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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

AdS 5 black hole entropy near the BPS limit

We analyze AdS 5 black holes that are nearly supersymmetric. They depart from the BPS limit in two distinct ways: a temperature takes them above extremality and a potential maintains extremality but violates a certain constraint. We study the thermodynamics of these deformations and their interplay in detail. We discuss recent microscopic computations of BPS black hole entropy in N = 4 SYM and generalize the arguments to the nearBPS regime by relaxing constraints imposed by supersymmetry. Our methods recover gravitational results from microscopic theory also for nearBPS black holes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Black hole cannibalism

Here, we consider a version of the Hayden–Preskill thought experiment in which the message thrown into the black hole is itself a smaller black hole. We then discuss the implications of the existence of a recovery channel for this black hole message at asymptotic infinity, resulting in a sharpening of the black hole information paradox for observers who never need to approach a horizon. We suggest decoherence mechanisms as a way of resolving this sharpened paradox.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Black Hole Formation Accompanied by the Supernova Explosion of a 40 M ⊙ Progenitor Star

Abstract We have simulated the collapse and evolution of the core of a solar-metallicity 40 M ⊙ star and find that it explodes vigorously by the neutrino mechanism, despite its very high “compactness.” Within ∼1.5 s of explosion, a black hole forms. The explosion is very asymmetrical and has a total explosion energy of ∼1.6 × 10 51 erg. At black hole formation, its baryon mass is ∼2.434 M ⊙ and gravitational mass is 2.286 M ⊙ . Seven seconds after black hole formation, an additional ∼0.2 M ⊙ is accreted, leaving a black hole baryon mass of ∼2.63 M ⊙ . A disk forms around the proto−neutron star, from which a pair of neutrino-driven jets emanates. These jets accelerate some of the matter up to speeds of ∼45,000 km s −1 and contain matter with entropies of ∼50. The large spatial asymmetry in the explosion results in a residual black hole recoil speed of ∼1000 km s −1 . This novel black hole formation channel now joins the other black hole formation channel between ∼12 and ∼15 M ⊙ discovered previously and implies that the black hole/neutron star birth ratio for solar-metallicity stars could be ∼20%. However, one channel leaves black holes in perhaps the ∼5–15 M ⊙ range with low kick speeds, while the other leaves black holes in perhaps the ∼2.5–3.0 M ⊙ mass range with high kick speeds. However, even ∼8.8 s after core bounce the newly formed black hole is still accreting at a rate of ∼2 × 10 −2 M ⊙ s −1 , and whether the black hole eventually achieves a significantly larger mass over time is yet to be determined.

Astronomy & Astrophysics↗
DOE OSTI2020

From microscopic black hole entropy toward Hawking radiationc

The AdS/CFT correspondence has recently provided a novel approach for counting the microstates of black holes impressively matching the macroscopic Bekenstein–Hawking entropy formula of rotating electrically charged asymptotically AdS black holes in four to seven dimensions. This approach is designed for supersymmetric extremal black holes, but can also be extended to nonsupersymmetric, near-extremal black holes. Besides the dual higher-dimensional boundary CFT, an effective 2D CFT emerges in a certain near-horizon limit accounting for both the extremal and the near-extremal black hole entropies. Furthermore, this effective 2D description is universal across dimensions and comes naturally equipped with an approach to quantitatively tackle aspects of Hawking radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

GW190412: Observation of a binary-black-hole coalescence with asymmetric masses

We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO's and Virgo's third observing run. The signal was recorded on April 12, 2019 at 05:30:44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: A ~30 M ⊙ black hole merged with a ~8 M ⊙ black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed on GW190412 indicates consistency with Einstein's general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Perturbations of Gibbons-Maeda black holes in Einstein-Maxwell-dilaton theories

The study of perturbations around black hole backgrounds in general relativity and Einstein-Maxwell theory has a long history, going back to the work of Regge and Wheeler in the 1950s. As part of a broader investigation of perturbations around black holes in supergravity, we describe here our results for the perturbations around the Gibbons-Maeda static charged black holes in a class of Einstein-Maxwell-Dilaton theories. Our analysis follows the general strategy developed by Chandrasekhar and Xanthopoulos for the perturbations of the Reissner-Nordström black hole. Here, the analysis is considerably more involved, because of the presence of the dilaton field, which couples to the other polar modes. We nonetheless find that the problem is completely solvable, in the sense that one can separate variables and eventually describe all the perturbations in terms of diagonalised second-order radial equations. We are able to prove the mode stability of all the Gibbons-Maeda black hole solutions. Published by the American Physical Society 2024

