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A model is presented in which both Fanaroff and Riley class I and II extragalactic jets are produced by magnetized accretion disk coronae in the ergospheres of rotating black holes.
We report that the formation of ultra rare supermassive black holes (SMBHs), with masses of $\mathcal{O}$(10 9 M ⊙ ), in the first billion years of the Universe remains an open question in astrophysics. At the same time, ultralight dark matter (DM) with mass in the vicinity of $\mathcal{O}$(10 -20 eV) has been motivated by small scale DM distributions. Though this type of DM is constrained by various astrophysical considerations, certain observations could be pointing to modest evidence for it. We present a model with a confining first order phase transition at ~ 10 keV temperatures, facilitating production of $\mathcal{O}$(10 9 M ⊙ ) primordial SMBHs. Such a phase transition can also naturally lead to the implied mass for a motivated ultralight axion DM candidate, suggesting that SMBHs and ultralight DM may be two sides of the same cosmic coin. We consider constraints and avenues to discovery from superradiance and a modification to N eff . On general grounds, we also expect primordial gravitational waves – from the assumed first order phase transition – characterized by frequencies of $\mathcal{O}$(10 -12 - 10 -9 Hz). This frequency regime is largely uncharted, but could be accessible to pulsar timing arrays if the primordial gravitational waves are at the higher end of this frequency range, as could be the case in our assumed confining phase transition.
We present a new class of AI models for the detection of quasi-circular, spinning, non-precessing binary black hole mergers whose waveforms include the higher order gravitational wave modes ($\ell$, |m|) = {(2,2), (2,1), (3,3), (3,2), (4,4)}, and mode mixing effects in the $\ell$ = 3, |m| = 2 harmonics. These AI models combine hybrid dilated convolution neural networks to accurately model both short- and long-range temporal sequential information of gravitational waves; and graph neural networks to capture spatial correlations among gravitational wave observatories to consistently describe and identify the presence of a signal in a three detector network encompassing the Advanced LIGO and Virgo detectors. We first trained these spatiotemporal-graph AI models using synthetic noise, using 1.2 million modeled waveforms to densely sample this signal manifold, within 1.7 h using 256 NVIDIA A100 GPUs in the Polaris supercomputer at the Argonne Leadership Computing Facility. This distributed training approach exhibited optimal classification performance, and strong scaling up to 512 NVIDIA A100 GPUs. With these AI ensembles we processed data from a three detector network, and found that an ensemble of 4 AI models achieves state-of-the-art performance for signal detection, and reports two misclassifications for every decade of searched data. We distributed AI inference over 128 GPUs in the Polaris supercomputer and 128 nodes in the Theta supercomputer, and completed the processing of a decade of gravitational wave data from a three detector network within 3.5 h. Finally, we fine-tuned these AI ensembles to process the entire month of February 2020, which is part of the O3b LIGO/Virgo observation run, and found 6 gravitational waves, concurrently identified in Advanced LIGO and Advanced Virgo data, and zero false positives. This analysis was completed in one hour using one NVIDIA A100 GPU.
We combine the results of an HST STIS and WFPC study of a complete sample of 21 nearby UGC low luminosity radio galaxies with the results of a radio VLA and VLBA study of the same sample. We examine the relationship between the stellar and gaseous properties of the galaxies on tens to hundreds of parsec scale with the properties of the radio jets on the same scale. From the VLA and VLBA data we constrain the physics of the outflowing radio plasma from the tens of parsecs to hundreds of kiloparsec scales. From the WFPC2 H alpha and dust images and the STIS kinematics of the near nuclear gas we obtain constraints on the orientation of near nuclear disks of gas and measures of the nuclear stellar, continuum point source, and line emission fluxes. Under the statistically supported assumption that the radio jet issues perpendicular to the disk, we use the orientation of the optical (large scale accretion?) disks to constrain the three-dimensional orientation of the radio ejection. From HST/STIS spectroscopy of the near-nuclear emission line gas we obtain measures/limits on the black hole masses. We examine correlations between the VLBA and VLA-scale radio emission, the nuclear line emission, and the nuclear optical and radio continuum emission. Though our sample is relatively small, it is uniquely well defined, spans a narrow range in redshift and we have a consistent set of high resolution data with which to carefully examine these relationships. We use the combined radio and optical data to: 1) Constrain the orientation, physics, and bulk outflow speed of the radio plasma; 2) Put limits on the mass accretion rate and study the relationship between black hole mass, radio luminosity, and near nuclear gaseous content; 3) Provide insight into the relationship between BL Lac objects and low luminosity radio galaxies.
