Black Hole Research Articles

Charged spherically symmetric and slowly rotating charged black hole solutions in bumblebee gravity

Abstract In this paper, we study the scenario in which the matter field is an electromagnetic field nonminimally coupled to the bumblebee vector field. We present exact charged spherically symmetric black hole solutions and slowly rotating charged solutions in bumblebee gravity with and without a cosmological constant. The static spherically symmetric solutions describe the Reissner–Nordström-like black hole and Reissner–Nordström-(anti) de Sitter-like black hole, while the stationary and axially symmetric solutions describe the Kerr–Newman-like black hole and Kerr–Newman–(anti) de Sitter-like black hole. We utilize the Hamilton–Jacobi formalism to study the shadows of the black holes. Additionally, we investigate the effect of the electric charge and Lorentz-violating parameters on the radius of the shadow reference circle and the distortion parameter. We find that the radius of the reference circle decreases with the Lorentz-violating parameter and the charge parameter, while the distortion parameter increases with the Lorentz-violating parameter and the charge parameter.

Neutrino-dominated Relativistic Viscous Accretion Flows around Rotating Black Holes with Shocks

Abstract We investigate the relativistic, viscous, advective neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes, incorporating neutrino cooling. By adopting an effective potential to describe the spacetime geometry around the rotating black holes, we self-consistently solve the governing NDAF equations to obtain global transonic accretion solutions. Our findings indicate that, depending on the model parameters, namely, energy (ε), angular momentum (λ), accretion rate ( m ̇ ), viscosity (α), and black hole spin (a k), NDAFs may harbor standing shocks where the Rankine–Hugoniot shock conditions are satisfied. Utilizing these shock-induced NDAF solutions, we compute the neutrino luminosity (L ν ) and neutrino annihilation luminosity ( L ν ν ¯ ) across a wide range of model parameters. We further calculate maximum neutrino luminosity ( L ν max ) and neutrino annihilation luminosity ( L ν ν ¯ max ), resulting in L ν max ∼ 1 0 51 − 53 erg s−1 (1048−51 erg s−1) and L ν ν ¯ max ∼ 1 0 48 − 52 erg s−1 (1042−49 erg s−1) for a k = 0.99 (0.0). These findings suggest that shocked NDAF solutions are potentially promising to explain the energy output of gamma-ray bursts (GRBs). We employ our NDAF model formalism to elucidate L ν ν ¯ obs for five GRBs with known redshifts and estimate their accretion rate ( m ̇ ) based on the spin (a k) of the central source of the GRBs studied here.

The Information Loss Problem and Hawking Radiation as Tunneling

In this paper, we review some methods that have tried to solve the information loss problem. In particular, we revisit the solution based on Hawking radiation as tunneling and provide a detailed statistical interpretation of the black hole entropy in terms of the quantum tunneling probability of Hawking radiation from the black hole. In addition, we show that black hole evaporation is governed by a time-dependent Schrödinger equation that sends pure states into pure states rather than into mixed states (Hawking had originally established that the final result would be mixed states). This is further confirmation of the fact that black hole evaporation is unitary.

Radio emission from little red dots may reveal their true nature

The unprecedented sensitivity of the James Webb Space Telescope (JWST) has revolutionized our understanding of the early Universe. Among the most intriguing JWST discoveries are red, very compact objects that show broad line emission features, nicknamed little red dots (LRDs). The discovery of LRDs has triggered great interest in their origin as either extremely starbursting galaxies or highly obscured active galactic nuclei (AGNs). Their exact nature remains unknown. The goal of this work is to estimate the radio emission from LRDs and predict which radio surveys would detect them. To achieve these objectives, we employed the fundamental plane of black hole (BH) accretion to estimate radio emission from AGNs and the stellar radio fluxes from their host galaxies. We assumed a range of BH masses, X-ray luminosities (rm L_ X ), and star formation rates (SFRs) to bracket the likely properties of LRDs. Our findings suggest that BH radio fluxes from LRDs are 10-100 times higher than the stellar fluxes from their host galaxies, depending on the BH mass, rm L_X, and SFR. The detection of a ∼ 500 nJy signal above 2 GHz at z ≥ 5 or a ∼ 2000 nJy flux at z = 3-4 would be a smoking gun for the presence of AGNs provided that SFRs in the host galaxies are rm < 30 We find that LRDs are most likely radio-quiet AGNs; otherwise, they would have already been detected in the current radio surveys. Our findings suggest that LRDs can be detected with upcoming radio observatories such as ngVLA and SKA with integration times of 10-100 hrs, respectively.

