the presence of a plasma with radial power-law density. It is shown that in the presence of a plasma, the observed shape and size of the shadow changes depending on the (i) plasma parameters, (ii) black hole spin, and (iii) inclination angle between the observer plane and the axis of rotation of the black hole. In order to extract the pure effect of the plasma influence on the black hole image, the particular case of the Schwarzschild black hole has also been investigated and it has been shown that the photon sphere around the spherically symmetric black hole is left unchanged under the plasma influence; however, the Schwarzschild black hole shadow size in the plasma is reduced due to the refraction of the electromagnetic radiation in the plasma environment of the black hole. The study of the energy emission from the black hole in plasma environment shows that in the presence of the plasma the maximal energy emission rate from the black hole decreases.

[]

https://arxiv.org/pdf/1507.08131.pdf

2012PhRvD..86d4011L

AdS and Lifshitz black holes in conformal and Einstein-Weyl gravities

2012-01-01

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

[]

We study black hole solutions in extended gravities with higher-order curvature terms, including conformal and Einstein-Weyl gravities. In addition to the usual anti-de Sitter (AdS) vacuum, the theories admit Lifshitz and Schrödinger vacua. The AdS black hole in conformal gravity contains an additional parameter over and above the mass, which may be interpreted as a massive spin-2 hair. By considering the first law of thermodynamics, we find that it is necessary to introduce an associated additional intensive/extensive pair of thermodynamic quantities. We also obtain new Lifshitz black holes in conformal gravity and study their thermodynamics. We use a numerical approach to demonstrate that AdS black holes beyond the Schwarzschild-AdS solution exist in Einstein-Weyl gravity. We also demonstrate the existence of asymptotically Lifshitz black holes in Einstein-Weyl gravity. The Lifshitz black holes arise at the boundary of the parameter ranges for the AdS black holes. Outside the range, the solutions develop naked singularities. The asymptotically AdS and Lifshitz black holes provide an interesting phase transition, in the corresponding boundary field theory, from a relativistic Lorentzian system to a nonrelativistic Lifshitz system.

[]

https://arxiv.org/pdf/1204.1062.pdf

2013Sci...339...49M

Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes

2013-01-01

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

[]

Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH’s spin magnitude and direction. Although thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various spin vectors and disk thicknesses and with magnetic flux reaching saturation. Our simulations reveal a “magneto-spin alignment” mechanism that causes magnetized disks and jets to align with the BH spin near BHs and to reorient with the outer disk farther away. This mechanism has implications for the evolution of BH mass and spin, BH feedback on host galaxies, and resolved BH images for the accreting BHs in SgrA* and M87.

[]

https://arxiv.org/pdf/1211.3651.pdf

2009MNRAS.400.1911V

Journey to the M<SUB>BH</SUB>-σ relation: the fate of low-mass black holes in the Universe

2009-01-01

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

[]

In this paper, we explore the establishment and evolution of the empirical correlation between black hole mass (M<SUB>BH</SUB>) and velocity dispersion (σ) with redshift. We trace the growth and accretion history of massive black holes (MBHs) starting from high-redshift seeds that are planted via physically motivated prescriptions. Two seeding models are explored in this work: `light seeds', derived from Population III remnants, and `heavy seeds', derived from direct gas collapse. Even though the seeds themselves do not satisfy the M<SUB>BH</SUB>-σ relation initially, we find that the relation can be established and maintained at all times if self-regulating accretion episodes are associated with major mergers. The massive end of the M<SUB>BH</SUB>-σ relation is established early, and lower mass MBHs migrate on to it as hierarchical merging proceeds. How MBHs migrate towards the relation depends critically on the seeding prescription. Light seeds initially lie well below the M<SUB>BH</SUB>-σ relation, and MBHs can grow via steady accretion episodes unhindered by self-regulation. In contrast, for the heavy seeding model, MBHs are initially over-massive compared to the empirical correlation, and the host haloes assemble prior to kick-starting the growth of the MBH. We find that the existence of the M<SUB>BH</SUB>-σ correlation is purely a reflection of the merging hierarchy of massive dark matter haloes. The slope and scatter of the relation however appear to be a consequence of the seeding mechanism and the self-regulation prescription. We expect flux limited active galactic nucleus surveys to select MBHs that have already migrated on to the M<SUB>BH</SUB>-σ relation. Similarly, the Laser Interferometer Space Antenna (LISA) is also likely to be biased towards detecting merging MBHs that preferentially inhabit the M<SUB>BH</SUB>-σ. These results are a consequence of major mergers being more common at high redshift for the most massive, biased, galaxies that host MBHs which have already migrated on to the M<SUB>BH</SUB>-σ relation. We also predict the existence of a large population of low-mass `hidden' MBHs at high redshift which can easily escape detection. Additionally, we find that if MBH seeds are massive, ~10<SUP>5</SUP>M<SUB>solar</SUB>, the low-mass end of the M<SUB>BH</SUB>-σ flattens towards an asymptotic value, creating a characteristic `plume'.

[]

https://arxiv.org/pdf/0903.2262.pdf

2004ApJ...613.1143B

Massive Black Holes in Star Clusters. II. Realistic Cluster Models

2004-01-01

['black hole physics', 'galaxy globular clusters', 'methods n body', 'stars kinematics and dynamics', 'astrophysics']

[]

We have followed the evolution of multimass star clusters containing massive central black holes through collisional N-body simulations done on GRAPE6. Each cluster is composed of between 16,384 and 131,072 stars together with a black hole with an initial mass of M<SUB>BH</SUB>=1000M<SUB>solar</SUB>. We follow the evolution of the clusters under the combined influence of two-body relaxation, stellar mass loss, and tidal disruption of stars by the massive central black hole. We find that the (three-dimensional) mass density profile follows a power-law distribution ρ~r<SUP>-α</SUP> with slope α=1.55 inside the sphere of influence of the central black hole. This leads to a constant-density profile of bright stars in projection, which makes it highly unlikely that core-collapse clusters contain intermediate-mass black holes (IMBHs). Instead, globular clusters containing massive central black holes can be fitted with standard King profiles. Because of energy generation in the cusp, star clusters with IMBHs expand. The cluster expansion is so strong that clusters that start very concentrated can end up among the least dense clusters. The amount of mass segregation in the core is also smaller compared to postcollapse clusters without IMBHs. Most stellar mass black holes with masses M<SUB>BH</SUB>&gt;5M<SUB>solar</SUB> are lost from the clusters within a few gigayears through mutual encounters in the cusp around the IMBH. Black holes in star clusters disrupt mainly main-sequence stars and giants and no neutron stars. The disruption rates are too small to form an IMBH out of a M<SUB>BH</SUB>~50M<SUB>solar</SUB> progenitor black hole even if all material from disrupted stars is accreted onto the black hole, unless star clusters start with central densities significantly higher than what is seen in present-day globular clusters. We also discuss the possible detection mechanisms for IMBHs. Our simulations show that kinematical studies can reveal 1000M<SUB>solar</SUB> IMBHs in the closest clusters. IMBHs in globular clusters are weak X-ray sources, since the tidal disruption rate of stars is low and the star closest to the IMBH is normally another black hole, which prevents other stars from undergoing stable mass transfer. For globular clusters, dynamical evolution can push compact stars near the IMBH to distances small enough that they become detectable sources of gravitational radiation. If 10% of all globular clusters contain IMBHs, extragalactic globular clusters could be one of the major sources of gravitational wave events for LISA.

[]

https://arxiv.org/pdf/astro-ph/0406231.pdf

1994grra.conf....1P

Black Hole Information

1994-01-01

['-', '-']

[]

Hawking's 1974 calculation of thermal emission from a classical black hole led to his 1976 proposal that information may be lost from our universe as a pure quantum state collapses gravitationally into a black hole, which then evaporates completely into a mixed state of thermal radiation. Another possibility is that the information is not lost, but is stored in a remnant of the evaporating black hole. A third idea is that the information comes out in nonthermal correlations within the Hawking radiation, which would be expected to occur at too slow a rate, or be too spread out, to be revealed by any nonperturbative calculation.

[]

https://arxiv.org/pdf/hep-th/9305040.pdf

2008PhRvD..78b4016R

Thermodynamic curvature and phase transitions in Kerr-Newman black holes

2008-01-01

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

[]

Singularities in the thermodynamics of Kerr-Newman black holes are commonly associated with phase transitions. However, such interpretations are complicated by a lack of stability and, more significantly, by a lack of conclusive insight from microscopic models. Here, I focus on the later problem. I use the thermodynamic Riemannian curvature scalar R as a try to get microscopic information from the known thermodynamics. The hope is that this could facilitate matching black hole thermodynamics to known models of statistical mechanics. For the Kerr-Newman black hole, the sign of R is mostly positive, in contrast to that for ordinary thermodynamic models, where R is mostly negative. Cases with negative R include most of the simple critical point models. An exception is the Fermi gas, which has positive R. I demonstrate several exact correspondences between the two-dimensional Fermi gas and the extremal Kerr-Newman black hole. Away from the extremal case, R diverges to +∞ along curves of diverging heat capacities C<SUB>J,Φ</SUB> and C<SUB>Ω,Q</SUB>, but not along the Davies curve of diverging C<SUB>J,Q</SUB>. Finding statistical mechanical models with like behavior might yield additional insight into the microscopic properties of black holes. I also discuss a possible physical interpretation of |R|.

[]

https://arxiv.org/pdf/0802.1326.pdf

2007PhRvD..75f4030C

Spin flips and precession in black-hole-binary mergers

2007-01-01

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

[]

We use the “moving puncture” approach to perform fully nonlinear evolutions of spinning quasicircular black-hole binaries with individual spins unaligned with the orbital angular momentum. We evolve configurations with the individual spins (parallel and equal in magnitude) pointing in the orbital plane and 45° above the orbital plane. We introduce a technique to measure the spin direction and track the precession of the spin during the merger, as well as measure the spin flip in the remnant horizon. The former configuration completes 1.75 orbits before merging, with the spin precessing by 98° and the final remnant horizon spin flipped by ∼72° with respect to the component spins. The latter configuration completes 2.25 orbits, with the spins precessing by 151° and the final remnant horizon spin flipped ∼34° with respect to the component spins. These simulations show for the first time how the spins are reoriented during the final stage of black-hole-binary mergers verifying the hypothesis of the spin-flip phenomenon. We also compute the track of the holes before merger and observe a precession of the orbital plane with frequency similar to the orbital frequency and amplitude increasing with time.