Pope, C. N. (ORCID:0000000284012564)↗
DOE OSTI2024

Gravitational waves from primordial black hole evaporation with large extra dimensions

Abstract The spectra of gravitational waves from black hole evaporation generically peak at frequencies of order the Hawking temperature, making this signal ultra-high frequency for primordial black holes evaporating in the early universe. This motivates us to consider small black holes in theories with large extra dimensions, for which the peak frequency can be lowered substantially, since the true bulk Planck scaleM * can be much smaller than the effectiveM Pl . We study the emission of brane-localized gravitons during the Hawking evaporation of ultra-light primordial black holes in the context of theories with large extra dimensions, with the ultimate goal of computing the contribution to the stochastic gravitational wave background. To accurately model black hole evolution, we compute greybody factors for particles of spin-0, 1/2, 1, and 2 emitted on the brane and in the bulk, presuming the majority of emission proceeds during the Schwarzschild phase. We then compute the power spectrum and present day spectral density parameter for brane-localized gravitons contributing to a gravitational wave signal. We find that for an optimal choice of parameters, the peak frequency plateaus in the sub-MHz regime, within range of planned high-frequency gravitational wave detectors, making this scenario a target for detection once their sensitivity exceeds ΔN eff bounds.

Astronomy & Astrophysics↗
NASA NTRS1989

The signature of a black hole transit

This paper considers the possibility of identifying a black hole on the basis of the detection of some unique effect occurring during the transit of a black hole across the stellar disk of a companion star in a binary system. The results of Monte-Carlo calculations show that the amplitude of the photometric and polarimetric light curves in a typical X-ray binary is too small to be observed with present instrumentation, but that a black hole transit might be detectable in a binary having a large separation of the components. No binary system suggested as containing a stellar-mass-sized black hole is a like candidate to exhibit an observable transit signature, with the possible exception of X Persei/4U0352+30 described by White et al. (1976).

Dolan, Joseph F.↗
DOE OSTI2024

Random Circuits in the Black Hole Interior

In this paper, we present a quantitative holographic relation between a microscopic measure of randomness and the geometric length of the wormhole in the black hole interior. To this end, we perturb an AdS black hole with Brownian semiclassical sources, implementing the continuous version of a random quantum circuit for the black hole. We use the random circuit to prepare ensembles of states of the black hole whose semiclassical duals contain Einstein-Rosen (ER) caterpillars: long cylindrical wormholes with large numbers of matter inhomogeneities, of linearly growing length with the circuit time. In this setup, we show semiclassically that the ensemble of ER caterpillars of average length $k\ell_Δ$ and matter correlation scale $\ell_Δ$ forms an approximate quantum state $k$-design of the black hole. At exponentially long circuit times, the ensemble of ER caterpillars becomes polynomial-copy indistinguishable from a collection of random states of the black hole. We comment on the implications of these results for holographic circuit complexity and for the holographic description of the black hole interior.

FOS: Physical sciences↗
DOE OSTI2024

Kerr black hole evaporation and Page curve

In this paper, we compute the black hole entropy and the entanglement entropy of Hawking radiations due to photons during the evaporation of a 4D asymptotically flat Kerr black hole. The Page curve for the Kerr black hole is obtained in the original way à la Page, and it qualitatively mimics the curve for the Schwarzschild black hole but has some new features.