Assessing the Dark Matter Content of Two Quasar Host Galaxies at z ∼ 6 through Gas Kinematics

Abstract We conduct a study of the gas kinematics of two quasar host galaxies at z ≳ 6 traced by the [C ii] emission line using the Atacama Large Millimeter/submillimeter Array. By combining deep observations at both low and high resolution, we recover the diffuse emission, resolve its structure, and measure the rotation curves from the inner region of the galaxy to its outskirts using DysmalPy and 3D Barolo. Assuming that both galaxies exhibit disk rotation driven by the gravitational potential of the galaxy, we find that the best-fit disk models have a V rot/σ ≈ 2 and inferred circular velocities out to ∼6–8 kpc scales, well beyond the likely stellar distribution. We then determine the mass profiles of each component (stars, gas, dark matter) with priors on the baryon and dark matter properties. We find relatively large dark matter fractions within their effective radii (f DM(R < R e) = 0.61 − 0.08 + 0.08 and 0.53 − 0.23 + 0.20 , respectively), which are significantly larger than those extrapolated from lower redshift studies and remain robust under different input parameters verified by Monte Carlo simulations. The large f DM(R < R e) corresponds to halo masses of ∼1012.5−1012.8 M ⊙, thus representative of the most massive halos at these redshifts. Notably, while the masses of these supermassive black holes (SMBHs) are approximately 1 dex higher than the low-redshift relationship with stellar mass, the closer alignment of SMBH and halo masses with a local relationship may indicate that the early formation of these SMBHs is linked to their dark matter halos, providing insights into the coevolution of galaxies and black holes in the early Universe.

The impact of compact object deformation on thin accretion disk properties

Abstract We investigate the standard relativistic geometrically thin and optically thick accretion disk in the background of a deformed compact object. The main purpose of this work is to determine whether such a deformed object possesses its own observational fingerprint that can distinguish it from Schwarzschild and Kerr black holes. Our analysis reveals the properties of this relativistic accretion disk model and its dependence on the initial parameters.

Millihertz oscillations near the innermost orbit of a supermassive black hole

Millihertz oscillations near the innermost orbit of a supermassive black hole

Striking a Chord with Spectral Sirens: Multiple Features in the Compact Binary Population Correlate with H0

Abstract Spectral siren measurements of the Hubble constant (H 0) rely on correlations between observed detector-frame masses and luminosity distances. Features in the source-frame mass distribution can induce these correlations. It is crucial, then, to understand (i) which features in the source-frame mass distribution are robust against model (re)parameterization, (ii) which features carry the most information about H 0, and (iii) whether distinct features independently correlate with cosmological parameters. We study these questions using real gravitational-wave observations from the LIGO-Virgo-KAGRA Collaborations' third observing run. Although constraints on H 0 are weak, we find that current data reveals several prominent features in the mass distribution, including peaks in the binary black hole source-frame mass distribution near ∼9M ⊙ and ∼32M ⊙ and a roll-off at masses above ∼46M⊙. For the first time using real data, we show that all of these features carry cosmological information and that the peak near ∼32M ⊙ consistently correlates with H 0 most strongly. Introducing model-independent summary statistics, we show that these statistics independently correlate with H 0, exactly what is required to limit systematics within future spectral siren measurements from the (expected) astrophysical evolution of the mass distribution.

Addressing the "Black Hole" of Low Back Pain Care With Clinical Decision Support: User-Centered Design and Initial Usability Study.

