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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Resolving black-hole microstructure with new momentum carriers

All known horizonless black-hole microstate geometries correspond to brane sources that acquire a finite size, and hence break the spherical symmetry of the black hole. We construct, for the first time, solutions with zero horizon area that have the same charges as a three-charge F1-NS5-P Type-IIA black hole and preserve this spherical symmetry. The momentum of these solutions is carried by longitudinal D0-D4 density fluctuations inside the NS5-branes. We argue that these solutions should be interpreted as the long-throat limit of a family of smooth, horizonless microstate geometries, called superstrata, where such geometries degenerate. The existence of these geometries indicates that a finite-size horizon does not appear even in the singular corners of the moduli space of three-charge microstate geometries.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ON THE ORIENTATION AND MAGNITUDE OF THE BLACK HOLE SPIN IN GALACTIC NUCLEI

Massive black holes (BHs) in galactic nuclei vary their mass M {sub BH} and spin vector J {sub BH} due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e., when the accretion episodes are randomly and isotropically oriented, or coherent, i.e., when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the BH growth evolving contemporarily with mass, spin modulus a, and spin direction. We discover the occurrence of two regimes. An early phase (M {sub BH} {approx}< 10{sup 7} M {sub Sun }) in which rapid alignment of the BH spin direction to the disk angular momentum in each single episode leads to erratic changes in the BH spin orientation and at the same time to large spins (a {approx} 0.8). A second phase starts when the BH mass increases above {approx}> 10{sup 7} M {sub Sun} and the accretion disks carry less mass and angular momentum relative to the hole. In the absence of a preferential direction, the BHs tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the BH spin can increase up to a {approx} 1 for very massive black holes (M {sub BH} {approx}> 10{sup 8} M {sub Sun }), and its direction is stable over the many accretion cycles. We discuss the implications of our results in the realm of the observations of BH spin and jet orientations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ON THE SIZE AND LOCATION OF THE X-RAY EMITTING CORONAE AROUND BLACK HOLES

The observation of energetic X-ray emission from black holes, inconsistent with thermal emission from an accretion disk, has long indicated the presence of a ''corona'' around these objects. However, our knowledge of the geometry, composition, and processes within black hole coronae is severely lacking. Basic questions regarding their size and location are still a topic of debate. In this Letter, we show that for black holes with luminosities L {approx}> 10{sup -2} L{sub Edd}-characteristic of many Seyferts, quasars, and stellar-mass black holes (in their brighter states)-advanced imaging and timing data strongly favor X-ray emitting regions that are highly compact, and only a few Gravitational radii above the accretion disk. The inclusion of a large number of possible systematics uncertainties does not significantly change this conclusion with our results still suggesting emission from within {approx}20r{sub g} in all cases. This result favors coronal models wherein most of the hard X-ray emission derives from magnetic reconnection in the innermost disk and/or from processes in the compact base of a central, relativistic jet.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2008

Binary Black Hole Mergers, Gravitational Waves, and LISA

The final merger of comparable mass binary black holes is expected to be the strongest source of gravitational waves for LISA. Since these mergers take place in regions of extreme gravity, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms. For more than 30 years, scientists have tried to compute black hole mergers using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. Within the past few years, however, this situation has changed dramatically, with a series of remarkable breakthroughs. We will present the results of new simulations of black hole mergers with unequal masses and spins, focusing on the gravitational waves emitted and the accompanying astrophysical "kicks." The magnitude of these kicks has bearing on the production and growth of supermassive black holes during the epoch of structure formation, and on the retention of black holes in stellar clusters.

Centrella, Joan↗
DOE OSTI2016

Cosmic censorship of rotating Anti-de Sitter black hole

We test the validity of cosmic censorship in the rotating anti-de Sitter black hole. For this purpose, we investigate whether the extremal black hole can be overspun by the particle absorption. The particle absorption will change the mass and angular momentum of the black hole, which is analyzed using the Hamilton-Jacobi equations consistent with the laws of thermodynamics. We have found that the mass of the extremal black hole increases more than the angular momentum. Therefore, the outer horizon of the black hole still exists, and cosmic censorship is valid.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A RAPIDLY SPINNING BLACK HOLE POWERS THE EINSTEIN CROSS