[]

https://arxiv.org/pdf/gr-qc/0612076.pdf

2009ApJ...698..956C

Inspiralling Supermassive Black Holes: A New Signpost for Galaxy Mergers

2009-01-01

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

[]

We present a new technique for observationally identifying galaxy mergers spectroscopically rather than through host galaxy imaging. Our technique exploits the dynamics of supermassive black holes (SMBHs) powering active galactic nuclei (AGNs) in merger-remnant galaxies. Because structure in the universe is built up through galaxy mergers and nearly all galaxies host a central SMBH, some galaxies should possess two SMBHs near their centers as the result of a recent merger. These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power AGNs. Using the DEEP2 Galaxy Redshift Survey, we have examined 1881 red galaxies, of which 91 exhibit [O III] and Hβ emission lines indicative of Seyfert 2 activity. Of these, 32 AGNs have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ~50 km s<SUP>-1</SUP> to ~300 km s<SUP>-1</SUP>. Two of these AGNs exhibit double-peaked [O III] emission lines, while the remaining 30 AGNs each exhibit a single set of velocity-offset [O III] emission lines. After exploring a variety of physical models for these velocity offsets, we argue that the most likely explanation is inspiralling SMBHs in merger-remnant galaxies. Based on this interpretation, we find that roughly half of the red galaxies hosting AGNs are also merger remnants, which implies that mergers may trigger AGN activity in red galaxies. The AGN velocity offsets we find imply a merger fraction of ~30% and a merger rate of ~3 mergers Gyr<SUP>-1</SUP> for red galaxies at redshifts 0.34 &lt; z &lt; 0.82.

[]

https://arxiv.org/pdf/0810.3235.pdf

2003PhRvD..67f4020B

Quasinormal modes of Reissner Nordström anti-de Sitter black holes: Scalar, electromagnetic, and gravitational perturbations

2003-01-01

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

[]

We study scalar, electromagnetic and gravitational perturbations of a Reissner Nordström anti-de Sitter (RN-AdS) spacetime, and compute its quasinormal modes (QNM’s). We confirm and extend results previously found for Schwarzschild anti-de Sitter (S-AdS) black holes. For “large” black holes, whose horizon is much larger than the AdS radius, different classes of perturbations are almost exactly isospectral; this isospectrality is broken when the black hole’s horizon radius is comparable to the AdS radius. We provide very accurate fitting formulas for the QNM’s, which are valid for large black holes having charge Q&lt;Q<SUB>ext</SUB>/3 (Q<SUB>ext</SUB> being the extremal value of the charge). Electromagnetic and axial perturbations of large black holes are characterized by the existence of pure-imaginary (purely damped) modes. The damping of these modes tends to infinity as the black hole charge approaches the extremal value; if the corresponding mode amplitude does not tend to zero in the same limit, this implies that extremally charged RN-AdS black holes are marginally unstable. This result is relevant in view of the AdS conformal field theory conjecture, since, according to it, the AdS QNM’s give the time scales for the approach to equilibrium in the corresponding conformal field theory.

[]

https://arxiv.org/pdf/gr-qc/0301052.pdf

2006PhRvD..73j4030G

Dissipative effects in the worldline approach to black hole dynamics

2006-01-01

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

[]

We derive a long wavelength effective point-particle description of four-dimensional Schwarzschild black holes. In this effective theory, absorptive effects are incorporated by introducing degrees of freedom localized on the worldline that mimic the interaction between the horizon and bulk fields. The correlation functions of composite operators in this worldline theory can be obtained by standard matching calculations. For example, we obtain the low frequency two-point function of multipole worldline operators by relating them to the long wavelength graviton black hole absorptive cross section. The effective theory is then used to predict the leading effects of absorption in several astrophysically motivated examples, including the dynamics of nonrelativistic black hole binary inspirals and the motion of a small black hole in an arbitrary background geometry. Our results can be written compactly in terms of absorption cross sections, and can be easily applied to the dissipative dynamics of any compact object, e.g. neutron stars. The relation of our methodology to that developed in the context of the AdS/CFT correspondence is discussed.

[]

https://arxiv.org/pdf/hep-th/0511133.pdf

2015JHEP...09..184C

Holographic entanglement entropy and the extended phase structure of STU black holes

2015-01-01

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

[]

We study the extended thermodynamics, obtained by considering the cosmological constant as a thermodynamic variable, of STU black holes in 4-dimensions in the fixed charge ensemble. The associated phase structure is conjectured to be dual to an RG-flow on the space of field theories. We find that for some charge configurations the phase structure resembles that of a Van der Waals gas: the system exhibits a family of first order phase transitions ending in a second order phase transition at a critical temperature. We calculate the holographic entanglement entropy for several charge configurations and show that for the cases where the gravity background exhibits Van der Waals behavior, the entanglement entropy presents a transition at the same critical temperature. To further characterize the phase transition we calculate appropriate critical exponents and show that they coincide. Thus, the entanglement entropy successfully captures the information of the extended phase structure. Finally, we discuss the physical interpretation of the extended space in terms of the boundary QFT and construct various holographic heat engines dual to STU black holes.

[]

https://arxiv.org/pdf/1507.06069.pdf

2002MNRAS.332..165M

Coronal outflow dominated accretion discs: a new possibility for low-luminosity black holes?

2002-01-01

['accretion', 'accretion disks', 'black hole physics', 'stars magnetic fields', 'astrophysics']

[]

The spectral-energy distributions of galactic black holes in the low/hard state and of low-luminosity active galactic nuclei (AGNs) possess many common features, the most prominent being: compact, flat- (or inverted-)spectrum radio cores with high brightness temperatures; excess red and infrared emission, often correlated with the radio flux; an extremely weak (or absent) quasi-thermal hump and a hard-X-ray power-law with high-energy cut-off. These sources are thought to be accreting at low rates, and advection- (or convection-)dominated accretion flows are usually considered the best candidates to explain them. Here we present an alternative possibility, involving strong, unbound, magnetic coronae generated by geometrically thin, optically thick accretion discs at low accretion rates. First we show that, if angular momentum transport in the disc is due to magnetic turbulent stresses, the magnetic energy density and effective viscous stresses inside the disc are proportional to the geometric mean of the total (gas plus radiation) and gas pressure. Therefore the corona is less powerful in a radiation-pressure dominated disc, and the relative fraction of the power liberated in the corona increases as the accretion rate decreases. Furthermore, we discuss why energetically dominant coronae are ideal sites for launching powerful jets/outflows, both MHD- and thermally driven. In analysing the spectral properties of such coronal-outflow dominated accretion discs, we reach the important conclusion that if the jet/outflow is, as is likely, radiatively inefficient, then so is the source overall, even without advection of energy into the black hole being relevant for the dynamics of the accretion flow.

[]

https://arxiv.org/pdf/astro-ph/0112451.pdf

2006ApJ...647..525D

Testing Accretion Disk Theory in Black Hole X-Ray Binaries

2006-01-01

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

[]

We present results from spectral modeling of three black hole X-ray binaries: LMC X-3, GRO J1655-40, and XTE J1550-564. Using a sample of disk-dominated observations, we fit the data with a range of spectral models that includes a simple multitemperature blackbody (DISKBB), a relativistic accretion disk model based on color-corrected blackbodies (KERRBB), and a relativistic model based on non-LTE atmosphere models within an α prescription (BHSPEC). BHSPEC provides the best fit for a BeppoSAX observation of LMC X-3, which has the broadest energy coverage of our sample. It also provides the best fit for multiple epochs of Rossi X-Ray Timing Explorer (RXTE) data in this source, except at the very highest luminosity (L/L<SUB>Edd</SUB>&gt;~0.7), where additional physics must be coming into play. BHSPEC is also the best-fit model for multiepoch RXTE observations of GRO J1655-40 and XTE J1550-564, although the best-fit inclination of the inner disk differs from the binary inclination. All our fits prefer α=0.01 to α=0.1, in apparent disagreement with the large stresses inferred from the rapid rise times observed in outbursts of these two sources. In all three sources our fits imply moderate black hole spins (a<SUB>*</SUB>~0.1-0.8), but this is sensitive to the reliability of independent measurements of these system parameters and to the physical assumptions that underly our spectral models.

[]

https://arxiv.org/pdf/astro-ph/0602245.pdf

1996NuPhB.458..249L

Renormalization of black hole entropy and of the gravitational coupling constant

1996-01-01

['-']

[]

The quantum corrections to black hole entropy, variously defined, suffer quadratic divergences reminiscent of the ones found in the renormalization of the gravitational coupling constant (Newton constant). We consider the suggestion, due to Susskind and Uglum, that these divergences are proportional, and attempt to clarify its precise meaning. We argue that if the black hole entropy is identified using a Euclidean formulation, including the necessary surface term as proposed by Gibbons and Hawking, then the proportionality is, up to small identifiable corrections, a fairly immediate consequence of basic principles - a low-energy theorem. Thus in this framework renormalizing the Newton constant renders the entropy finite, and equal, in the limit of large mass, to its semiclassical value. As a partial check on our formal arguments we compare the one loop determinants, calculated using heat kernel regularization. An alternative definition of black hole entropy relates it to behavior at conical singularities in two dimensions, and thus to a suitable definition of geometric entropy. A definition of geometric entropy, natural from the point of view of heat kernel regularization, permits the same renormalization, but it does not yield an intrinsically positive quantity. The possibility, for scalar fields, of non-minimal coupling to background curvature allows one to consider test the framework in a continuous family of theories, and crucially involves a subtle sensitivity of geometric entropy to curved space couplings. Fermions and gauge fields are considered as well. Their functional determinants are closely related to the determinants for non-minimally coupled scalar fields with specific values for the curvature coupling, and pose no further difficulties.

[]

https://arxiv.org/pdf/hep-th/9506066.pdf

2012Sci...338...84M

The Shortest-Known-Period Star Orbiting Our Galaxy’s Supermassive Black Hole

2012-01-01

['-', '-']

[]

Stars with short orbital periods at the center of our Galaxy offer a powerful probe of a supermassive black hole. Over the past 17 years, the W. M. Keck Observatory has been used to image the galactic center at the highest angular resolution possible today. By adding to this data set and advancing methodologies, we have detected S0-102, a star orbiting our Galaxy’s supermassive black hole with a period of just 11.5 years. S0-102 doubles the number of known stars with full phase coverage and periods of less than 20 years. It thereby provides the opportunity, with future measurements, to resolve degeneracies in the parameters describing the central gravitational potential and to test Einstein’s theory of general relativity in an unexplored regime.