Astronomy & Astrophysics↗
DOE OSTI2022

BASS. XXXVI. Constraining the Local Supermassive Black Hole–Halo Connection with BASS DR2 AGNs

We investigate the connection between supermassive black holes (SMBHs) and their host dark matter halos in the local universe using the clustering statistics and luminosity function of active galactic nuclei (AGNs) from the Swift/BAT AGN Spectroscopic Survey (BASS DR2). By forward-modeling AGN activity into snapshot halo catalogs from N -body simulations, we test a scenario in which SMBH mass correlates with dark matter (sub)halo mass for fixed stellar mass. We compare this to a model absent of this correlation, where stellar mass alone determines the SMBH mass. We find that while both simple models are able to largely reproduce the abundance and overall clustering of AGNs, the model in which black hole mass is tightly correlated with halo mass is preferred by the data by 1.8 σ . When including an independent measurement on the black hole mass–halo mass correlation, this model is preferred by 4.6 σ . We show that the clustering trends with black hole mass can further break the degeneracies between the two scenarios and that our preferred model reproduces the measured clustering differences on one-halo scales between large and small black hole masses. These results indicate that the halo binding energy is fundamentally connected to the growth of SMBHs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

An effective field theory of quantum mechanical black hole horizons

We develop an effective theory which describes black holes with quantum mechanical horizons that is valid at scales long compared to the Schwarzschild radius but short compared to the lifetime of the black hole. Our formalism allows one to calculate the quantum mechanical effects in scattering processes involving black hole asymptotic states. We point out that the EFT Wightman functions which describe Hawking radiation in the Unruh vacuum are not Planck suppressed and are actually enhanced relative to those in the Boulware vacuum, for which such radiation is absent. We elaborate on this point showing how the non-Planck suppressed effects of Hawking radiation cancel in classical observables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2020

GW190412: Observation of a binary-black-hole coalescence with asymmetric masses

We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO’s and Virgo’s third observing run. The signal was recorded on April 12, 2019 at05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a∼30M⊙black hole merged with a ∼8M⊙black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed onGW190412 indicates consistency with Einstein’s general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.

R. Abbott↗
DOE OSTI2023

Primordial gravitational waves from black hole evaporation in standard and nonstandard cosmologies

Gravitons radiated from light, evaporating black holes contribute to the stochastic background of gravitational waves. The spectrum of such emission depends on both the mass and the spin of the black holes, as well as on the redshifting that occurs between the black hole formation and today. This, in turn, depends on the expansion history of the Universe, which is largely unknown and unconstrained at times prior to the synthesis of light elements. Here, we explore the features of the stochastic background of gravitational waves from black hole evaporation under a broad range of possible early cosmological histories. The resulting gravitational wave signals typically peak at very high frequencies, and offer opportunities for proposed ultrahigh-frequency gravitational wave detectors. Lower-frequency peaks are also possible, albeit with a suppressed intensity that is likely well below the threshold of detectability. We find that the largest intensity peaks correspond to cosmologies dominated by fluids with equations of state that have large pressure-to-density ratios. Such scenarios can be constrained on the basis of violation of Δ⁢N eff bounds.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

An Extreme X-ray Disk Wind in the Black Hole Candidate IGR J17091-3624

Chandra spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk-dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized. dense. and to have typical velocities of approx 1000 km/s or less projected along our line of sight. Here. we present an analysis of two Chandra High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091-3624 and contemporaneous EVLA radio observations. obtained in 2011. The second Chandra observation reveals an absorption line at 6.91+/-0.01 keV; associating this line with He-like Fe XXV requires a blue-shift of 9300(+500/-400) km/ s (0.03c. or the escape velocity at 1000 R(sub schw)). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of approx 14600 km/s (0.05c), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091-3624 may originate within 43,300 Schwarzschild radii of the black hole, and may be expelling more gas than accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our Chandra observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems

King, A. L.↗
DOE OSTI2020

Black hole spin in X-ray binaries: giving uncertainties an $\mathcal{f}$

The two established techniques for measuring black hole spin in X-ray binaries often yield conflicting results, which must be resolved before either method may be deemed robust. In practice, black hole spin measurements based on fitting the accretion disc continuum effectively do not marginalize over the colour-correction factor f col . This factor parametrizes spectral hardening of the disc continuum by the disc atmosphere, whose true properties are poorly constrained. We incorporate reasonable systematic uncertainties in f col into the eight (non-maximal) black hole spin measurements vetted by the disc continuum fitting community. In most cases, an f col uncertainty of ±0.2–0.3 dominates the black hole spin error budget. We go on to demonstrate that plausible departures in f col values from those adopted by the disc continuum fitting practitioners can bring the discrepant black hole spins into agreement with those from iron line modelling. Systematic uncertainties in f col , such as the effects of strong magnetization, should be better understood before dismissing their potentially dominant impact on the black hole spin error budget.