Low back pain (LBP) is a highly prevalent problem causing substantial personal and societal burden. Although there are specific types of LBP, each with evidence-based treatment recommendations, most patients receive a nonspecific diagnosis that does not facilitate evidence-based and individualized care. We designed, developed, and initially tested the usability of a LBP diagnosis and treatment decision support tool based on the available evidence for use by clinicians who treat LBP, with an initial focus on chiropractic care. Our 3-step user-centered design approach consisted of identifying clinical requirements through the analysis of evidence reviews, iteratively identifying task-based user requirements and developing a working web-based prototype, and evaluating usability through scenario-based interviews and the System Usability Scale. The 5 participating users had an average of 18.5 years of practicing chiropractic medicine. Clinical requirements included 44 patient interview and examination items. Of these, 13 interview items were enabled for all patients and 13 were enabled conditional on other input items. One examination item was enabled for all patients and 16 were enabled conditional on other items. One item was a synthesis of interview and examination items. These items provided evidence of 12 possible working diagnoses of which 3 were macrodiagnoses and 9 were microdiagnoses. Each diagnosis had relevant treatment recommendations and corresponding patient educational materials. User requirements focused on tasks related to inputting data, and reviewing and selecting working diagnoses, treatments, and patient education. User input led to key refinements in the design, such as organizing the input questions by microdiagnosis, adding a patient summary screen that persists during data input and when reviewing output, adding more information buttons and graphics to input questions, and providing traceability by highlighting the input items used by the clinical logic to suggest a working diagnosis. Users believed that it would be important to have the tool accessible from within an electronic health record for adoption within their workflows. The System Usability Scale score for the prototype was 84.75 (range: 67.5-95), considered as the top 10th percentile. Users believed that the tool was easy to use although it would require training and practice on the clinical content to use it effectively. With such training and practice, users believed that it would improve care and shed light on the "black hole" of LBP diagnosis and treatment. Our systematic process of defining clinical requirements and eliciting user requirements to inform a clinician-facing decision support tool produced a prototype application that was viewed positively and with enthusiasm by clinical users. With further planned development, this tool has the potential to guide clinical evaluation, inform more specific diagnosis, and encourage patient education and individualized treatment planning for patients with LBP through the application of evidence at the point of care.

Survey of radiative, two-temperature magnetically arrested simulations of the black hole M87* I: Turbulent electron heating

Abstract We present a set of eleven two-temperature, radiative, general relativistic magnetohydrodynamic (2TGRRMHD) simulations of the black hole M87* in the magnetically arrested (MAD) state, surveying different values of the black hole spin a*. Our 3D simulations self-consistently evolve the temperatures of separate electron and ion populations under the effects of adiabatic compression/expansion, viscous heating, Coulomb coupling, and synchrotron, bremsstrahlung, and inverse Compton radiation. We adopt a sub-grid heating prescription from gyrokinetic simulations of plasma turbulence. Our simulations have accretion rates $\dot{M}=(0.5-1.5)\times 10^{-6}\dot{M}_{\rm Edd}$ and radiative efficiencies εrad = 3 − 35 %. We compare our simulations to a fiducial set of otherwise identical single-fluid GRMHD simulations and find no significant changes in the outflow efficiency or black hole spindown parameter. Our simulations produce an effective adiabatic index for the two-temperature plasma of Γgas ≈ 1.55, larger than the Γgas = 13/9 value often adopted in single-fluid GRMHD simulations. We find moderate ion-to-electron temperature ratios in the 230 GHz emitting region of R = Ti/Te ≈ 5. While total intensity 230 GHz images from our simulations are consistent with Event Horizon Telescope (EHT) results, our images have significantly more beam-scale linear polarization (〈|m|〉 ≈ 30 %) than is observed in EHT images of M87* (〈|m|〉 < 10 %). We find a trend of the average linear polarization pitch angle ∠β2 with black hole spin consistent with what is seen in single-fluid GRMHD simulations, and we provide a simple fitting function for ∠β2(a*) motivated by the wind-up of magnetic field lines by black hole spin in the Blandford-Znajek mechanism.