String theory has provided a resolution of the puzzles that arise in the quantum theory of black holes. The emerging picture of the hole, encoded in the ‘fuzzball paradigm’, offers deep lessons about the role of quantum gravity on macroscopic length scales. Here, in this article we list these puzzles and explain how they get resolved. We extract the lessons of this resolution in a form that does not involve the technical details of string theory; it is hoped that this form will allow the lessons to be absorbed into other approaches to quantum gravity.
We construct large N saddle points of the matrix model for the $\mathcal{N}$ = 4 Yang- Mills index dual to the BPS black holes in AdS 5 × S 5 , in two different setups. When the two complex chemical potentials for the angular momenta are collinear, we find linear eigenvalue distributions which solve the large N saddle point equation. When the chemical potentials are not collinear, we find novel solutions given by areal eigenvalue distributions after slightly reformulating the saddle point problem. We also construct a class of multi-cut saddle points, showing that they sometimes admit nontrivial filling fractions. As a byproduct, we find that the Bethe ansatz equation emerges from our saddle point equation.
Detections of the tidal disruption flares (TDFs) of stars by supermassive black holes (SMBHs) are rapidly accumulating as optical surveys improve. These detections may provide constraints on SMBH demographics, stellar dynamics, and stellar evolution in galaxies. To maximize this scientific impact, we require a better understanding of how astrophysical parameters interact with survey selection effects in setting the properties of detected flares. In this study, we develop a framework for modeling the distributions of optical TDF detections in surveys across attributes of the host galaxies and the flares themselves. This model folds in effects of the stellar disruption rate in each galaxy, the flare luminosity and temperature distributions, the effects of obscuration and reddening by dust in the host galaxy, and survey selection criteria. We directly apply this model to the sample of TDFs detected by the Zwicky Transient Facility, and find that the overall flare detection rate is in line with simple theoretical expectation. The model can also reproduce the distribution of total stellar mass and redshift of the host galaxies, but fails to match all details of the detected flares, such as their luminosity and temperature distributions. We also find that dust obscuration likely plays an important role in suppressing the TDF detection rate in star-forming galaxies. While we do not find that the unusual preference of TDFs to have hosts in post-starburst galaxies in the "green valley" can be entirely explained by selection effects, our model can help to quantify the true rate enhancement in those galaxies.
Abstract Detection of gravitational waves (GWs) from neutron star-black hole (NSBH) standard sirens provides local measurements of the Hubble constant (H 0 ), regardless of the detection of an electromagnetic (EM) counterpart, given that matter effects can be exploited to break the redshift degeneracy of the GW waveforms. The distinctive merger morphology and the high-redshift detectability of tidally disrupted NSBH make them promising candidates for this method. Also, the detection prospects of an EM counterpart for these systems will be limited toz< 0.8 in the optical, in the era of future GW detectors. Using recent constraints on the equation of state of NSs from multi-messenger observations of NICER and LIGO/Virgo/KAGRA, we show the prospects of measuringH 0 solely from GW observation of NSBH systems, achievable by the Einstein telescope (ET) and Cosmic Explorer (CE) detectors. We first analyze individual events to quantify the effect of high-frequency (≥500 Hz) tidal distortions on the inference of NS tidal deformability parameter (Λ) and hence onH 0 . We find that disruptive mergers can constrain Λ up to ( 60 % ) more precisely than nondisruptive ones. However, this precision is not sufficient to place stringent constraints on theH 0 from individual events. By performing Bayesian analysis on simulated NSBH data (up toN= 100 events, corresponding to a day of observation) in the ET+CE detectors, we find that NSBH systems enable unbiased 4%–13% precision on the estimate ofH 0 (68% credible interval). This is a similar measurement precision found in studies analyzing NSBH mergers with EM counterparts in the LVKC O5 era.