4U 1543–47↗
DOE OSTI2025

Multifrequency Models of Black Hole Photon Rings from Low-luminosity Accretion Disks

Images of black holes encode both astrophysical and gravitational properties. Detecting highly lensed features in images can differentiate between these two effects. We present an accretion disk emission model coupled to the Adaptive Analytical Ray Tracing (AART) code that allows a fast parameter space exploration of black hole photon ring images produced from synchrotron emission from 10 to 670 GHz. As an application, we systematically study several disk models and compute their total flux density, average radii, and optical depth. The model parameters are chosen around fiducial values calibrated to general relativistic magnetohydrodynamic (GRMHD) simulations and observations of M87*. For the parameter space studied, we characterize the transition between optically thin and thick regimes and the frequency at which the first photon ring is observable. Our results highlight the need for careful definitions of photon ring radius in the image domain, as in certain models the highly lensed photon ring is dimmer than the direct emission at certain angles. We find that at low frequencies the ring radii are set by the electron temperature, while at higher frequencies the magnetic field strength plays a more significant role, demonstrating how multifrequency analysis can also be used to infer plasma parameters. Lastly, we show how our implementation can qualitatively reproduce multifrequency black hole images from GRMHD simulations when adding time variability to our disk model through Gaussian random fields. This approach provides a new method for simulating observations from the Event Horizon Telescope and the proposed Black Hole Explorer space mission.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Physics-Based Spectra of Accretion Disks around Black Holes

The purpose of this grant was to begin the process of deriving the light output of accretion disks around black holes directly from the actual processes that inject heat into the accreting matter, rather than from guessed dependences of heating rate on physical parameters. At JHU, the effort has focussed so far on models of accretion onto "intermediate mass black holes", a possible class of black holes, examples of which may have recently been discovered in nearby galaxies. There, Krolik and his student (Yawei Hui) have computed stellar atmospheres for uniformly-heated disks around this class of black holes. Their models serve two purposes: they are the very first serious attempts to compute the spectrum from accreting black holes in this mass range; and a library of such models can be used later in this program as contrasts for those computed on the basis of real disk dynamics. The output from these local disk calculations has also been successfully coupled to a program that applies the appropriate relativistic transformations and computes photon trajectories in order to predict the spectrum received by observers located at different polar angles. The principal new result of these calculations is the discovery of potentially observable ionization edges of H-like C and O at frequencies near the peak in flux from these objects. Most of the grant money at UCSB was spent on supporting graduate student Shane Davis. In addition. some money was spent on supporting two other students: Ari Socrates (now a Hubble Fellow at Princeton), and Laura Melling. Davis spent the year constructing stellar atmosphere models of accretion disks appropriate for the high/soft (thermal) state of black hole X-ray binaries. As with AGN models published previously by our collaboration with NASA support. our models include a complete general relativistic treatment of both the disk structure and the propagation of photons from the disk to a distant observer. They also include all important continuum opacity sources, including Compton scattering and bound-free opacity from abundant metal species. The principal new result is that bound-free opacity is very significant in altering the continuum spectral shape, resulting for example in quite different "color correction factors" compared to those predicted previously. In addition, the models predict a relationship between luminosity and inner disk temperature that is, for the first time, in accord with that observed. The primary purpose of the grant was to incorporate more realistic accretion disk physics, learned largely from simulations, into such spectral models. The Davis et al. paper includes consideration of a vertical dissipation profile computed from radiation magneto-hydrodynamic simulations of MRI turbulence by N. J. Turner (2004). So long as the disk is effectively thick, such dissipation profiles do not affect the predicted spectrum significantly. (More work needs to be done on these simulations, however.) A potentially more serious issue is that MRI turbulence produces substantial inhomogeneities, as do photon bubble instabilities. These inhomogeneities can affect the spectra by enhancing the effects of absorption opacity over scattering opacity. We have done some preliminary Monte Carlo calculations to explore these effects.

Krolik, Julian H.↗