Observations over the past 20 yr have revealed a strong relationship between the properties of the supermassive black hole lying at the center of a galaxy and the host galaxy itself. The magnitude of the spin of the black hole will play a key role in determining the nature of this relationship. To date, direct estimates of black hole spin have been restricted to the local universe. Herein, we present the results of an analysis of ∼0.5 Ms of archival Chandra observations of the gravitationally lensed quasar Q 2237+305 (aka the {sup E}instein-cross{sup )}, lying at a redshift of z = 1.695. The boost in flux provided by the gravitational lens allows constraints to be placed on the spin of a black hole at such high redshift for the first time. Utilizing state of the art relativistic disk reflection models, the black hole is found to have a spin of a{sub ∗}=0.74{sub −0.03}{sup +0.06} at the 90% confidence level. Placing a lower limit on the spin, we find a {sub *} ≥ 0.65 (4σ). The high value of the spin for the ∼10{sup 9} M {sub ☉} black hole in Q 2237+305 lends further support to the coherent accretion scenario for black hole growth. This is the most distant black hole for which the spin has been directly constrained to date.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Systematic Biases in Parameter Estimation of Binary Black-Hole Mergers

Parameter estimation of binary-black-hole merger events in gravitational-wave data relies on matched filtering techniques, which, in turn, depend on accurate model waveforms. Here we characterize the systematic biases introduced in measuring astrophysical parameters of binary black holes by applying the currently most accurate effective-one-body templates to simulated data containing non-spinning numerical-relativity waveforms. For advanced ground-based detectors, we find that the systematic biases are well within the statistical error for realistic signal-to-noise ratios (SNR). These biases grow to be comparable to the statistical errors at high signal-to-noise ratios for ground-based instruments (SNR approximately 50) but never dominate the error budget. At the much larger signal-to-noise ratios expected for space-based detectors, these biases will become large compared to the statistical errors but are small enough (at most a few percent in the black-hole masses) that we expect they should not affect broad astrophysical conclusions that may be drawn from the data.

Littenberg, Tyson B.↗
DOE OSTI2016

Black holes and gravitational waves in models of minicharged dark matter

In viable models of minicharged dark matter, astrophysical black holes might be charged under a hidden U(1) symmetry and are formally described by the same Kerr-Newman solution of Einstein-Maxwell theory. These objects are unique probes of minicharged dark matter and dark photons. We show that the recent gravitational-wave detection of a binary black-hole coalescence by aLIGO provides various observational bounds on the black hole’s charge, regardless of its nature. The pre-merger inspiral phase can be used to constrain the dipolar emission of (ordinary and dark) photons, whereas the detection of the quasinormal modes set an upper limit on the final black hole’s charge. By using a toy model of a point charge plunging into a Reissner-Nordstrom black hole, we also show that in dynamical processes the (hidden) electromagnetic quasinormal modes of the final object are excited to considerable amplitude in the gravitational-wave spectrum only when the black hole is nearly extremal. The coalescence produces a burst of low-frequency dark photons which might provide a possible electromagnetic counterpart to black-hole mergers in these scenarios.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Unveiling the First Black Holes With JWST:Multi-wavelength Spectral Predictions

Growing supermassive black holes (∼10{sup 9} M{sub ⊙}) that power luminous z>6 quasars from light seeds—the remnants of the first stars—within a Gyr of the Big Bang poses a timing challenge. The formation of massive black hole seeds via direct collapse with initial masses ∼10{sup 4}--10{sup 5} M{sub ⊙} alleviates this problem. Viable direct-collapse black hole formation sites, the satellite halos of star-forming galaxies, merge and acquire stars to produce a new, transient class of high-redshift objects, obese black hole galaxies (OBGs). The accretion luminosity outshines that of the stars in OBGs. We predict the multi-wavelength energy output of OBGs and growing Pop III remnants at z = 9 for standard and slim disk accretion, as well as high and low metallicities of the associated stellar population. We derive robust selection criteria for OBGs—a pre-selection to eliminate blue sources, followed by color–color cuts ([F{sub 090W}−F{sub 220W}]>0;−0.3<[F{sub 200W}−F{sub 444W}]<0.3) and the ratio of X-ray flux to rest-frame optical flux (F{sub X}/F{sub 444W}≫1). Our cuts sift out OBGs from other bright, high- and low-redshift contaminants in the infrared. OBGs with predicted M{sub AB}<25 are unambiguously detectable by the Mid-Infrared Instrument (MIRI), on the upcoming James Webb Space Telescope (JWST). For parameters explored here, growing Pop III remnants with predicted M{sub AB}<30 will likely be undetectable by JWST. We demonstrate that JWST has the power to discriminate between initial seeding mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Superradiance and black hole bomb in five-dimensional minimal ungauged supergravity