Abstract The spin of a newly formed black hole (BH) at the center of a massive star evolves from its natal value due to two competing processes: accretion of gas angular momentum that increases the spin and extraction of BH angular momentum by outflows that decreases the spin. Ultimately, the final, equilibrium spin is set by a balance between both processes. In order for the BH to launch relativistic jets and power aγ-ray burst (GRB), the BH magnetic field needs to be dynamically important. Thus, we consider the case of a magnetically arrested disk (MAD) driving the spin evolution of the BH. By applying the semianalytic MAD BH spin evolution model of Lowell et al. to collapsars, we show that if the BH accretes ∼20% of its initial mass, its dimensionless spin inevitably reaches small values,a≲ 0.2. For such spins, and for mass accretion rates inferred from collapsar simulations, we show that our semianalytic model reproduces the energetics of typical GRB jets,L jet ∼ 10 50 erg s −1 . We show that our semianalytic model reproduces the nearly constant power of typical GRB jets. If the MAD onset is delayed, this allows powerful jets at the high end of the GRB luminosity distribution,L jet ∼ 10 52 erg s −1 , but the final spin remains low,a≲ 0.3. These results are consistent with the low spins inferred from gravitational wave detections of binary BH mergers. In a companion paper by Gottlieb et al., we use GRB observations to constrain the natal BH spin to bea≃ 0.2.
The exact solution of the relativistic Euler's equation in the black hole geometry is obtained by identifying surfaces of constant angular momentum with the surfaces of constant angular velocity for the azimuthal component. It is shown that the solution gives rise to thick disks and cosmic jets for suitable choices of the physical parameters.
The processes leading to tidal capture of stars by a massive black hole and the consequences of these processes in a dense stellar cluster are discussed in detail. When the amplitude of a tide and the subsequent oscillations are sufficiently large, the energy deposited in a star after periastron passage and formation of a bound orbit cannot be estimated directly using the linear theory of oscillations of a spherical star, but rather numerical estimates must be used. The evolution of a star after tidal capture is discussed. The maximum ratio R of the cross-section for tidal capture to that for tidal disruption is about 3 for real systems. For the case of a stellar system with an empty capture loss cone, even in the case when the impact parameter for tidal capture only slightly exceeds the impact parameter for direct tidal disruption, tidal capture would be much more important than tidal disruption.
Surface brightness maps for thin accretion disks around Schwarzschild and Kerr black holes are presented. These disks are a few times smaller than those used by Rauch and Blandford (1991), and some of the present models are slightly less luminous than theirs. Example of microlensed light curves are calculated by convolving these accretion disk maps with the magnification patterns obtained from microlensing calculations. The light curves exhibit eventlike variations with amplitudes and time scales comparable to those observed in QSO 2237 + 0305. It is concluded that thin thermal accretion disk models are not in contradiction with the observed microlens-induced variations of QSO 2237 + 0305.
Stationary transonic alpha-viscosity models of accretion disks surrounding nonrotating black holes have been investigated. The viscosity is modified such that it vanishes in the supersonic region to ensure its effect does not violate the causality condition. In contrast to previous studies, the viscous stress is taken to be explicitly proportional to the angular velocity gradient and is not assumed to depend solely on the local pressure in the disk. The numerical results reveal that the structure of the innermost regions of the disk are more sensitive to the modified form of the viscosity than to the form of the viscous stress. The critical sonic point is located inside the innermost stable circular orbit of a test particle at 3 Schwarzschild radii. In these solutions, the transition from subsonic to supersonic flow results from pressure effects and not viscous effects. The linear stability of these disks has been examined in the local approximation. It is found that radiative energy transport and viscous stresses in the radial direction can have important effects. As a result, it is shown that the growth rate of the inertial-acoustic mode reaches a maximum at a critical wavelength.
This talk will focus on simulations of binary black hole mergers and the gravitational wave signals they produce. Applications to gravitational wave detection with LISA, and electro~nagnetic counterparts, will be highlighted.
