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Zeldovich amplification of classic waves carrying orbital angular momentum (OAM) from a rotating absorber is an extension of Penrose superradiance from a rotating black hole. The demonstration of Zeldovich amplification in recently published experiments showed the possibility of extracting energy from a spinning black hole or a rotating absorber. However, it remains unclear whether extracting energy from non-absorbent bodies is possible. Here, we experimentally demonstrate the amplification of acoustic OAM from rotating impellers made of non-absorbent materials. We develop a multichannel least-mean-square algorithm to emit high-charge acoustic OAM beams into three types of impellers. The acoustic gains (more than 20 dB) have been measured by both a static microphone and a microphone array working as a virtual rotating receiver. The results indicate that the acoustic gain from the impeller with a large windward area is much higher than the ones with a small area. Our work is worthwhile in proposing the experimental method to study the phenomenon of acoustic OAM amplification and showing prospects in industrial applications such as amplifying acoustic signals by commonly used impellers. Our work also discusses a possible way of extracting energy from non-absorbent celestial systems, such as the orbiting planets of the Solar system, which are much less absorbent to light but much closer to the Earth than a black hole. [ABSTRACT FROM AUTHOR]

A new class of acoustic black hole (ABH) waveguides is presented, which relies in its operation on an array of optimally designed functionally graded perforated rings (FGPRs). In this manner, the developed ABH is provided with built-in energy dissipation characteristics generated by virtue of the flow through perforations, which enhances its acoustic absorption behavior and makes the speed of the propagating waves vanish faster when reaching the end of the waveguide. Furthermore, the particular design of the rings enables sandwiching of additional porous absorbing layers between the rings to further boost the absorption characteristics of the proposed ABH. Accordingly, the operating principle of the new class of ABH is radically different from that of the conventional ABH that employs sequential solid-flat rings of decreasing inner radii to create a virtual power law taper necessary for generating the black hole effect, but through reactive means rather than the effective dissipative means of the proposed ABH. Therefore, this paper develops a transfer matrix modeling (TMM) approach to model the absorption and reflection characteristics of the new class of ABH, in an attempt to predict its behavior, optimize the selection of its design parameters, and more importantly, demonstrate its merits as effective means for controlling sound propagation. Numerical examples are presented to highlight the merits and behavior of the proposed ABH. Predictions of the TMM are validated against experimental results that are available in the literature for one and two micro-perforated plates. Comparisons are also established between the ABH with FGPR and the conventional ABH in order to distinguish the behavior and underlying principles of their operations. [ABSTRACT FROM AUTHOR]

JWST is revealing a remarkable new population of high-redshift (z ≳ 4), low-luminosity active galactic nuclei in deep surveys and detecting the host galaxy's stellar light in the most luminous and massive quasars at z ∼ 6 for the first time. Recent findings claim that supermassive black holes (SMBHs) in these systems are significantly more massive than predicted by the local black hole (BH) mass–stellar mass ( M BH - M ⋆ ) relation and that this is not due to sample selection effects. Through detailed statistical modeling, we demonstrate that the coupled effects of selection biases (i.e., finite detection limit and requirements for detecting broad lines) and measurement uncertainties can largely explain the reported offset and flattening in the observed M BH - M ⋆ relation toward the upper envelope of the local relation, even for those at M BH < 1 0 8 M ⊙ . We further investigate the possible evolution of the M BH - M ⋆ relation at z ≳ 4 with careful treatment of observational biases and consideration of the degeneracy between intrinsic evolution and dispersion in this relation. The bias-corrected intrinsic M BH - M ⋆ relation in the low-mass regime ( M ⋆ ≲ 1 0 10 M ⊙ ) suggests a large population of low-mass BHs ( M BH ≲ 1 0 5 M ⊙ ), possibly originating from lighter seeds, may remain undetected or unidentified. These results underscore the importance of forward modeling observational biases to better understand BH seeding and SMBH–galaxy coevolution mechanisms in the early universe, even with the deepest JWST surveys. [ABSTRACT FROM AUTHOR]