Primary scalar hair in Gauss–Bonnet black holes with Thurston horizons

Abstract In this work, we construct novel asymptotically locally AdS $$_5$$ 5 black hole solutions of Einstein–Gauss–Bonnet theory at the Chern–Simons point, supported by a scalar field that generates a primary hair. The strength of the scalar field is governed by an independent integration constant; when this constant vanishes, the spacetime reduces to a black hole geometry devoid of hair. The existence of these solutions is intrinsically tied to the horizon metric, which is modeled by three non-trivial Thurston geometries: Nil, Solv, and $$SL(2,{\mathbb {R}}).$$ S L ( 2 , R ) . The quadratic part of the scalar field action corresponds to a conformally coupled scalar in five dimensions -an invariance of the matter sector that is explicitly broken by the introduction of a quartic self-interaction. These black holes are characterized by two distinct parameters: the horizon radius and the temperature. Notably, there exists a straight line in this parameter space along which the horizon geometry exhibits enhanced isometries, corresponding to solutions previously reported in JHEP 02, 014 (2014). Away from this line, for a fixed horizon radius and temperatures above or below a critical value, the metric’s isometries undergo spontaneous breaking. Employing the Regge–Teitelboim approach, we compute the mass and entropy of these solutions, both of which vanish. Despite this, only one of the integration constants can be interpreted as hair, as the other modifies the local geometry at the conformal boundary. Finally, for Solv horizon geometries, we extend these hairy solutions to six dimensions.

Black Hole Supernovae, Their Equation of State Dependence, and Ejecta Composition

Abstract Recent literature on core-collapse supernovae suggests that a black hole (BH) can form within ∼1 s of shock revival, while still culminating in a successful supernova. We refer to these as BH supernovae, as they are distinct from other BH formation channels in both timescale and impact on the explosion. We simulate these events self-consistently from core collapse until 20–50 days after collapse using three axisymmetric models of a 60 M ⊙ zero-age main-sequence progenitor star and investigate how the composition of the ejecta is impacted by the BH formation. We employ Skyrme-type equations of state (EOSs) and vary the uncertain nucleonic effective mass, which affects the pressure inside the proto–neutron star through the thermal part of the EOS. This results in different BH formation times and explosion energies at BH formation, yielding final explosion energies between 0.06 and 0.72 × 1051 erg with 21.8–23.3 M ⊙ of ejecta, of which 0–0.018 M ⊙ is 56Ni. Compared to expectations from 1D simulations, we find more nuanced EOS dependences of the explosion dynamics, the mass of the BH remnant, and the elemental composition of the ejecta. We investigate why the explosions survive despite the massive overburden and link the shape of the diagnostic energy curve and character of the ejecta evolution to the progenitor structure.

It's written in the massive stars: The role of stellar physics in the formation of black holes

In the age of gravitational-wave (GW) sources and newly discovered local black holes (BHs) and neutron stars (NSs), understanding the fate of stars is a key question. Not every massive star is expected to successfully explode as a supernova (SN) and leave behind a NS; some stars form BHs. The remnant left after core collapse depends on explosion physics but also on the final core structure, often summarized by the compactness parameter or iron core mass, where high values have been linked to BH formation. Several independent groups have reported similar patterns in these parameters as a function of mass, characterized by a prominent ``compactness peak'' followed by another peak at higher masses, pointing to a common underlying physical mechanism. Here, we investigate the origin of this pattern by computing detailed single-star models of 17 to 50 solar masses with MESA. We show that the timing and energetics of the last nuclear burning phases determine whether or not stars will reach a high final compactness and iron-core mass and will likely form BHs. The first and second compactness increases originate from core carbon and neon burning, respectively, becoming neutrino dominated, which enhances the core contraction and ultimately increases the iron-core mass and compactness. An early core neon ignition during carbon burning, and an early silicon ignition during oxygen burning, both help counter the core contraction and decrease the final iron core mass and compactness. Shell mergers between C/Ne-burning and O-burning shells further decrease the compactness and we show that these mergers are due to an enhanced entropy production in those layers. We find that the final structure of massive stars is not random but already ``written'' in their cores at core helium exhaustion, when the core structure is characterized by the central carbon mass fraction $X_ C $ and the CO core mass. The same mechanisms determine the final structure of any star in this core mass range, including binary products; though binary interactions induce a systematical shift in the range of expected BH formation due to changes in $X_ C $. Finally, we discuss the role of uncertainties in stellar physics and how to apply the findings presented here to studies of GW sources.