We examine the black hole bomb model which consists of a rotating black hole of five-dimenensional minimal ungauged supergravity and a reflecting mirror around it. For low-frequency scalar perturbations, we find solutions to the Klein-Gordon equation in the near-horizon and far regions of the black hole spacetime. To avoid solutions with logarithmic terms, we assume that the orbital quantum number l takes on nearly, but not exactly, integer values and perform the matching of these solutions in an intermediate region. This allows us to calculate analytically the frequency spectrum of quasinormal modes, taking the limits as l approaches even or odd integers separately. We find that all l modes of scalar perturbations undergo negative damping in the regime of superradiance, resulting in exponential growth of their amplitudes. Thus, the model under consideration would exhibit the superradiant instability, eventually behaving as a black hole bomb in five dimensions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole

Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the Walker–Penrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Dual dressed black holes as the end point of the charged superradiant instability in $\mathcal{N} = 4$ Yang Mills

Charged Black holes in AdS_5 × S^5 A d S 5 × S 5 suffer from superradiant instabilities over a range of energies. Hairy black hole solutions (constructed within gauged supergravity) have previously been proposed as endpoints to this instability. We demonstrate that these hairy black holes are themselves unstable to the emission of large dual giant gravitons. We propose that the endpoint to this instability is given by Dual Dressed Black Holes (DDBH)s; configurations consisting of one, two, or three very large dual giant gravitons surrounding a core AdS A d S black hole with one, two, or three SO(6) S O ( 6 ) chemical potentials equal to unity. The dual giants each live at AdS A d S radial coordinates of order \sqrt{N} N and each carry charge of order N^2 N 2 . The large separation makes DDBHs a very weakly interacting mix of their components and allows for a simple computation of their thermodynamics. We conjecture that DDBHs dominate the phase diagram of \mathcal{N}=4 𝒩 = 4 Yang-Mills over a range of energies around the BPS plane, and provide an explicit construction of this phase diagram, briefly discussing the interplay with supersymmetry. We develop the quantum description of dual giants around black hole backgrounds and explicitly verify that DDBHs are stable to potential tunneling instabilities, precisely when the chemical potentials of the core black holes equal unity. We also construct the 10-dimensional DDBH bulk solutions.

Choi, Sunjin (ORCID:0000000283310199)↗
DOE OSTI2024

Runaway Eccentricity Growth: A Pathway for Binary Black Hole Mergers in AGN Disks

Binary black holes (BBHs) embedded within the accretion disks that fuel active galactic nuclei (AGN) are promising progenitors for the source of gravitational wave (GW) events detected by LIGO/VIRGO. Several recent studies have shown that when these binaries form, they are likely to be highly eccentric and retrograde. However, many uncertainties remain concerning the orbital evolution of these binaries as they either inspiral toward merger or disassociate. Previous hydrodynamical simulations exploring their orbital evolution have been predominantly two-dimensional or have been restricted to binaries on nearly circular orbits. We present the first high-resolution, three-dimensional local shearing-box simulations of both prograde and retrograde eccentric BBHs embedded in AGN disks. We find that retrograde binaries shrink several times faster than their prograde counterparts and exhibit significant orbital eccentricity growth, the rate of which monotonically increases with binary eccentricity. Our results suggest that retrograde binaries may experience runaway orbital eccentricity growth, which may bring them close enough together at pericenter for GW emission to drive them to coalescence. Although their eccentricity is damped, prograde binaries shrink much faster than their orbital eccentricity decays, suggesting they should remain modestly eccentric as they contract toward merger. Finally, binary precession driven by the AGN disk may dominate over precession induced by the supermassive black hole depending on the binary accretion rate and its location in the AGN disk, which can subdue the evection resonance and von Ziepel–Lidov–Kozai cycles.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Active galactic nuclei. IV - Supplying black hole clusters by tidal disruption and by tidal capture of stars

The extent to which individual holes in a cluster of black holes with a mass spectrum can liberate and accrete the resulting material by tidally disrupting stars they encounter, or by capturing stars as binary companions is studied. It is found that the smaller black holes in 'the halo' of such clusters can adequately supply themselves to the level M-dot sub h or greater than 0.0001(M-dot sub h) sub crit, and up to 0.05(M-dot sub h)sub crit for the smallest holes, by tidal disruption, as long as the cluster is embedded in a distribution of stars of relatively high density (not less than 0.1M sub cl/cu pc), and as long as the entire cluster of stars is not too compact (not less than 0.5 pc). Consideration is given to modifications this 'internal' mode of supply introduces in the spectrum emitted by such black hole clusters, and to the current status of their viability as models for AGN and QSOs in light of dynamical studies by Quinlan and Shapiro (1987, 1989).