The quasiperiodic oscillations (QPOs) observed in the X-ray variability of both black hole (BH) and neutron star (NS) systems provide a tool for probing strong gravity and dense matter equations of state. Nevertheless, the mechanism of QPO modulation in NS systems, where the amplitudes of QPOs with frequencies approaching the kHz range are very high in comparison to BH high-frequency QPOs, remains an unsolved puzzle. Relativistic ray tracing of photons emitted from the immediate vicinity of compact objects has, to date, been used to investigate various mechanisms that explain the observed weak BH QPOs. However, it has not been applied to model the NS QPO signal, which requires incorporating the NS surface and a bright boundary layer (BL) on it. Here, we explore the QPO modulation mechanisms based on the BL obscuration. Using simplified models of axisymmetric oscillations of thick accretion disks (tori), we demonstrate that the disk oscillations drive the high NS QPO amplitudes through BL obscuration, which is relevant, especially for vertical oscillations. We also demonstrate that obscuration effects enable the observability of the Keplerian frequency in the case of disks that decay due to instabilities. [ABSTRACT FROM AUTHOR]

In the summer of 2023, the pulsar timing arrays (PTAs) announced a compelling evidence for the existence of a nanohertz stochastic gravitational wave background (SGWB). Despite this breakthrough, however, several critical questions remain unanswered: What is the source of the signal? How can cosmic variance be accounted for? To what extent can we constrain nanohertz gravity? When will individual supermassive black hole binaries become observable? And how can we achieve a stronger detection? These open questions have spurred significant interests in PTA science, making this an opportune moment to revisit the astronomical and theoretical foundations of the field, as well as the data analysis techniques employed. In this review, we focus on the theoretical aspects of the SGWB as detected by PTAs. We provide a comprehensive derivation of the expected signal and its correlation, presented in a pedagogical manner, while also addressing current constraints. Looking ahead, we explore future milestones in the field, with detailed discussions on emerging theoretical considerations such as cosmic variance, the cumulants of the one- and two-point functions, subluminal gravitational waves, and the anisotropy and polarization of the SGWB. [ABSTRACT FROM AUTHOR]

We find new classes of the dynamical black hole solutions in five- or higher-dimensional Einstein–Maxwell-dilaton theory, in which the dilaton field interacts nontrivially with the Maxwell field, and the cosmological constant, with two arbitrary coupling constants. The solutions which are nonstationary, and almost conformally regular everywhere, are constructed by embedding the four-dimensional self-dual geometries. We consider three different situations, where the two coupling constants are not equal, are nonzero equal and finally both are zero. We also consider the cases where one of the metric functions, depends on one coordinate only, and another interesting case where it depends on two spatial coordinates. We also find that the cosmological constant can take all possible negative, zero and positive values, hence our solutions are asymptotically anti-de Sitter, flat and de Sitter. We discuss the properties of the solutions which are the analytic description of coalescing black holes in any dimensions, greater or equal to five. [ABSTRACT FROM AUTHOR]

The formation of compact binary systems is largely driven by their evolution through a common envelope (CE) phase, crucial for understanding phenomena such as type Ia supernovae and black hole mergers. Despite their importance, direct observational evidence for CE material has been elusive due to the transient nature of these envelopes. Numerical simulations suggest that some envelope material may persist post-ejection. In this study, we investigate circumstellar material (CSM) surrounding hot subdwarf (sdB) stars, focusing on material ejected during the CE phase of binary evolution. We analyse Ca  ii K absorption lines in 727 sdB candidates from the LAMOST-LRS survey, selecting 145 stars with strong absorption features, indicating the presence of CSM. We compare the velocities of the Ca  ii K lines with the systemic velocities of sdB binaries, confirming that the material originates from ejected CE material. The results show that the CSM persists long after the CE event, suggesting the formation of a stable, long-lived circumstellar environment around sdB stars. This study enhances our understanding of the role of CSM in post-CE evolution and provides new insights into the physical processes shaping the evolution of sdB binaries. [ABSTRACT FROM AUTHOR]