[]

https://arxiv.org/pdf/1210.1294.pdf

2020PhRvL.125j1101D

Neutrino and Positron Constraints on Spinning Primordial Black Hole Dark Matter

2020-01-01

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

[]

Primordial black holes can have substantial spin—a fundamental property that has a strong effect on its evaporation rate. We conduct a comprehensive study of the detectability of primordial black holes with non-negligible spin, via the searches for the neutrinos and positrons in the MeV energy range. Diffuse supernova neutrino background searches and observation of the 511 keV gamma-ray line from positrons in the Galactic center set competitive constraints. Spinning primordial black holes are probed up to a slightly higher mass range compared to nonspinning ones. Our constraint using neutrinos is slightly weaker than that due to the diffuse gamma-ray background, but complementary and robust. Our positron constraints are typically weaker in the lower mass range and stronger in the higher mass range for the spinning primordial black holes compared to the nonspinning ones. They are generally stronger than those derived from the diffuse gamma-ray measurements for primordial black holes having masses greater than a few ×10<SUP>16</SUP> g .

[]

https://arxiv.org/pdf/1912.01014.pdf

2022ApJ...924L..32R

Black Hole Flares: Ejection of Accreted Magnetic Flux through 3D Plasmoid-mediated Reconnection

2022-01-01

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

[]

Magnetic reconnection can power bright, rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high-resolution (5376 × 2304 × 2304 cells) general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated reconnection in a 3D magnetically arrested disk for the first time. We show that an equatorial, plasmoid-unstable current sheet forms in a transient, nonaxisymmetric, low-density magnetosphere within the inner few Schwarzschild radii. Magnetic flux bundles escape from the event horizon through reconnection at the universal plasmoid-mediated rate in this current sheet. The reconnection feeds on the highly magnetized plasma in the jets and heats the plasma that ends up trapped in flux bundles to temperatures proportional to the jet's magnetization. The escaped flux bundles can complete a full orbit as low-density hot spots, consistent with Sgr A* observations by the GRAVITY interferometer. Reconnection near the horizon produces sufficiently energetic plasma to explain flares from accreting black holes, such as the TeV emission observed from M87. The drop in the mass accretion rate during the flare and the resulting low-density magnetosphere make it easier for very-high-energy photons produced by reconnection-accelerated particles to escape. The extreme-resolution results in a converged plasmoid-mediated reconnection rate that directly determines the timescales and properties of the flare.

[]

https://arxiv.org/pdf/2109.15115.pdf

2018JHEP...09..048N

On the dynamics of near-extremal black holes

2018-01-01

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

[]

We analyse the dynamics of near-extremal Reissner-Nordström black holes in asymptotically four-dimensional Anti de Sitter space (AdS<SUB>4</SUB>). We work in the spherically symmetric approximation and study the thermodynamics and the response to a probe scalar field. We find that the behaviour of the system, at low energies and to leading order in our approximations, is well described by the Jackiw-Teitelboim (JT) model of gravity. In fact, this behaviour can be understood from symmetry considerations and arises due to the breaking of time reparametrisation invariance. The JT model has been analysed in considerable detail recently and related to the behaviour of the SYK model. Our results indicate that features in these models which arise from symmetry considerations alone are more general and present quite universally in near-extremal black holes.

[]

https://arxiv.org/pdf/1802.09547.pdf

2017JCAP...04..027B

Asymptotically flat black holes in Horndeski theory and beyond

2017-01-01

['-', '-']

[]

We find spherically symmetric and static black holes in shift-symmetric Horndeski and beyond Horndeski theories. They are asymptotically flat and sourced by a non trivial static scalar field. The first class of solutions is constructed in such a way that the Noether current associated with shift symmetry vanishes, while the scalar field cannot be trivial. This in certain cases leads to hairy black hole solutions (for the quartic Horndeski Lagrangian), and in others to singular solutions (for a Gauss-Bonnet term). Additionally, we find the general spherically symmetric and static solutions for a pure quartic Lagrangian, the metric of which is Schwarzschild. We show that under two requirements on the theory in question, any vacuum GR solution is also solution to the quartic theory. As an example, we show that a Kerr black hole with a non-trivial scalar field is an exact solution to these theories.

[]

https://arxiv.org/pdf/1702.01938.pdf

2014PTEP.2014d3E02Y

Gravitational radiation from an axion cloud around a black hole: Superradiant phase

2014-01-01

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

[]

Motivated by the possible existence of string axions with ultralight masses, we study gravitational radiation from an axion cloud around a rotating black hole (BH). The axion cloud extracts the rotation energy of the BH by superradiant instability, while it loses energy through the emission of gravitational waves (GWs). In this paper, GWs are treated as perturbations on a fixed background spacetime to derive the energy emission rate. We give an analytic approximate formula for the case where the axion Compton wavelength is much larger than the BH radius, and then present numerical results without approximation. The energy loss rate of the axion cloud through GW emission turns out to be smaller than the energy gain rate of the axion cloud by superradiant instability until nonlinear self-interactions of axions become important. In particular, an axion bosenova must happen at the last stage of superradiant instability.

[]

https://arxiv.org/pdf/1312.2326.pdf

2019Natur.575..618L

A wide star-black-hole binary system from radial-velocity measurements

2019-01-01

['-', '-']

[]

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun<SUP>1-4</SUP>. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries<SUP>5,6</SUP>. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68<SUB>-13</SUB><SUP>+11</SUP> solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories.

[]

https://arxiv.org/pdf/1911.11989.pdf

2012PhRvD..85b4017N

Critical phenomena and thermodynamic geometry of Reissner-Nordström-anti-de Sitter black holes

2012-01-01

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

[]

The phase transition of Reissner-Nordström black holes in (n+1)-dimensional anti-de Sitter spacetime is studied in detail using the thermodynamic analogy between a RN-AdS black hole and a van der Waals liquid-gas system. We first investigate critical phenomena of the RN-AdS black hole. The critical exponents of relevant thermodynamical quantities are evaluated. We find identical exponents for a RN-AdS black hole and a van der Waals liquid-gas system. This suggests a possible universality in the phase transitions of these systems. We finally study the thermodynamic behavior using the equilibrium thermodynamic state space geometry and find that the scalar curvature diverges exactly at the van der Waals-like critical point where the heat capacity at constant charge of the black hole diverges.

[]

https://arxiv.org/pdf/1104.3066.pdf

2014PhRvD..90h4009R

New parametrization for spherically symmetric black holes in metric theories of gravity

2014-01-01

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

[]

We propose a new parametric framework to describe in generic metric theories of gravity the spacetime of spherically symmetric and slowly rotating black holes. In contrast to similar approaches proposed so far, we do not use a Taylor expansion in powers of M/r, where M and r are the mass of the black hole and a generic radial coordinate, respectively. Rather, we use a continued-fraction expansion in terms of a compactified radial coordinate. This choice leads to superior convergence properties and allows us to approximate a number of known metric theories with a much smaller set of coefficients. The measure of these coefficients via observations of near-horizon processes can be used to effectively constrain and compare arbitrary metric theories of gravity. Although our attention is here focussed on spherically symmetric black holes, we also discuss how our approach could be extended to rotating black holes.

[]

https://arxiv.org/pdf/1407.3086.pdf

1992PhLB..292...13R

Black hole evaporation in 1+1 dimensions

1992-01-01

['-']

[]

The formation and quantum mechanical evaporation of black holes in two spacetime dimensions can be studied using effective classical field equations, recently introduced by Callan et al. We find that gravitational collapse always leads to a curvature singularity, according to these equations, and that the region where the quantum corrections introduced by Callan et al. could be expected to dominate is on the unphysical side of the singularity. The model can be successfully applied to study the back-reaction of Hawking radiation on the geometry of large mass black holes, but the description breaks down before the evaporation is complete.

[]

https://arxiv.org/pdf/hep-th/9201074.pdf

1998PhRvD..58f4011P

An action for black hole membranes

1998-01-01

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

[]

The membrane paradigm is the remarkable view that, to an external observer, a black hole appears to behave exactly like a dynamical fluid membrane, obeying such pre-relativistic equations as Ohm's law and the Navier-Stokes equation. It has traditionally been derived by manipulating the equations of motion. Here we provide an action formulation of this picture, clarifying what underlies the paradigm and simplifying the derivations. Within this framework, we derive previous membrane results, and extend them to dyonic black hole solutions. We discuss how it is that an action can produce dissipative equations. Using a Euclidean path integral, we show that familiar semi-classical thermodynamic properties of black holes also emerge from the membrane action. Finally, in a Hamiltonian description, we establish the validity of a minimum entropy production principle for black holes.

[]

https://arxiv.org/pdf/gr-qc/9712077.pdf

2000ApJS..130..463I

Two-dimensional Models of Hydrodynamical Accretion Flows into Black Holes

2000-01-01

['accretion', 'accretion disks', 'conductive heat transfer', 'atmosphere', 'hydrodynamics', 'turbulence', 'astrophysics']

[]

We present a systematic numerical study of two-dimensional axisymmetric accretion flows around black holes. The flows have no radiative cooling and are treated in the framework of the viscous hydrodynamic approximation. The models calculated in this study cover the large range of the relevant parameter space. There are four types of flows, determined by the values of the viscosity parameter α and the adiabatic index γ: convective flows, large-scale circulations, pure inflows, and bipolar outflows. Thermal conduction introduces significant changes to the solutions but does not create a new flow type. Convective accretion flows and flows with large-scale circulations have significant outward-directed energy fluxes, which have important implications for the spectra and luminosities of accreting black holes.

[]

https://arxiv.org/pdf/astro-ph/0003397.pdf

1992PhRvD..46.1347G

Black holes and massive remnants

1992-01-01

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

[]

This paper examines the conundrum faced when one attempts to understand the dynamics of black hole formation and evaporation without abandoning unitary evolution. Previous efforts to resolve this puzzle assume that information escapes in corrections to the Hawking process, that an arbitrarily large amount of information is transmitted by a Planckian energy or contained in a Planck-sized remnant, or that the information is lost to another universe. Each of these possibilities has serious difficulties. This paper considers another alternative: remnants that carry large amounts of information and whose size and mass depend on their information content. The existence of such objects is suggested by attempts to incorporate a Planck-scale cutoff into physics. They would greatly alter the late stages of the evaporation process. The main drawback of this scenario is the apparent noncausal behavior behind the horizon.