Microscopic entropy of static black holes in 3D Lovelock gravities

We give a microscopic derivation of the semiclassical entropy of static black holes in 3D Lovelock gravities, which are certain 3D Horndeski theories that were recently discovered from higher-dimensional Lovelock gravities via various methods and admit black hole solutions analogous to higher-dimensional ones. Assuming the ground state is described by the soliton obtained from the black hole solution by performing a double Wick rotation, we reproduce the semiclassical entropy from the Cardy formula without central charges for the asymptotic growth of the number of states. We explain in detail how the mass of the soliton, which is needed in the Cardy formula, can be computed in the minisuperspace formalism. Published by the American Physical Society 2025

Weak gravity conjecture validation with photon spheres of quantum corrected Reissner–Nordstrom–AdS black holes in Kiselev spacetime

Abstract In this study, we investigate the Weak Gravity Conjecture (WGC) in the context of quantum-corrected Reissner–Nordstrom–AdS (RN-AdS) black holes within Kiselev spacetime. Our focus is on photon spheres, which serve as markers for stable and unstable photon spheres. We confirm the validity of the WGC by demonstrating that quantum corrections do not alter the essential charge-to-mass ratio, thereby supporting the conjecture’s universality. Our analysis reveals that black holes with a charge greater than their mass $$(Q > M)$$ ( Q > M ) possess photon spheres or exhibit a total topological charge of the photon sphere $$(\text {PS} = -1),$$ ( PS = - 1 ) , which upholds the WGC. This finding is significant as it reinforces the conjecture’s applicability even in the presence of quantum corrections. Furthermore, we examine various parameter configurations to understand their impact on the WGC. Specifically, we find that configurations with $$\omega = -\frac{1}{3}$$ ω = - 1 3 and $$\omega = -1$$ ω = - 1 maintain the conjecture, indicating that these values do not disrupt the charge-to-mass ratio required by the WGC. However, for $$\omega = -\frac{4}{3},$$ ω = - 4 3 , the conjecture does not hold, suggesting that this particular parameter value leads to deviations from the expected behavior. These results open new directions for research in quantum gravity, as they highlight the importance of specific parameter values in maintaining the WGC. The findings suggest that while the WGC is robust under certain conditions, there are scenarios where it may be challenged, prompting further investigation into the underlying principles of quantum gravity.

Symmetry restoration and vacuum decay from accretion around black holes

Vacuum decay and symmetry breaking play an important role in the fundamental structure of the matter and the evolution of the Universe. In this work we study how the purely classical effect of accretion of fundamental fields onto black holes can lead to shells of symmetry restoration in the midst of a symmetry broken phase. We also show how it can catalyze vacuum decay, forming a bubble that expands asymptotically at the speed of light. These effects offer an alternative, purely classical mechanism to quantum tunneling for seeding phase transitions in the Universe. Published by the American Physical Society 2025

X-ray polarization from accretion disk winds

X-ray polarimetry is a fine tool for probing the accretion geometry and physical processes operating in the proximity of compact objects, such as black holes and neutron stars. Recent discoveries made by the Imaging X-ray Polarimetry Explorer question our understanding of the accretion picture. The observed high levels of X-ray polarization in X-ray binaries and active galactic nuclei are challenging to achieve within the conventional scenarios. We investigate the possibility that a fraction (or even all) of the observed polarized signal arises from scattering in the equatorial accretion disk winds, the slow and extended outflows, which are often detected in these systems via spectroscopic means. We find that wind scattering can reproduce the levels of polarization that are observed in these sources.