We examine the nature, origin, and fate of early (⁠|$z\ge 2$|⁠) massive (⁠|$M_\star \gt 10^{10}\,\mathrm{ M}_\odot$|⁠) quenched galaxies (EQGs) in a new |$(100\,h^{-1}\,{\rm Mpc}^3)$| run of the simba-C galaxy formation model. We define 'quenched' to be |$\gt 4\sigma$| below an iterative polynomial fit to the star-forming sequence (SFS), and find that simba-C produces EQGs as early as |$z\sim 5$| and number densities agreeing with observations at |$z\lesssim 3$| (though slightly low at |$z\gtrsim 4$|⁠). Using a photometric-based EQG selection or a fixed specific star formation rate cut of |$10^{-10}$|  yr |$^{-1}$| yields similar results. EQGs predominantly arise in central galaxies with stellar mass |$M_\star \sim 10^{10.5-11.3}\,\rm{M}_\odot$|⁠ , not necessarily the most massive systems. A Uniform Manifold Approximation and Projection shows that quenched galaxies have notably large black hole-to-stellar mass ratios, lower rotational support, and less dust, but are not atypical versus similar-mass non-EQGs in their environments, halo mass, or halo gas temperatures at the time of quenching. However, via galaxy tracking we show that the progenitor environments of EQGs are significantly more overdense than that of non-EQGs, which drives higher black hole mass fractions and stellar-to-halo mass ratios. This results in the Eddington ratio dropping sufficiently low for simba-C 's jet mode feedback to turn on, which quickly quenches the host galaxies. EQGs thus seem to be galaxies that grow their black holes quickly within highly dense environments, but end up in moderately dense environments where black hole feedback can quench effectively. We find that |$\gtrsim 30~{{\ \rm per\ cent}}$| of EQGs rejuvenate, but the rejuvenating fraction drops quickly below |$z\lesssim 2$|⁠. By |$z=0$|⁠ , it is difficult to distinguish the descendants of EQGs versus non-EQGs. [ABSTRACT FROM AUTHOR]

As gravitational wave detections increase the number of observed compact binaries (consisting of neutron stars or blacks), we begin to probe the different conditions producing these binaries. Most studies of compact remnant formation focus either on stellar collapse from the evolution of field binary stars in gas-free environments or on the formation of stars in clusters where dynamical interactions capture the compact objects, forming binaries. But a third scenario exists. In this paper, we study the fate of massive stars formed, accrete gas, and evolve in the dense discs surrounding supermassive black holes. We calculate the explosions produced and compact objects formed by the collapse of these massive stars. Nucleosynthetic yields may provide an ideal, directly observable, diagnostic of the formation and fate of these stars in active galactic nuclei. We present a first study of the explosive yields from these stars, comparing these yields with the observed nucleosynthetic signatures in the discs around supermassive stars with quasars. We show that, even though these stars tend to form black holes, their rapid rotation leads to discs that can eject a considerable amount of iron during the collapse of the star. The nucleosynthetic yields from these stars can produce constraints on the number of systems formed in this manner, but further work is needed to exploit variations from the initial models presented in this paper. [ABSTRACT FROM AUTHOR]

This study explores the formation and implications of mini-active galactic nucleus (mAGN) discs around intermediate-mass black holes (IMBHs) embedded in gas-rich globular/nuclear clusters (GCs). We examine the parameter space for stable mAGN discs, considering the influence of IMBH mass, disc radius, and gas density on disc stability. The dynamics of stars and black holes within the mAGN disc are modelled, with a focus on gas-induced migration and gas dynamical friction. These dynamical processes can lead to several potentially observable phenomena, including the enhancement of gravitational wave mergers (particularly intermediate-mass ratio inspirals and extreme-mass ratio inspirals), and the occurrence of milli/centi-tidal disruption events with unique observational signatures. We find that gas hardening can significantly accelerate the inspiral of binaries within the disc, potentially leading to a frequency shift in the emitted gravitational waves. Additionally, we explore the possibility of forming accreting IMBH systems from captured binaries within the mAGN disc, potentially resulting in the formation of ultraluminous X-ray sources. The observational implications of such accreting systems, including X-ray emission, optical signatures, and transient phenomena, are discussed. Furthermore, we investigate the possibility of large-scale jets emanating from gas-embedded IMBHs in GCs. While several caveats and uncertainties exist, our work highlights the potential for mAGN discs to provide unique insights into IMBH demographics, accretion physics, and the dynamics of GCs. [ABSTRACT FROM AUTHOR]