[]

https://arxiv.org/pdf/hep-th/9203059.pdf

2006ApJ...645..900W

Cosmic Evolution of Black Holes and Spheroids. I. The M<SUB>BH</SUB>-σ Relation at z = 0.36

2006-01-01

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

[]

We test the evolution of the correlation between black hole mass and bulge velocity dispersion (M<SUB>BH</SUB>-σ), using a carefully selected sample of 14 Seyfert 1 galaxies at z=0.36+/-0.01. We measure velocity dispersion from stellar absorption lines around Mg b (5175 Å) and Fe (5270 Å) using high-S/N Keck spectra and estimate black hole mass from the Hβ line width and the optical luminosity at 5100 Å, based on the empirically calibrated photoionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at z=0.36 than locally. We investigate various sources of systematic uncertainties and find that those cannot account for the observed offset. The measured offset is ΔlogM<SUB>BH</SUB>=0.62+/-0.10+/-0.25 i.e., Δlogσ=0.15+/-0.03+/-0.06, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M<SUB>BH</SUB>-σ relation is the universal evolutionary endpoint. Along with two samples of active galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution with the best-fit linear relation: ΔlogM<SUB>BH</SUB>=(1.66+/-0.43)z+(0.04+/-0.09) with respect to the local relationship of Tremaine and coworkers, and ΔlogM<SUB>BH</SUB>=(1.55+/-0.46)z+(0.01+/-0.12) with respect to that of Ferrarese. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (&lt;σ&gt;=170 km s<SUP>-1</SUP>).

[]

https://arxiv.org/pdf/astro-ph/0603648.pdf

2001ApJ...551L..17L

The Radio Luminosity-Black Hole Mass Correlation for Quasars from the FIRST Bright Quasar Survey and a ``Unification Scheme'' for Radio-loud and Radio-quiet Quasars

2001-01-01

['galaxies active', 'galaxies quasars', 'astronomy radio', 'astrophysics']

[]

Several independent lines of evidence now point to a correlation between black hole mass M<SUB>bh</SUB> and radio luminosity. In this Letter, we discuss the correlation for quasars from the FIRST Bright Quasar Survey (FBQS) using black hole mass estimates from Hβ line widths. The FBQS objects fill in the gap between the radio-loud and radio-quiet quasars in the radio luminosity-optical luminosity plane, and we find that they fill the corresponding gap in the M<SUB>bh</SUB>-radio luminosity correlation. There is thus a continuous variation of radio luminosity with M<SUB>bh</SUB>, and no evidence for a ``switch'' at some set of critical parameter values that turns on powerful radio jets. By combining the FBQS data with that for quasars from the Palomar-Green survey, we find evidence for a dependence of radio luminosity on accretion rate relative to the Eddington limit, L/L<SUB>Edd</SUB>, as well as on M<SUB>bh</SUB>, consistent with the well-known radio-optical correlation for radio-loud quasars. We therefore suggest a new scheme to ``unify'' radio-loud and radio-quiet objects in which the radio luminosity scales proportional to M<SUP>1.9+/-0.2</SUP><SUB>bh</SUB>(L/L<SUB>Edd</SUB>)<SUP>1.0</SUP> for L/L<SUB>Edd</SUB>~0.1, with an apparently weaker accretion rate dependence at low L/L<SUB>Edd</SUB>. The scatter about this relation is +/-1.1 dex and may well hide significant contributions from other physical effects, such as the black hole spin and radio source environment.

[]

https://arxiv.org/pdf/astro-ph/0103087.pdf

2003PhRvD..67b4008M

de Sitter black hole with a conformally coupled scalar field in four dimensions

2003-01-01

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

[]

A four-dimensional black hole solution of the Einstein equations with a positive cosmological constant coupled to a conformal scalar field is given. There is a curvature singularity at the origin, and the scalar field has a divergence inside the event horizon. The electrically charged solution, which has a fixed charge-to-mass ratio, is also found. The quartic self-interacting coupling constant becomes bounded in terms of Newton’s constant and the cosmological constant. The solution satisfies both dominant and the strong energy conditions.

[]

https://arxiv.org/pdf/hep-th/0205319.pdf

2006A&A...456..439K

Refining the fundamental plane of accreting black holes

2006-01-01

['astronomy x rays', 'galaxies active', 'radiation', 'stars winds outflows', 'hydrodynamics', 'black hole physics', 'accretion', 'accretion disks', 'astrophysics']

[]

Context: .The idea of a unified description of supermassive and stellar black holes has been supported by the extension of the empirical radio/X-ray correlation from X-ray binaries to active galactic nuclei through the inclusion of a mass term. This has lead to the so-called fundamental plane of black hole activity in the black hole mass, radio and X-ray luminosity space. Two incarnations of this fundamental plane have so far been suggested using different underlying models and using two different samples of accreting black holes.<BR /> Aims: .We improve the parameter estimates of the fundamental plane and estimate the scatter of the sources around the plane in both samples. This is used to look for possible constraints on the proposed theoretical models. Furthermore, we search for selection effects due to the inclusion of different classes of AGN or distance effects.<BR /> Methods: .We present revised samples for both studies together with a refined statistical analysis using measured errors of the observables. This method is used to compare the two samples and infer parameters for the fundamental plane in a homogeneous way.<BR /> Results: .We show that strongly sub-Eddington objects in a state equivalent to the low/hard state of X-ray binaries follow the fundamental plane very tightly; the scatter is comparable to the measurement errors. However, we find that the estimated parameters depend strongly on the assumptions made on the sources of scatter and the relative weight of the different AGN classes in the sample. Using only hard state objects, the fundamental plane is in agreement with the prediction of a simple uncooled synchrotron/jet model for the emitted radiation. Inclusion of high-state objects increases the scatter and moves the correlation closer to a disk/jet model. This is qualitatively consistent with a picture where low-state objects are largely dominated by jet emission while high-state objects have a strong contribution from an accretion disk.<BR />

[]

https://arxiv.org/pdf/astro-ph/0603117.pdf

2005JHEP...07..009C

Superradiant instabilities of rotating black branes and strings

2005-01-01

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

[]

Black branes and strings are generally unstable against a certain sector of gravitational perturbations. This is known as the Gregory-Laflamme instability. It has been recently argued [1], [2] that there exists another general instability affecting many rotating extended black objects. This instability is in a sense universal, in that it is triggered by any massless field, and not just gravitational perturbations. Here we investigate this novel mechanism in detail. For this instability to work, two ingredients are necessary: (i) an ergo-region, which gives rise to superradiant amplification of waves, and (ii) ``bound'' states in the effective potential governing the evolution of the particular mode under study. We show that the black brane Kerr<SUB>4</SUB>×R<SUP>p</SUP> is unstable against this mechanism, and we present numerical results for instability timescales for this case. On the other hand, and quite surprisingly, black branes of the form Kerr<SUB>d</SUB>×R<SUP>p</SUP> are all stable against this mechanism for d &gt; 4. This is quite an unexpected result, and it stems from the fact that there are no stable circular orbits in higher dimensional black hole spacetimes, or in a wave picture, that there are no bound states in the effective potential. We also show that it is quite easy to simulate this instability in the laboratory with acoustic black branes.

[]

https://arxiv.org/pdf/hep-th/0502206.pdf

2001ApJ...558..535M

The Merger History of Supermassive Black Holes in Galaxies

2001-01-01

['black hole physics', 'cosmology theory', 'galaxies active', 'galaxies nuclei', 'gravitation', 'galaxies quasars', 'astrophysics', '-']

[]

The ubiquity of supermassive black holes (SMBHs) at the centers of nearby luminous galaxies can arise from the multiple mergers experienced by dark matter halos in hierarchical structure formation models, even if only a small fraction of these galaxies harbor SMBHs at high redshifts. We illustrate this possibility using cosmological Monte Carlo simulations of the merger history of dark matter halos and their associated SMBHs. In our most extreme models, in order to populate nearly every bright galaxy with an SMBH at z=0, only a few percent of the halos with virial temperatures above 10<SUP>4</SUP> K are required to harbor an SMBH at high redshift. This possibility must be included in studies of the luminosity function and the clustering properties of quasars. We predict the number of SMBH merger events that are detectable by the gravitational wave experiment Laser Interferometer Space Antenna (LISA), as a function of redshift, out to z=5. Although the event rates can be significantly reduced in scenarios with rare SMBHs, a minimum of ~10 detectable merger events per year is predicted if SMBH binaries coalesce efficiently. The observed distribution of events with redshift could yield valuable information on the SMBH formation process. If SMBH binaries do not coalesce, we find that at least several SMBH slingshot ejections probably occurred from z=5 to the present in each galaxy more massive than ~10<SUP>11</SUP> M<SUB>solar</SUB> at z=0. Although our results are sensitive to the minimum cooling mass assumed for the formation of SMBHs, we expect the qualitative predictions of our models to be robust.

[]

https://arxiv.org/pdf/astro-ph/0101196.pdf

2011MNRAS.415.3033R

Limiting eccentricity of subparsec massive black hole binaries surrounded by self-gravitating gas discs

2011-01-01

['accretion', 'accretion disks', 'black hole physics', 'gravitational waves', 'methods numerical', '-']

[]

We study the dynamics of supermassive black hole binaries embedded in circumbinary gaseous discs, with the smoothed particle hydrodynamics code GADGET-2. The subparsec binary (of total mass M and mass ratio q= 1/3) has excavated a gap and transfers its angular momentum to the self-gravitating disc (M<SUB>disc</SUB>= 0.2M). We explore the changes of the binary eccentricity, e, by simulating a sequence of binary models that differ in the initial eccentricity e<SUB>0</SUB> only. In initially low-eccentric binaries, the eccentricity increases with time, while in high-eccentric binaries e declines, indicating the existence of a limiting eccentricity e<SUB>crit</SUB> that is found to fall in the interval [0.6, 0.8]. We also present an analytical interpretation for this saturation limit. An important consequence of the existence of e<SUB>crit</SUB> is the detectability of a significant residual eccentricity e<SUB>LISA</SUB> by the proposed gravitational wave detector Laser Interferometer Space Antenna (LISA). It is found that at the moment of entering the LISA frequency domain e<SUB>LISA</SUB>∼ 10<SUP>-3</SUP>-10<SUP>-2</SUP>, a signature of its earlier coupling with the massive circumbinary disc. We also observe large periodic inflows across the gap, occurring on the binary and disc dynamical time-scales rather than on the viscous time. These periodic changes in the accretion rate (with amplitudes up to ∼100 per cent, depending on the binary eccentricity) can be considered a fingerprint of eccentric subparsec binaries migrating inside a circumbinary disc.