Stoeger, W. R.↗
DOE OSTI2019

Dark radiation and superheavy dark matter from black hole domination

If even a relatively small number of black holes were created in the early universe, they will constitute an increasingly large fraction of the total energy density as space expands. It is thus well-motivated to consider scenarios in which the early universe included an era in which primordial black holes dominated the total energy density. Within this context, we consider Hawking radiation as a mechanism to produce both dark radiation and dark matter. If the early universe included a black hole dominated era, we find that Hawking radiation will produce dark radiation at a level $\Delta N_{\rm eff} \sim 0.03-0.2$ for each light and decoupled species of spin 0, 1/2, or 1. This range is well suited to relax the tension among late and early-time Hubble determinations, and is within the reach of upcoming CMB experiments. The dark matter could additionally originate as Hawking radiation in a black hole dominated early universe, although such dark matter candidates must be very heavy ($m_{\rm DM} >10^{11}$ GeV) if they are to avoid exceeding the measured abundance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2007

Binary Black Holes, Gravitational Waves, and Numerical Relativity

Massive black hole (MBH) binaries are found at the centers of most galaxies. MBH mergers trace galaxy mergers and are strong sources of gravitational waves. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of very strong gravitational fields, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms. For more than 30 years, scientists have tried to compute these waveforms using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities. causing them to crash well before the black hole:, in the binary could complete even a single orbit. Recently this situation has changed dramatically, with a series of amazing breakthroughs. This presentation shows how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers. Focus is on the recent advances that that reveal these waveforms, and the potential for discoveries that arises when these sources are observed by LIGO and LISA.

Centrella, Joan↗
DOE OSTI2017

Minidisks in Binary Black Hole Accretion

Newtonian simulations have demonstrated that accretion onto binary black holes produces accretion disks around each black hole (“minidisks”), fed by gas streams flowing through the circumbinary cavity from the surrounding circumbinary disk. We study the dynamics and radiation of an individual black hole minidisk using 2D hydrodynamical simulations performed with a new general relativistic version of the moving-mesh code Disco. We introduce a comoving energy variable that enables highly accurate integration of these high Mach number flows. Tidally induced spiral shock waves are excited in the disk and propagate through the innermost stable circular orbit, providing a Reynolds stress that causes efficient accretion by purely hydrodynamic means and producing a radiative signature brighter in hard X-rays than the Novikov–Thorne model. Disk cooling is provided by a local blackbody prescription that allows the disk to evolve self-consistently to a temperature profile where hydrodynamic heating is balanced by radiative cooling. We find that the spiral shock structure is in agreement with the relativistic dispersion relation for tightly wound linear waves. We measure the shock-induced dissipation and find outward angular momentum transport corresponding to an effective alpha parameter of order 0.01. We perform ray-tracing image calculations from the simulations to produce theoretical minidisk spectra and viewing-angle-dependent images for comparison with observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Fatal youth of the Universe: black hole threat for the electroweak vacuum during preheating

Small evaporating black holes were proposed to be dangerous inducing fast decay of the electroweak false vacuum. We observe that the flat-spectrum matter perturbations growing at the post-inflationary matter dominated stage can produce such black holes in a tiny amount which may nevertheless be sufficient to destroy the vacuum in the visible part of the Universe via the induced process. If the decay probability in the vicinity of Planck-mass black holes was of order one as suggested in literature, the absence of such objects in the early Universe would put severe constraints on inflation and subsequent stages thus excluding many well-motivated models (e.g. the R {sup 2}-inflation) and supporting the need of new physics in the Higgs sector. We give a qualitative argument, however, that exponential suppression of the probability should persist in the limit of small black hole masses. This suppression relaxes our cosmological constraints, and, if sufficiently strong, may cancel them.

79 ASTRONOMY AND ASTROPHYSICS↗