The accretion of material on to a black hole modifies the properties of that hole owing to the capture of both matter and radiation. Adding matter to the hole through an accretion disc generally acts to increase the hole's spin parameter, while the capture of radiation generally provides a retarding torque. The balance between the torques provided by adding matter and radiation leads to a maximum spin parameter that can be obtained by a black hole which grows by accretion, known as the Thorne limit. In the simplest theory of thin disc accretion this Thorne limit has the value |$a_{\bullet , {\rm lim}} \simeq 0.998$|⁠. The purpose of this paper is to highlight that any modification to theories of accretion flows also modify this limiting value, and to compute precisely the modification arising from a particular extension of accretion theory: the inclusion of bright emission from within the plunging region which is sourced from the magnetohydrodynamic stresses ubiquitously observed in simulations. This extra emission further suppresses black hole spin-up and results in new, lower, limits on the final black hole spin. These limits depend on the details of the magnetic stresses acting within the plunging region, but typical values seen in simulations and observations would lower the limit to |$a_{\bullet , {\rm lim}} \simeq 0.99$|⁠ , a subtle but not negligible deviation. [ABSTRACT FROM AUTHOR]

Observations of supermassive black holes (BHs) at high redshift challenge our understanding of the evolution of the first generation of BHs in proto-galactic environments. One possibility is that they grow much more rapidly than current estimates of feedback and accretion efficiency permit. Following our previous analysis of super-Eddington accretion on to stellar-mass BHs in mini-haloes under no-feedback conditions, we now investigate whether this can be sustained when thermal feedback is included. We use four sets of cosmological simulations at sub-pc resolution with initial BH masses varying from |$1 \times 10^{3} \ \mathrm{ to} \ 6 \times 10^{4} \ {\rm M_\odot }$|⁠ , exploring a range of feedback efficiencies. We also vary the feedback injection radius to probe the threshold of numerical overcooling. We find that super-Eddington growth sustained of the order of |$\sim$| |$100 \ \rm kyr$| is possible with weak thermal feedback efficiency in all environments and moderate efficiency for two of the BHs. Trans-Eddington growth is possible for a |$3 \times 10^{3}\!\! - \!\! 6 \times 10^{3}\ {\rm M_\odot }$| BH at moderate feedback efficiencies. We discuss the effectiveness of thermal feedback in heating the gas, suppressing accretion, and driving outflows at these parameter configurations. Our results suggest that super-Eddington growth may be possible in the presence of thermal feedback for BHs formed from the first stars. [ABSTRACT FROM AUTHOR]

Quasi-periodic eruptions (QPEs) are a recently identified class of X-ray transient associated with tidal disruption events by supermassive black holes, and for which there are multiple possible explanations. In this paper, we present a simple model which requires the black hole be spinning, be misaligned with the accretion flow (both conditions of which are almost certainly met), and that the accretion rate is a few times the Eddington limit. We speculate that the resulting Lense–Thirring torques force the disc and entrained outflows to precess, leading to increased X-ray flux when the wind-cone is oriented at lower inclinations to the observer. We test the range of parameters for which this model could explain the period and brightness of the QPE events discovered thus far, and make qualitative comparisons between the observed X-ray spectra and light curves to those extracted from general relativistic radiation magnetohydrodynamic simulations. Overall, we find some areas of promising concordance, and identify challenges related to the details of current simulations. [ABSTRACT FROM AUTHOR]

Massive black hole (MBH) binaries in galactic nuclei are one of the leading sources of |${\sim}$| mHz gravitational waves (GWs) for future missions such as Laser Interferometer Space Antenna (LISA). However, the poor sky localization of GW interferometers will make it challenging to identify the host galaxy of MBH mergers absent an electromagnetic counterpart. One such counterpart is the tidal disruption of a star that has been captured into mean motion resonance with the inspiralling binary. Here we investigate the production of tidal disruption events (TDEs) through capture into, and subsequent evolution in, orbital resonance. We examine the full non-linear evolution of planar autoresonance for stars that lock into autoresonance with a shrinking MBH binary. Capture into the 2:1 resonance is guaranteed for any realistic astrophysical parameters (given a relatively small MBH binary mass ratio), and the captured star eventually attains an eccentricity |$e\approx 1$|⁠ , leading to a TDE. Stellar discs can be produced around MBHs following an active galactic nucleus episode, and we estimate the TDE rates from resonant capture produced when a secondary MBH begins inspiralling through such a disc. In some cases, the last resonant TDE can occur within a decade of the eventual LISA signal, helping to localize the GW event. [ABSTRACT FROM AUTHOR]