[]

https://arxiv.org/pdf/1104.3868.pdf

2013MNRAS.432.2779B

Dynamical evolution of black hole subsystems in idealized star clusters

2013-01-01

['methods numerical', 'clusters globular', '-']

[]

In this paper, globular star clusters which contain a subsystem of stellar mass black holes (BH) are investigated. This is done by considering two-component models, as these are the simplest approximation of more realistic multimass systems, where one component represents the BH population and the other represents all the other stars. These systems are found to undergo a long phase of evolution where the centre of the system is dominated by a dense BH subsystem. After mass segregation has driven most of the BH into a compact subsystem, the evolution of the BH subsystem is found to be influenced by the cluster in which it is contained. The BH subsystem evolves in such a way as to satisfy the energy demands of the whole cluster, just as the core of a one-component system must satisfy the energy demands of the whole cluster. The BH subsystem is found to exist for a significant amount of time. It takes approximately 10t<SUB>rh,i</SUB>, where t<SUB>rh,i</SUB> is the initial half-mass relaxation time, from the formation of the compact BH subsystem up until the time when 90 per cent of the subsystem total mass is lost (which is 10<SUP>3</SUP> times the half-mass relaxation time of the BH subsystem at its time of formation). Based on theoretical arguments, the rate of mass-loss from the BH subsystem (Mdot<SUB>2</SUB>) is predicted to be -βζM/(αt<SUB>rh</SUB>), where M is the total mass, t<SUB>rh</SUB> is the half-mass relaxation time and α, β, ζ are three dimensionless parameters (see Section 2 of the main text for details). An interesting consequence of this is that the rate of mass-loss from the BH subsystem is approximately independent of the stellar mass ratio (m<SUB>2</SUB>/m<SUB>1</SUB>) and the total mass ratio (M<SUB>2</SUB>/M<SUB>1</SUB>) (in the range m<SUB>2</SUB>/m<SUB>1</SUB> ≳ 10 and M<SUB>2</SUB>/M<SUB>1</SUB> ∼ 10<SUP>-2</SUP>, where m<SUB>1</SUB> and m<SUB>2</SUB> are the masses of individual low-mass and high-mass particles, respectively, and M<SUB>1</SUB> and M<SUB>2</SUB> are the corresponding total masses). The theory is found to be in reasonable agreement with most of the results of a series of N-body simulations, and with all of the models if the value of ζ is suitably adjusted. Predictions based on theoretical arguments are also made about the structure of BH subsystems. Other aspects of the evolution are also considered such as the conditions for the onset of gravothermal oscillation.

[]

https://arxiv.org/pdf/1304.3401.pdf

2009PhRvD..79d4012M

Lovelock black holes with a nonlinear Maxwell field

2009-01-01

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

[]

We derive electrically charged black hole solutions of the Einstein-Gauss-Bonnet equations with a nonlinear electrodynamics source in n(≥5) dimensions. The spacetimes are given as a warped product M<SUP>2</SUP>×K<SUP>n-2</SUP>, where K<SUP>n-2</SUP> is a (n-2)-dimensional constant curvature space. We establish a generalized Birkhoff’s theorem by showing that it is the unique electrically charged solution with this isometry and for which the orbit of the warp factor on K<SUP>n-2</SUP> is non-null. An extension of the analysis for full Lovelock gravity is also achieved with a particular attention to the Chern-Simons case.

[]

https://arxiv.org/pdf/0812.2038.pdf

2021PhRvL.126a1103H

Spin-Induced Scalarized Black Holes

2021-01-01

['-', '-']

[]

It was recently shown that a scalar field suitably coupled to the Gauss-Bonnet invariant G can undergo a spin-induced linear tachyonic instability near a Kerr black hole. This instability appears only once the dimensionless spin j is sufficiently large, that is, j ≳0.5 . A tachyonic instability is the hallmark of spontaneous scalarization. Focusing, for illustrative purposes, on a class of theories that do exhibit this instability, we show that stationary, rotating black hole solutions do indeed have scalar hair once the spin-induced instability threshold is exceeded, while black holes that lie below the threshold are described by the Kerr solution. Our results provide strong support for spin-induced black hole scalarization.

[]

https://arxiv.org/pdf/2009.03904.pdf

2004PhRvD..70d2001V

LISA observations of rapidly spinning massive black hole binary systems

2004-01-01

['-', '-', '-', '-', '-', '-', 'stars luminosity function;mass function', '-', '-', 'black hole physics', 'astrophysics', '-']

[]

Binary systems of massive black holes will be detectable by the Laser Interferometer Space Antenna (LISA) throughout the entire Universe. Observations of gravitational waves from this class of sources will have important repercussions on our understanding of the behavior of gravity in the highly nonlinear relativistic regime, the distribution and interaction of massive black holes at high redshift, and the formation and evolution of cosmic structures. It is therefore important to address how accurately LISA can measure the source parameters and explore the implications for astronomy and cosmology. Present observations and theoretical models suggest that massive black holes could be spinning, possibly rapidly in some cases. In binary systems, the relativistic spin-orbit interaction causes the orbital plane to precess in space, producing a characteristic signature on the emitted gravitational waves. In this paper we investigate the effect of spins on the gravitational wave signal registered at the LISA output—we provide ready-to-use analytical expressions of the measured signal—and the implications for parameter estimation. We consider the inspiral phase of binary systems in circular orbit undergoing the so-called “simple precession” and we approximate the gravitational radiation at the restricted post<SUP>1.5</SUP>-Newtonian order. We show that the presence of spins changes dramatically the signature of the signal recorded by LISA. As a consequence, the mean square errors associated with the parameter measurements are significantly smaller than the ones obtained when the effect of spins is neglected. For a binary system of two 10<SUP>6</SUP>M<SUB>⊙</SUB> black holes, the angular resolution and the relative error on the luminosity distance improve by a factor of ≈3 10; the fractional errors on the chirp mass and the reduced mass decrease by a factor of ∼10 and ∼10<SUP>3</SUP>, respectively.

[]

https://arxiv.org/pdf/astro-ph/0304051.pdf

2005ApJ...634..921A

Eccentricity of Supermassive Black Hole Binaries Coalescing from Gas-rich Mergers

2005-01-01

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

[]

Angular momentum loss to circumbinary gas provides a possible mechanism for overcoming the ``last parsec'' problem and allowing the most massive black hole binaries formed from galactic mergers to coalesce. Here we show that if gas disks also catalyze the merger of the somewhat lower mass binaries detectable with the Laser Interferometer Space Antenna (LISA), then there may be a purely gravitational wave signature of the role of gas in the form of a small but finite eccentricity just prior to merger. Numerical simulations suggest that eccentricity, excited by the interaction between the binary and surrounding gas disk, is only partially damped during the final phase of gravitational radiation-driven inspiral. We estimate a typical eccentricity at 1 week prior to coalescence of e~0.01. Higher terminal eccentricities, which can approach e=0.1, are possible if the binary has an extreme mass ratio. The detection of even a small eccentricity prior to merger by LISA provides a possible discriminant between gas-driven inspirals and those effected by stellar processes.

[]

https://arxiv.org/pdf/astro-ph/0508493.pdf

2005Natur.436..666M

The obscuration by dust of most of the growth of supermassive black holes

2005-01-01

['astrophysics']

[]

Supermassive black holes underwent periods of exponential growth during which we see them as quasars in the distant Universe. The summed emission from these quasars generates the cosmic X-ray background, the spectrum of which has been used to argue that most black-hole growth is obscured. There are clear examples of obscured black-hole growth in the form of `type-2' quasars, but their numbers are fewer than expected from modelling of the X-ray background. Here we report the direct detection of a population of distant type-2 quasars, which is at least comparable in size to the well-known unobscured type-1 population. We selected objects that have mid-infrared and radio emissions characteristic of quasars, but which are faint at near-infrared and optical wavelengths. We conclude that this population is responsible for most of the black-hole growth in the young Universe and that, throughout cosmic history, black-hole growth occurs in the dusty, gas-rich centres of active galaxies.

[]

https://arxiv.org/pdf/astro-ph/0505486.pdf

2007PhRvD..76f4028D

Faithful effective-one-body waveforms of small-mass-ratio coalescing black hole binaries

2007-01-01

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

[]

We address the problem of constructing high-accuracy, faithful analytic waveforms describing the gravitational wave signal emitted by inspiralling and coalescing binary black holes. We work within the effective-one-body (EOB) framework and propose a methodology for improving the current (waveform) implementations of this framework based on understanding, element by element, the physics behind each feature of the waveform and on systematically comparing various EOB-based waveforms with exact waveforms obtained by numerical relativity approaches. The present paper focuses on small-mass-ratio nonspinning binary systems, which can be conveniently studied by Regge-Wheeler-Zerilli-type methods. Our results include (i) a resummed, 3 PN-accurate description of the inspiral waveform, (ii) a better description of radiation reaction during the plunge, (iii) a refined analytic expression for the plunge waveform, (iv) an improved treatment of the matching between the plunge and ring-down waveforms. This improved implementation of the EOB approach allows us to construct complete analytic waveforms which exhibit a remarkable agreement with the exact ones in modulus, frequency, and phase. In particular, the analytic and numerical waveforms stay in phase, during the whole process, within ±1.1% of a cycle. We expect that the extension of our methodology to the comparable-mass case will be able to generate comparably accurate analytic waveforms of direct use for the ground-based network of interferometric detectors of gravitational waves.

[]

https://arxiv.org/pdf/0705.2519.pdf

2005GReGr..37..635A

Four-parametric regular black hole solution

2005-01-01

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

[]

We present a regular class of exact black hole solutions of the Einstein equations coupled with a nonlinear electrodynamics source. For weak fields the nonlinear electrodynamics becomes the Maxwell theory, and asymptotically the solutions behave as the Reissner Nordström one. The class is endowed with four parameters, which can be thought of as the mass m, charge q, and a sort of dipole and quadrupole moments α and β, respectively. For α≥3, β≥4, and |q|≤2s<SUB>c</SUB> m the corresponding solutions are regular charged black holes. For α = 3, they also satisfy the weak energy condition. For α = β = 0 we recover the Reissner Nordström singular solution and for α = 3, β = 4 the family includes a previous regular black hole reported by the authors.

[]

https://arxiv.org/pdf/hep-th/0403229.pdf

1995PhRvD..51.2839G

Topology, entropy, and Witten index of dilaton black holes

1995-01-01

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

[]

We have found that for extreme dilaton black holes an inner boundary must be introduced in addition to the outer boundary to give an integer value to the Euler number. The resulting manifolds have (if one identifies imaginary time) a topology S<SUP>1</SUP>×R×S<SUP>2</SUP> and Euler number χ=0 in contrast with the nonextreme case with χ=2. The entropy of extreme U(1) dilaton black holes is already known to be zero. We include a review of some recent ideas due to Hawking on the Reissner-Nordström case. By regarding all extreme black holes as having an inner boundary, we conclude that the entropy of all extreme black holes, including [U(1)]<SUP>2</SUP> black holes, vanishes. We discuss the relevance of this to the vanishing of quantum corrections and the idea that the functional integral for extreme holes gives a Witten index. We have studied also the topology of ``moduli space'' of multi-black-holes. The quantum mechanics on black hole moduli spaces is expected to be supersymmetric despite the fact that they are not hyper-Kähler since the corresponding geometry has a torsion unlike the BPS monopole case. Finally, we describe the possibility of extreme black hole fission for states with an energy gap. The energy released, as a proportion of the initial rest mass, during the decay of an electromagnetic black hole is 300 times greater than that released by the fission of a <SUP>235</SUP>U nucleus.