A 22 Billion M⊙ Black Hole in Holmberg 15A with Keck KCWI Spectroscopy and Triaxial Orbit Modeling

Abstract Holmberg 15A (H15A), the brightest cluster galaxy of A85, has an exceptionally low central surface brightness even among local massive elliptical galaxies with distinct stellar cores, making it exceedingly challenging to obtain high-quality spectroscopy to detect a supermassive black hole (SMBH) at its center. Aided by the superb sensitivity and efficiency of KCWI at the Keck II Telescope, we have obtained spatially resolved stellar kinematics over a ∼100″ × 100″ contiguous field of H15A for this purpose. The velocity field exhibits a low-amplitude (∼20 km s−1) rotation along a kinematic axis that is prominently misaligned from the photometric major axis, a strong indicator that H15A is triaxially shaped with unequal lengths for the three principal axes. Using 2500 observed kinematic constraints, we perform extensive calculations of stellar orbits with the triaxial Schwarzschild code, TriOS, and search over ∼40,000 galaxy models to simultaneously determine the mass and intrinsic 3D shape parameters of H15A. We determine a ratio of p = 0.89 for the middle-to-long principal axes and q = 0.65 for the short-to-long principal axes. Our best estimate of the SMBH mass, M BH = ( 2.1 6 − 0.18 + 0.23 ) × 1 0 10 M ⊙ , makes H15A—along with NGC 4889—the galaxy hosting the most massive SMBHs known in the local Universe. Both SMBHs lie significantly above the mean M BH–σ scaling relation. Repeating the orbit modeling with the axisymmetrized version of TriOS produces worse fits to the KCWI kinematics and increases M BH to (2.55 ± 0.20) × 1010 M ⊙, which is still significantly below the M BH = (4.0 ± 0.8) × 1010 M ⊙ reported in a prior axisymmetric study of H15A.

Relativistic Binary Precession: Impact on Eccentric Massive Binary Black Hole Accretion and Hydrodynamics

Abstract Recent hydrodynamical simulations have shown that circumbinary gas disks drive the orbits of massive binary black holes (BHs) to become eccentric, even when general relativistic (GR) corrections to the orbit are significant. Here, we study the GR apsidal precession of eccentric equal-mass massive binary BHs in circumbinary disks via two-dimensional hydrodynamical simulations. We perform a suite of simulations comparing precessing and nonprecessing binaries across a range of eccentricities, semimajor axes, and precession rates. We find that the GR precession of the binary's semimajor axis can introduce a dominant modulation in the binary's accretion rate and the corresponding high-energy electromagnetic light curves. We discuss the conditions under which this occurs and its detailed characteristics and mechanism. Finally, we discuss the potential to observe these precession signatures in electromagnetic- and gravitational-wave observations, as well as the precession signal's unique importance as a potential tool to constrain the mass, eccentricity, and semimajor axis of binary merger events.

The evolution of extragalactic peaked-spectrum sources down to 54 megahertz

Peaked-spectrum sources, known for their distinct peaked radio spectra, are a type of radio-loud active galactic nuclei. One subtype, megahertz-peaked-spectrum (MPS) sources, which exhibit a spectral peak at a frequency of a hundred megahertz, have emerged as a potential tool for identifying high-redshift candidates. However, the potential evolutionary link between the fraction of these sources and their redshifts remains unclear and requires further investigation. The recent, high-sensitivity Low Frequency Array (LOFAR) surveys enable statistical studies of these objects down to ultra-low frequencies (< 150 MHz). In this study we first used the multi-radio data to investigate the evolution of spectral index with redshift for 1,187 quasars from the 16th SDSS quasar catalog. For each quasar, we analyzed available data from the LOFAR Low Band Antenna at 54 MHz, the High Band Antenna at 144 MHz, and the Very Large Array Faint Images of the Radio Sky at Twenty centimeters at 1.4 GHz. We measured the spectral index (α^ and α^ ) and find no significant change in their median values with redshift. Extended sources have steeper spectral indices than compact sources, which is consistent with previous findings. Based on the spectral index information, we identified MPS sources using the criteria rm α^ >= 0.1 and rm α^ < 0, and analyzed their properties. We find that the fraction of MPS sources is constant with the redshift ($0.1-4.8$), bolometric luminosity (rm 10^ erg/s), and supermassive black hole mass (rm 10^ M_ ⊙ ), which suggests that MPS sources have relatively stable physical conditions or formation mechanisms across various evolutionary stages and environments.