After decades of searching, cosmological time dilation was recently identified in the time-scale of variability seen in distant quasars. Here, we expand on the previous analysis to disentangle this cosmological signal from the influence of the properties of the source population, specifically the quasar bolometric luminosity and the rest-frame emission wavelength at which the variability was observed. Furthermore, we consider the potential influence of the evolution of the quasar population over cosmic time. We find that a significant intrinsic scatter of |$0.288 \pm 0.021$| dex in the variability time-scales, which was not considered in the previous analysis, is favoured by the data. This slightly increases the uncertainty in the results. However, the expected cosmological dependence of the variability time-scales is confirmed to be robust to changes in the underlying assumptions. We find that the variability time-scales increase smoothly with both wavelength and bolometric luminosity, and that black hole mass has no effect on the variability time-scale once rest wavelength and bolometric luminosity are accounted for. Moreover, if the standard cosmological model is correct, governed by relativistic expansion, we also find very little cosmological evolution in the intrinsic variability time-scales of distant quasars. [ABSTRACT FROM AUTHOR]

Observed low-mass galaxies with nuclear star clusters (NSCs) can host accreting massive black holes (MBH). We present simulations of dwarf galaxies (⁠|$M_{\mathrm{baryon}} \sim 0.6\!-\!2.4 \times 10^8 \rm \, M_\odot$|⁠) at solar mass resolution (⁠|$0.5\rm \, M_\odot \lt \mathit{ m}_{\mathrm{gas}} \lt 4 \rm \, M_\odot$|⁠) with a multiphase interstellar medium (ISM) and investigate the impact of NSCs on MBH growth and nuclear star formation (SF). The griffin simulation model includes non-equilibrium low temperature cooling, chemistry and the effect of H  ii regions and supernovae (SNe) from massive stars. Individual stars are sampled down to 0.08  |$\rm M_\odot$| and their non-softened gravitational interactions with MBHs are computed with the regularized ketju integrator. MBHs with masses in the range of |$10^2 \!-\! 10^5 \, \rm M_\odot$| are represented by accreting sink particles without feedback. We find that the presence of NSCs boost nuclear SF (i.e. NSC growth) and MBH accretion by funneling gas to the central few parsecs. Low-mass MBHs grow more rapidly on |$\sim 600$| Myr time-scales, exceeding their Eddington rates at peak accretion. MBH accretion and nuclear SF is episodic (i.e. leads to multiple stellar generations), coeval and regulated by SN explosions. On 40–60 Myr time-scales the first SN of each episode terminates MBH accretion and nuclear SF. Without NSCs, low-mass MBHs do not grow and MBH accretion and reduced nuclear SF become irregular and uncorrelated. This study gives the first insights into the possible co-evolution of MBHs and NSCs in low-mass galaxies and highlights the importance of considering dense NSCs in galactic studies of MBH growth. [ABSTRACT FROM AUTHOR]