[]

https://arxiv.org/pdf/hep-th/9407118.pdf

2004CQGra..21..273Z

Quasi-normal modes of Schwarzschild de Sitter black holes

2004-01-01

['-', '-']

[]

The low-lying frequencies of characteristic quasi-normal modes (QNMs) of Schwarzschild de Sitter (SdS) black holes have been calculated for fields of different spin using the sixth-order WKB approximation and the approximation by the Pöschl Teller potential. The well-known asymptotic formula for large l is generalized here in a case of the SdS black hole. In the limit of the near extreme Λ term the results given by both methods are in very good agreement, and in this limit fields of different spin decay with the same rate.

[]

https://arxiv.org/pdf/gr-qc/0307012.pdf

2013MNRAS.428..421S

Accretion-driven evolution of black holes: Eddington ratios, duty cycles and active galaxy fractions

2013-01-01

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

[]

We develop semi-empirical models of the supermassive black hole and active galactic nucleus (AGN) populations, which incorporate the black hole growth implied by the observed AGN luminosity function assuming a radiative efficiency ɛ and a distribution of Eddington ratios λ. By generalizing these continuity-equation models to allow a distribution P(λ | M<SUB>BH</SUB>, z), we are able to draw on constraints from observationally estimated λ distributions and active galaxy fractions while accounting for the luminosity thresholds of observational samples. We consider models with a Gaussian distribution of log λ and Gaussians augmented with a power-law tail to low λ. Within our framework, reproducing the high observed AGN fractions at low redshift requires a characteristic Eddington ratio λ<SUB>c</SUB> that declines at late times, and matching observed Eddington ratio distributions requires a P(λ) that broadens at low redshift. To reproduce the observed increase of AGN fraction with black hole or galaxy mass, we also require a λ<SUB>c</SUB> that decreases with increasing black hole mass, reducing the AGN luminosity associated with the most massive black holes. Finally, achieving a good match to the high-mass end of the local black hole mass function requires an increased radiative efficiency at high black hole mass. We discuss the potential impact of black hole mergers or a λ-dependent bolometric correction, and we compute evolutionary predictions for black hole and galaxy specific accretion rates. Despite the flexibility of our framework, no one model provides a good fit to all the data we consider; it is particularly difficult to reconcile the relatively narrow λ distributions and low duty cycles estimated for luminous broad-line AGN with the broader λ distributions and higher duty cycles found in more widely selected AGN samples, which typically have lower luminosity thresholds.

[]

https://arxiv.org/pdf/1111.3574.pdf

2005PhRvD..71f4004W

Strong gravitational lensing by braneworld black holes

2005-01-01

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

[]

In this paper, we use the strong field limit approach to investigate the gravitational lensing properties of braneworld black holes. Applying this method to the supermassive black hole at the center of our galaxy, the lensing observables for some candidate braneworld black hole metrics are compared with those for the standard Schwarzschild case. It is found that braneworld black holes could have significantly different observational signatures to the Schwarzschild black hole.

[]

https://arxiv.org/pdf/astro-ph/0411786.pdf

2011PhRvD..84b4038N

Exact Schwarzschild-de Sitter black holes in a family of massive gravity models

2011-01-01

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

[]

The Schwarzschild-de Sitter and Reissner-Nordström-de Sitter black hole metrics appear as exact solutions in the recently formulated massive gravity of de Rham, Gabadadze and Tolley, where the mass term sets the curvature scale. They occur within a two-parameter family of de Rham, Gabadadze and Tolley mass terms. They show no trace of a cloud of scalar graviton modes, and in the limit of vanishing graviton mass they go smoothly to the Schwarzschild and Reissner-Nordström metrics.

[]

https://arxiv.org/pdf/1103.5912.pdf

2014IJMPD..2330023C

Black hole thermodynamics

2014-01-01

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

[]

The discovery in the early 1970s that black holes radiate as black bodies has radically affected our understanding of general relativity, and offered us some early hints about the nature of quantum gravity. In this paper, will review the discovery of black hole thermodynamics and summarize the many independent ways of obtaining the thermodynamic and (perhaps) statistical mechanical properties of black holes. I will then describe some of the remaining puzzles, including the nature of the quantum microstates, the problem of universality, and the information loss paradox.

[]

https://arxiv.org/pdf/1410.1486.pdf

2013IJMPA..2840018P

Advanced Methods in Black-Hole Perturbation Theory

2013-01-01

['black hole physics', 'perturbation theory', 'gravitational waves', 'methods numerical', '-', '-', '-', '-', '-', 'perturbation theory', '-', '-', '-', '-', '-', '-']

[]

Black-hole perturbation theory is a useful tool to investigate issues in astrophysics, high-energy physics, and fundamental problems in gravity. It is often complementary to fully-fledged nonlinear evolutions and instrumental to interpret some results of numerical simulations. Several modern applications require advanced tools to investigate the linear dynamics of generic small perturbations around stationary black holes. Here, we present an overview of these applications and introduce extensions of the standard semianalytical methods to construct and solve the linearized field equations in curved space-time. Current state-of-the-art techniques are pedagogically explained and exciting open problems are presented.

[]

https://arxiv.org/pdf/1305.6759.pdf

2014Natur.513...74P

A 400-solar-mass black hole in the galaxy M82

2014-01-01

['-']

[]

M82 X-1, the brightest X-ray source in the galaxy M82, has been thought to be an intermediate-mass black hole (100 to 10,000 solar masses) because of its extremely high luminosity and variability characteristics, although some models suggest that its mass may be only about 20 solar masses. The previous mass estimates were based on scaling relations that use low-frequency characteristic timescales which have large intrinsic uncertainties. For stellar-mass black holes, we know that the high-frequency quasi-periodic oscillations (100-450 hertz) in the X-ray emission that occur in a 3:2 frequency ratio are stable and scale in frequency inversely with black hole mass with a reasonably small dispersion. The discovery of such stable oscillations thus potentially offers an alternative and less ambiguous means of mass determination for intermediate-mass black holes, but has hitherto not been realized. Here we report stable, twin-peak (3:2 frequency ratio) X-ray quasi-periodic oscillations from M82 X-1 at frequencies of 3.32 +/- 0.06 hertz and 5.07 +/- 0.06 hertz. Assuming that we can extrapolate the inverse-mass scaling that holds for stellar-mass black holes, we estimate the black hole mass of M82 X-1 to be 428 +/- 105 solar masses. In addition, we can estimate the mass using the relativistic precession model, from which we get a value of 415 +/- 63 solar masses.

[]

https://arxiv.org/pdf/1501.03180.pdf

2013ApJ...777..170J

Photon Rings around Kerr and Kerr-like Black Holes

2013-01-01

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

[]

Very long baseline interferometric observations have resolved structure on scales of only a few Schwarzschild radii around the supermassive black holes at the centers of our Galaxy and M87. In the near future, such observations are expected to image the shadows of these black holes together with a bright and narrow ring surrounding their shadows. For a Kerr black hole, the shape of this photon ring is nearly circular unless the black hole spins very rapidly. Whether or not, however, astrophysical black holes are truly described by the Kerr metric as encapsulated in the no-hair theorem still remains an untested assumption. For black holes that differ from Kerr black holes, photon rings have been shown numerically to be asymmetric for small to intermediate spins. In this paper, I calculate semi-analytic expressions of the shapes of photon rings around black holes described by a new Kerr-like metric which is valid for all spins. I show that photon rings in this spacetime are affected by two types of deviations from the Kerr metric which can cause the ring shape to be highly asymmetric. I argue that the ring asymmetry is a direct measure of a potential violation of the no-hair theorem and that both types of deviations can be detected independently if the mass and distance of the black hole are known. In addition, I obtain approximate expressions of the diameters, displacements, and asymmetries of photon rings around Kerr and Kerr-like black holes.

[]

https://arxiv.org/pdf/1501.02814.pdf

2020ApJ...902L..36F

Constraints from Gravitational-wave Detections of Binary Black Hole Mergers on the <SUP>12</SUP>C(α, γ)<SUP>16</SUP>O Rate

2020-01-01

['-', '-', '-', 'nuclear reactions;nucleosynthesis;abundances', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-']

[]

Gravitational-wave detections are starting to allow us to probe the physical processes in the evolution of very massive stars through the imprints they leave on their final remnants. Stellar evolution theory predicts the existence of a gap in the black hole mass distribution at high mass due to the effects of pair instability. Previously, we showed that the location of the gap is robust against model uncertainties, but it does depend sensitively on the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ rate. This rate is of great astrophysical significance and governs the production of oxygen at the expense of carbon. We use the open-source MESA stellar evolution code to evolve massive helium stars to probe the location of the mass gap. We find that the maximum black hole mass below the gap varies between $40\,{M}_{\odot }$ and $90\,{M}_{\odot }$ , depending on the strength of the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ reaction rate. With the first 10 gravitational-wave detections of black holes, we constrain the astrophysical S-factor for ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ , at $300\,\mathrm{keV}$ , to ${S}_{300}\gt 175\,\,{\rm{keV}}\,{\rm{b}}$ at 68% confidence. With ${ \mathcal O }(50)$ detected binary black hole mergers, we expect to constrain the S-factor to within ±10-30 ${\rm{keV}}\,{\rm{b}}$ . We also highlight a role for independent constraints from electromagnetic transient surveys. The unambiguous detection of pulsational pair-instability supernovae would imply that ${S}_{300}\gt 79\,{\rm{keV}}\,{\rm{b}}$ . Degeneracies with other model uncertainties need to be investigated further, but probing nuclear stellar astrophysics poses a promising science case for the future gravitational-wave detectors.

[]

https://arxiv.org/pdf/2006.06678.pdf

2012PhRvD..86j4062T

Can we distinguish between black holes and wormholes by their Einstein-ring systems?

2012-01-01

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

[]

For the past decade, gravitational lensing in the strong gravitational field has been studied eagerly. It is well known that, for the lensing by a black hole, an infinite number of Einstein rings are formed by the light rays which wind around the black hole nearly on the photon sphere, which are called relativistic Einstein rings. This is also the case for the lensing by a wormhole. In this paper, we study the Einstein ring and relativistic Einstein rings for the Schwarzschild black hole and the Ellis wormhole, the latter of which is an example of traversable wormholes of the Morris-Thorne class. Given the configuration of the gravitational lensing and the radii of the Einstein ring and relativistic Einstein rings, we can distinguish between a black hole and a wormhole in principle. We conclude that we can detect the relativistic Einstein rings by wormholes which have the radii of the throat a≃0.5pc at a Galactic center with the distance 10 Mpc and which have a≃10AU in our Galaxy using the most powerful modern instruments which have the resolution of 10<SUP>-2</SUP>arcsecond such as a 10-meter optical-infrared telescope. The black holes which make the Einstein rings of the same size as the ones by the wormholes are galactic supermassive black holes and the relativistic Einstein rings by the black holes are too small to measure with the current technology. We may test the hypotheses of astrophysical wormholes by using the Einstein ring and relativistic Einstein rings in the future.