Sufficiently strong and long-lasting first-order phase transitions can produce primordial black holes (PBHs) that contribute substantially to the dark matter abundance of the Universe, and can produce large-scale primordial magnetic fields. Here, we study these mechanisms in a generic class of conformal U(1)' models that also explain active neutrino oscillation data via the type-I seesaw mechanism. We find that phase transitions that occur at seesaw scales between 10 4 GeV and 10 11 GeV produce gravitational wave signals (from the dynamics of the phase transition and from the decay of cosmic string loops) at LISA/ET that can be correlated with microlensing signals of PBHs at the Roman Space Telescope, while scales near 10 11 GeV can be correlated with Hawking evaporation signals at future gamma-ray telescopes. LISA can probe the entire range of PBH masses between 1 × 10 -16 M ⊙ and 8 × 10 -11 M ⊙ if PBHs fully account for the dark matter abundance. For Z' masses between 40 TeV and 10 4 TeV, and 10 TeV right-handed neutrinos, helical magnetic fields can be produced with magnitudes ≳ 0.5 pG and coherence lengths ≳ 0.008 Mpc, above current blazar lower bounds.
We searched for long-duration microlensing events originating from intermediate-mass black holes (BH) in the halo of the Milky Way, using archival data from the EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud (LMC). We combined data from these two surveys to create a common database of light curves for 14.1 million objects in the LMC, covering a total duration of 10.6 years, with flux series measured in four wide passbands. We carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed only by EROS-2 or only by MACHO, over about 7 years, with flux series measured in only two passbands. A likelihood analysis, taking into account the LMC self-lensing and Milky Way disk contributions, allows us to conclude that compact objects with masses in the range 10 – 100 M ⊙ cannot make up more than ~15% of a standard halo total mass (at a 95% confidence level). Our analysis sensitivity weakens for heavier objects, although we still rule out the possibility of ~50% of the halo being made of ~1000 M ⊙ BHs. Combined with previous EROS results, an upper limit of ~15% of the total halo mass can be obtained for the contribution of compact halo objects in the mass range 10 –6 – 10 2 M ⊙ .
We propose a new scenario for the formation of asteroid-mass primordial black holes (PBHs). Our mechanism is based on the annihilation of the string-wall network associated with the breaking of a U(1) global symmetry into a discrete Z N symmetry. If the potential has multiple local minima ( N > 1) the network is stable, and the annihilation is guaranteed by a bias among the different vacua. The collapse of the string-wall network is accompanied by catastrogenesis , a large production of pseudo-Goldstone bosons (pGBs) — e.g. axions, ALPs, or majorons — gravitational waves, and PBHs. If pGBs rapidly decay into products that thermalize, as predicted e.g. in the high-quality QCD axion and heavy majoron models, they do not contribute to the dark matter population, but we show that PBHs can constitute 100% of the dark matter. The gravitational wave background produced by catastrogenesis with heavy unstable axions, ALPs, or majorons could be visible in future interferometers.
We present global 3D radiation magnetohydrodynamic simulations of accretion onto a 6.62 solar-mass black hole, with quasi-steady-state accretion rates reaching 0.016–0.9 times the critical accretion rate, which is defined as the accretion rate for powering the Eddington luminosity, assuming a 10% radiative efficiency, in three different runs. The simulations show no sign of thermal instability over hundreds of thermal timescales at 10 r g . The energy dissipation occurs close to the mid-plane in the near-critical runs and near the disk surface in the low–accretion rate run. The total radiative luminosity inside ~20 r g is about 1%–30% of the Eddington limit, with radiative efficiencies of about 6% and 3%, respectively, in the sub- and near-critical accretion regimes. In both cases, self-consistent turbulence generated by the magnetorotational instability leads to angular momentum transfer, and the disk is supported by magnetic pressure. Outflows from the central low-density funnel, with a terminal velocity of ~0.1c, are seen only in the near-critical runs. We conclude that these magnetic pressure–dominated disks are thermally stable and thicker than the α disk, and that the effective temperature profiles are much flatter than those in the α disks. The magnetic pressures of these disks are comparable within an order of magnitude to the previous analytical magnetic pressure–dominated disk model.