[]

https://arxiv.org/pdf/1207.0047.pdf

2015ApJ...814...58D

Merger Rates of Double Neutron Stars and Stellar Origin Black Holes: The Impact of Initial Conditions on Binary Evolution Predictions

2015-01-01

['stars binaries close', 'gravitational waves', 'stars black holes', '-', '-', 'astronomy x rays', '-', '-']

[]

The initial mass function (IMF), binary fraction, and distributions of binary parameters (mass ratios, separations, and eccentricities) are indispensable inputs for simulations of stellar populations. It is often claimed that these are poorly constrained, significantly affecting evolutionary predictions. Recently, dedicated observing campaigns have provided new constraints on the initial conditions for massive stars. Findings include a larger close binary fraction and a stronger preference for very tight systems. We investigate the impact on the predicted merger rates of neutron stars and black holes. Despite the changes with previous assumptions, we only find an increase of less than a factor of 2 (insignificant compared with evolutionary uncertainties of typically a factor of 10-100). We further show that the uncertainties in the new initial binary properties do not significantly affect (within a factor of 2) our predictions of double compact object merger rates. An exception is the uncertainty in IMF (variations by a factor of 6 up and down). No significant changes in the distributions of final component masses, mass ratios, chirp masses, and delay times are found. We conclude that the predictions are, for practical purposes, robust against uncertainties in the initial conditions concerning binary parameters, with the exception of the IMF. This eliminates an important layer of the many uncertain assumptions affecting the predictions of merger detection rates with the gravitational wave detectors aLIGO/aVirgo.

[]

https://arxiv.org/pdf/1506.03573.pdf

2014MNRAS.439.2736D

Tracing the cosmic growth of supermassive black holes to z ∼ 3 with Herschel

2014-01-01

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

[]

We study a sample of Herschel selected galaxies within the Great Observatories Origins Deep Survey-South and the Cosmic Evolution Survey fields in the framework of the Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe project. Starting from the rich multiwavelength photometric data sets available in both fields, we perform a broad-band spectral energy distribution decomposition to disentangle the possible active galactic nucleus (AGN) contribution from that related to the host galaxy. We find that 37 per cent of the Herschel-selected sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability of revealing AGN activity increases for bright (L<SUB>1-1000</SUB> &gt; 10<SUP>11</SUP> L<SUB>⊙</SUB>) star-forming galaxies at z &gt; 0.3, becoming about 80 per cent for the brightest (L<SUB>1-1000</SUB> &gt; 10<SUP>12</SUP> L<SUB>⊙</SUB>) infrared (IR) galaxies at z ≥ 1. Finally, we reconstruct the AGN bolometric luminosity function and the supermassive black hole growth rate across cosmic time up to z ∼ 3 from a far-IR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global black hole growth peaking at z ∼ 2 and reproducing the observed local black hole mass density with consistent values of the radiative efficiency ɛ<SUB>rad</SUB> (∼0.07).

[]

https://arxiv.org/pdf/1401.4503.pdf

2021NatAs...5..749G

Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures

2021-01-01

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

[]

While most of the compact-binary mergers detected by LIGO and Virgo are expected to consist of first-generation black holes formed from the collapse of stars, others might instead be of second (or higher) generation, containing the remnants of previous black-hole mergers. We review theoretical findings, astrophysical modelling and current gravitational-wave evidence of hierarchical stellar-mass black-hole mergers. Such a subpopulation of hierarchically assembled black holes presents distinctive gravitational-wave signatures, namely higher masses, possibly within the pair-instability mass gap, and dimensionless spins clustered at the characteristic value of ~0.7. To produce hierarchical mergers, astrophysical environments need to overcome the relativistic recoils imparted to black-hole merger remnants, a condition that prefers hosts with escape speeds of ≳100 km s<SUP>−1</SUP>. Promising locations for efficient production of hierarchical mergers include nuclear star clusters and accretion disks surrounding active galactic nuclei, though environments that are less efficient at retaining merger products such as globular clusters may still contribute significantly to the detectable population of repeated mergers. While GW190521 is the single most promising hierarchical-merger candidate to date, constraints from large population analyses are becoming increasingly more powerful.

[]

https://arxiv.org/pdf/2105.03439.pdf

2008ApJ...679L.117S

r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole-Neutron Star Mergers

2008-01-01

['neutrinos', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', 'nuclear reactions;nucleosynthesis;abundances', '-', 'astrophysics', 'nuclear reactions;nucleosynthesis;abundances']

[]

We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.

[]

https://arxiv.org/pdf/0803.1785.pdf

2008MPLA...23.1801G

The Lovelock Black Holes

2008-01-01

['-', '-']

[]

Lovelock theory is a natural extension of Einstein theory of gravity to higher dimensions, and it is of great interest in theoretical physics as it describes a wide class of models. In particular, it describes string theory inspired ultraviolet corrections to Einstein-Hilbert action, while admits the Einstein general relativity and the so-called Chern-Simons theories of gravity as particular cases. Here, we give an introduction to the black hole solutions of Lovelock theory and analyze their most important properties. These solutions can be regarded as generalizations of the Boulware-Deser solution of Einstein-Gauss-Bonnet gravity, which we discuss in detail here. We briefly discuss some recent progress in understanding these and other solutions, like topological black holes that represent black branes of the theory, and vacuum thin-shell wormhole-like geometries that connect two different asymptotically de Sitter spaces. We also make some comments on solutions with time-like naked singularities.

[]

https://arxiv.org/pdf/0805.3575.pdf

1997A&A...318..673Y

Formation of MACHO-primordial black holes in inflationary cosmology.

1997-01-01

['cosmology theory', 'cosmology early universe', 'cosmology dark matter', 'black hole physics', 'astrophysics']

[]

As a nonbaryonic explanation of massive compact halo objects, a phenomenological model is presented which predicts formation of primordial black holes at a desired mass scale. The required feature of initial density fluctuation is realized making use of primordially isocurvature fluctuations generated in an inflationary universe model with multiple scalar fields.

[]

https://arxiv.org/pdf/astro-ph/9509027.pdf

2009JHEP...06..075M

Lifshitz topological black holes

2009-01-01

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

[]

I find a class of black hole solutions to a (3+1) dimensional theory gravity coupled to abelian gauge fields with negative cosmological constant that has been proposed as the dual theory to a Lifshitz theory describing critical phenomena in (2+1) dimensions. These black holes are all asymptotic to a Lifshitz fixed point geometry and depend on a single parameter that determines both their area (or size) and their charge. Most of the solutions are obtained numerically, but an exact solution is also obtained for a particular value of this parameter. The thermodynamic behaviour of large black holes is almost the same regardless of genus, but differs considerably for small black holes. Screening behaviour is exhibited in the dual theory for any genus, but the critical length at which it sets in is genus-dependent for small black holes.

[]

https://arxiv.org/pdf/0903.1136.pdf

2009ApJ...706L.215J

Massive Galaxies in COSMOS: Evolution of Black Hole Versus Bulge Mass but not Versus Total Stellar Mass Over the Last 9 Gyr?

2009-01-01

['galaxies active', 'galaxies evolution', 'galaxies fundamental parameters', 'galaxies nuclei', '-']

[]

We constrain the ratio of black hole (BH) mass to total stellar mass of type-1 active galactic nuclei (AGNs) in the COSMOS survey at 1 &lt; z &lt; 2. For 10 AGNs at mean redshift z ~ 1.4 with both Hubble Space Telescope (HST)/ACS and HST/NICMOS imaging data, we are able to compute the total stellar mass M <SUB>*,total</SUB>, based on rest-frame UV-to-optical host galaxy colors which constrain mass-to-light ratios. All objects have virial M <SUB>BH</SUB> estimates available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find within errors zero difference between the M <SUB>BH</SUB>-M <SUB>*,total</SUB> relation at z ~ 1.4 and the M <SUB>BH</SUB>-M <SUB>*,bulge</SUB> relation in the local universe. Our interpretation is (1) if our objects were purely bulge-dominated, the M <SUB>BH</SUB>-M <SUB>*,bulge</SUB> relation has not evolved since z ~ 1.4. However, (2) since we have evidence for substantial disk components, the bulges of massive galaxies (M <SUB>*,total</SUB> = 11.1 ± 0.3 or log M <SUB>BH</SUB> ~ 8.3 ± 0.2) must have grown over the last 9 Gyr predominantly by redistribution of the disk into the bulge mass. Since all necessary stellar mass exists in galaxies at z = 1.4, no star formation or addition of external stellar material is required, but only a redistribution, e.g., induced by minor and major merging or through disk instabilities. Merging, in addition to redistributing mass in the galaxy, will add both BH and stellar/bulge mass, but does not change the overall final M <SUB>BH</SUB>/M <SUB>*,bulge</SUB> ratio. Since the overall cosmic stellar and BH mass buildup trace each other tightly over time, our scenario of bulge formation in massive galaxies is independent of any strong BH feedback and means that the mechanism coupling BH and bulge mass until the present is very indirect. <P />Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555, the XMM-Newton telescope, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, the European Southern Observatory under Large Program 175.A-0839, the Magellan Telescope which is operated by the Carnegie Observatories, and the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

[]

https://arxiv.org/pdf/0907.5199.pdf

2007CQGra..24.5581B

Black hole mass and angular momentum in topologically massive gravity

2007-01-01

['-', '-']

[]

We extend the Abbott Deser Tekin approach to the computation of the Killing charge for a solution of topologically massive gravity (TMG) linearized around an arbitrary background. This is then applied to evaluate the mass and angular momentum of black hole solutions of TMG with non-constant curvature asymptotics. The resulting values, together with the appropriate black hole entropy, fit nicely into the first law of black hole thermodynamics.

[]

https://arxiv.org/pdf/0706.0263.pdf

2004PhRvL..92u1101B

Numerical Simulation of Orbiting Black Holes

2004-01-01

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

[]

We present numerical simulations of binary black hole systems which for the first time last for about one orbital period for close but still separate black holes as indicated by the absence of a common apparent horizon. An important part of the method is the construction of comoving coordinates, in which both the angular and the radial motion are minimized through a dynamically adjusted shift condition. We use fixed mesh refinement for computational efficiency.

[]

https://arxiv.org/pdf/gr-qc/0312112.pdf

2008PhRvA..78b1603B

Nonlocal density correlations as a signature of Hawking radiation from acoustic black holes

2008-01-01

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

[]

We have used the analogy between gravitational systems and nonhomogeneous fluid flows to calculate the density-density correlation function of an atomic Bose-Einstein condensate in the presence of an acoustic black hole. The emission of correlated pairs of phonons by Hawking-like process results into a peculiar long-range density correlation. Quantitative estimations of the effect are provided for realistic experimental configurations.

[]

https://arxiv.org/pdf/0711.4520.pdf

2020ApJ...900..100R

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

2020-01-01

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

[]

Hot spots, or plasmoids, which form due to magnetic reconnection in current sheets, are conjectured to power frequent X-ray and near-infrared flares from Sgr A*, the black hole in the center of our Galaxy. It is unclear how, where, and when current sheets form in black hole accretion disks. We perform axisymmetric general-relativistic resistive magnetohydrodynamics simulations to model reconnection and plasmoid formation in a range of accretion flows. Current sheets and plasmoids are ubiquitous features that form regardless of the initial magnetic field in the disk, the magnetization in the quasisteady-state phase of accretion, and the spin of the black hole. Within 10 Schwarzschild radii from the event horizon, we observe plasmoids forming, after which they can merge, grow to macroscopic scales of the order of a few Schwarzschild radii, and are ultimately advected along the jet's sheath or into the disk. Large plasmoids are energized to relativistic temperatures via reconnection and contribute to the jet's limb brightening. We find that only hot spots forming in magnetically arrested disks can potentially explain the energetics of Sgr A* flares. The flare period is determined by the reconnection rate, which we find to be between $0.01c$ and $0.03c$ in all cases, consistent with studies of reconnection in isolated Harris-type current sheets. We quantify magnetic dissipation and nonideal electric fields, which can efficiently inject nonthermal particles. We show that explicit resistivity allows for converged numerical solutions, such that the electromagnetic energy evolution and dissipation become independent of the grid scale for the extreme resolutions considered here.

[]

https://arxiv.org/pdf/2003.04330.pdf

2020PhRvD.101d4022E

Universal threshold for primordial black hole formation

2020-01-01

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

[]

In this paper, we argue and show numerically that the threshold to form primordial black holes from an initial spherically symmetric perturbation is, to an excellent approximation, universal, whenever given in terms of the compaction function averaged over a sphere of radius r<SUB>m</SUB>, where r<SUB>m</SUB> is the scale on which the compaction function is maximum. This can be understood as the requirement that, for a black hole to form, each shell of the averaged compaction function should have an amplitude exceeding the so-called Harada-Yoo-Kohri limit. For a radiation dominated universe we argued, supported by the numerical simulations, that this limit is δ<SUB>c</SUB>=0.40 , which is slightly below the one quoted in the literature. Additionally, we show that the profile dependence of the threshold for the compaction function is only sensitive to its curvature at the maximum. We use these results to provide an analytic formula for the threshold amplitude of the compaction function at its maximum in terms of the normalized compaction function curvature at r<SUB>m</SUB>.

[]

https://arxiv.org/pdf/1907.13311.pdf

2010IJTP...49.1649M

Semiclassical Loop Quantum Black Hole

2010-01-01

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

[]

In this paper we improve the semiclassical analysis of loop quantum black hole (LQBH) in the conservative approach of a constant polymeric parameter. In particular we focus our attention on the space-time structure. We introduce a very simple modification of the spherically symmetric Hamiltonian constraint in terms of holonomies. The new quantum constraint reduces to the classical constraint when the polymeric parameter δ goes to zero. Using this modification we obtain a large class of semiclassical solutions parametrized by a generic function σ( δ). We find that only a particular choice of this function reproduces the Schwarzschild black hole solution outside the black hole with the correct asymptotic flat limit. In r=0 the semiclassical metric is regular and the Kretschmann invariant has a maximum peaked at r <SUB>max </SUB> ∝ l <SUB> P </SUB>. The radial position of the peak does not depend on the black hole mass and the polymeric parameter δ. The semiclassical solution is very similar to the Reissner-Nordström metric. We construct the Carter-Penrose diagrams explicitly, giving a causal description of the space-time and its maximal extension. The LQBH metric interpolates between two asymptotically flat regions, the r→∞ region and the r→0 region. We study the thermodynamics of the semiclassical solution. The temperature, entropy and the evaporation process are regular and could be defined independently from the polymeric parameter δ. We study the particular metric when the polymeric parameter goes towards to zero. This metric is regular in r=0 and has only one event horizon in r=2 m. The radial position of the Kretschmann invariant maximum depends only on l <SUB> P </SUB>. As such the polymeric parameter δ does not play any role in the black hole singularity resolution. The thermodynamics is the same.

[]

https://arxiv.org/pdf/0811.2196.pdf

2018JHEP...03..044L

Inelastic black hole scattering from charged scalar amplitudes

2018-01-01

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

[]

We explain how the lowest-order classical gravitational radiation produced during the inelastic scattering of two Schwarzschild black holes in General Relativity can be obtained from a tree scattering amplitude in gauge theory coupled to scalar fields. The gauge calculation is related to gravity through the double copy. We remove unwanted scalar forces which can occur in the double copy by introducing a massless scalar in the gauge theory, which is treated as a ghost in the link to gravity. We hope these methods are a step towards a direct application of the double copy at higher orders in classical perturbation theory, with the potential to greatly streamline gravity calculations for phenomenological applications.

[]

https://arxiv.org/pdf/1711.03901.pdf

2011MNRAS.413.1479S

The Spitzer/IRAC view of black hole-bulge scaling relations

2011-01-01

['black hole physics', 'galaxies bulges', 'galaxies fundamental parameters', 'galaxies nuclei', 'galaxies photometry', 'astronomy infrared', '-']

[]

We present a mid-infrared investigation of the scaling relations between supermassive black hole masses (M<SUB>BH</SUB>) and the structural parameters of the host spheroids in local galaxies. This work is based on 2D bulge-disc decompositions of Spitzer/IRAC 3.6 μm images of 57 galaxies with M<SUB>BH</SUB> estimates. We first verify the accuracy of our decomposition by examining the Fundamental Plane (FP) of spheroids at 3.6 μm. Our estimates of effective radii (R<SUB>e</SUB>) and average surface brightnesses, combined with velocity dispersions from the literature, define a FP relation consistent with previous determinations but doubling the observed range in R<SUB>e</SUB>. None of our galaxies is an outlier of the FP, demonstrating the accuracy of our bulge-disc decomposition which also allows us to independently identify pseudo-bulges in our sample. We calibrate M/L at 3.6 μm by using the tight M<SUB>dyn</SUB>-L<SUB>bul</SUB> relation (∼0.1 dex intrinsic dispersion) and find that no colour corrections are required to estimate the stellar mass. The 3.6 μm luminosity is thus the best tracer of stellar mass yet studied. We then explore the connection between M<SUB>BH</SUB> and bulge structural parameters (luminosity, mass, effective radius). We find tight correlations of M<SUB>BH</SUB> with both 3.6 μm bulge luminosity and dynamical mass (M<SUB>BH</SUB>/M<SUB>dyn</SUB>∼ 1/1000), with intrinsic dispersions of ∼0.35 dex, similar to the M<SUB>BH</SUB>-σ relation. Our results are consistent with previous determinations at shorter wavelengths. By using our calibrated M/L, we rescale M<SUB>BH</SUB>-L<SUB>bul</SUB> to obtain the M<SUB>BH</SUB>-M<SUB>★</SUB> relation, which can be used as the local reference for high-z studies which probe the cosmic evolution of M<SUB>BH</SUB>-galaxy relations and where the stellar mass is inferred directly from luminosity measurements. The analysis of pseudo-bulges shows that four out of nine lie on the scaling relations within the observed scatter, while those with small M<SUB>BH</SUB> are significantly displaced. We explore the different origins for such behaviour while considering the possibility of nuclear morphological components not reproduced by our 2D decomposition.

[]

https://arxiv.org/pdf/1012.3073.pdf

2012MNRAS.423L..55T

Prograde and retrograde black holes: whose jet is more powerful?

2012-01-01

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

[]

The outflow efficiency (η) from black hole (BH) accretion disc systems is known to depend upon both the BH spin (a) and the amount of large-scale magnetic flux threading the BH and disc. Semi-analytical flux-trapping models suggest retrograde BHs should trap much more large-scale magnetic flux near the BH leading to much higher η than for prograde BHs. We self-consistently determine the amount of large-scale magnetic flux trapped by rapidly spinning (a=-0.9 and 0.9) BHs using global 3D time-dependent non-radiative general relativistic magnetohydrodynamic simulations of thick (h/r≈ 0.3-0.6) discs. We find that BH-trapped flux builds up until it is strong enough to disrupt the inner accretion disc. Contrary to prior flux-trapping models, which do not include the back-reaction of magnetic flux on the disc, our simulations show prograde BHs trap more magnetic flux, leading to about three times higher η than retrograde BHs for |a|= 0.9. Both spin orientations can produce highly efficient jets, η∼ 100 per cent, with increasing η for increasing disc thickness. The similarity of η for prograde and retrograde BHs makes it challenging to infer the sign of a based on jet energetics alone.

[]

https://arxiv.org/pdf/1201.4385.pdf

2013PhRvD..87j3506L

Gauge field production in supergravity inflation: Local non-Gaussianity and primordial black holes

2013-01-01

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

[]

When inflation is driven by a pseudoscalar field χ coupled to vectors as (α)/(4)χFF∼, this coupling may lead to a copious production of gauge quanta, which in turns induces non-Gaussian and non-scale-invariant corrections to curvature perturbations. We point out that this mechanism is generically at work in a broad class of inflationary models in supergravity, hence providing them with a rich set of observational predictions. When the gauge fields are massless, significant effects on cosmic microwave background scales emerge only for relatively large α. We show that in this regime, the curvature perturbations produced at the last stages of inflation have a relatively large amplitude that is of the order of the upper bound set by the possible production of primordial black holes by non-Gaussian perturbations. On the other hand, within the supergravity framework described in our paper, the gauge fields can often acquire a mass through a coupling to additional light scalar fields. Perturbations of these fields modulate the duration of inflation, which serves as a source for non-Gaussian perturbations of the metric. In this regime, the bounds from primordial black holes are parametrically satisfied and non-Gaussianity of the local type can be generated at the observationally interesting level f<SUB>NL</SUB>∼O(10).

[]

https://arxiv.org/pdf/1212.1693.pdf