We present a comprehensive spectral and timing analysis of 15 outbursts and 18 mini-outbursts from nine dynamically confirmed black hole X-ray transients with light curve and spectral data from RXTE, MAXI , and NuSTAR obtained from 1996 to 2024. Departed from the canonical fast-rise exponential decay (FRED) morphology, the most common morphology within our sample is triangular with similar rise and decay time-scale. In most outbursts, the spectral evolutions indicate the presence of limit-cycle instability, as predicted by the disc instability model (DIM). Even though almost all of the outbursts showed a similar canonical pattern, unique transition patterns are found in FRED outbursts. On the other hand, no spectral transition is found in any mini-outburst, which was observed in either hard or thermal-dominant (TD) state only. The Fe K  |$\alpha$| emission line is the most prominent feature in the hard state of the rising phase but none is found in the decay phase. Triangular outbursts are always in transition to the TD state, following a standard accretion disc, before the peak proceeds to match DIM prediction. This is unlike the FRED outburst which directly transitioned to the steep power law (SPL) state or high Eddington ratio TD state, resembling a slim accretion disc. Non-canonical spectral evolution as well as the rarity of FRED outburst in our sample, seem to add more challenges for DIM. Studying the morphology of outburst light curve may reveal more clues on the evolution of the disc instability at least during the time relevant to the burst. [ABSTRACT FROM AUTHOR]

We study the collapse of spherical cold clouds beyond black hole formation to investigate the possibility of a bounce in the in-falling matter when a critical density or pressure is reached. As a first step, we analyse the pressureless collapse in general relativity (GR), where an analytic solution exists, and demonstrate that an equivalent Newtonian solution can be derived. Such equivalence also holds for spherically symmetric perfect fluids with uniform density and non-vanishing pressure. We numerically investigate the Newtonian collapse of such clouds with masses of 5, 20, and 1000 M |$_\odot$| obeying a polytropic equation of state (EoS). By choosing EoS parameters inspired by typical neutron star conditions, we observe bounces at and above nuclear saturation density. Assuming approximate uniformity, we explore the equivalent GR behaviour of the matter during the bounce. Our findings are as follows: (i) A GR bounce occurs around the ground state of the matter, characterized by |$P = -\rho$|⁠. (ii) The GR solution differs significantly from the Newtonian result due to the presence of curvature (⁠|$k \ne 0$|⁠). (iii) Both the curvature and the ground state are crucial factors in allowing a GR bounce to occur. [ABSTRACT FROM AUTHOR]

The third Gaia data release (DR3) contains ∼170 000 astrometric orbit solutions of two-body systems located within ∼500 pc of the Sun. Determining component masses in these systems, in particular of stars hosting exoplanets, usually hinges on incorporating complementary observations in addition to the astrometry, e.g. spectroscopy and radial velocities. Several Gaia DR3 two-body systems with exoplanet, brown-dwarf, stellar, and black hole components have been confirmed in this way. We developed an alternative machine learning approach that uses only the Gaia DR3 orbital solutions with the aim of identifying the best candidates for exoplanets and brown-dwarf companions. Based on confirmed substellar companions in the literature, we use semisupervised anomaly detection methods in combination with extreme gradient boosting and random forest classifiers to determine likely low-mass outliers in the population of non-single sources. We employ and study feature importance to investigate the method's plausibility and produced a list of 20 best candidates, of which two are exoplanet candidates and another five are either very massive brown dwarfs or very low mass stars. Three candidates, including one initial exoplanet candidate, correspond to false-positive solutions where longer-period binary star motion was fitted with a biased shorter-period orbit. We highlight nine candidates with brown-dwarf companions for preferential follow-up. The companion around the Sun-like star G 15-6 could be confirmed as a genuine brown dwarf using external radial-velocity data. This new approach is a powerful complement to the traditional identification methods for substellar companions among Gaia astrometric orbits. It is particularly relevant in the context of Gaia DR4 and its expected exoplanet discovery yield. [ABSTRACT FROM AUTHOR]

Within the paradigm of nonperturbative Einstein gravity we study continuous curvature manifolds which possess de Sitter interiors and Kerr exteriors. These manifolds could represent the spacetime of rotating gravastars or other similar black hole mimickers. The scheme presented here allows for a Cn metric transition from the exactly de Sitter interior to the exactly Kerr exterior, with n arbitrarily large. Generic properties that such models must possess are discussed, such as the changing of the topology of the ergosphere from S2 to S1×S1. It is shown how in the outer layers of the transition region (the “atmosphere” as it is often called in astrophysics) the dominant/weak and strong energy conditions can be respected. However, much like in the case of its static spherically symmetric gravastar counterpart, there must be some assumptions imposed in the atmosphere for the energy conditions to hold. These assumptions turn out to not be severe. The class of manifolds presented here is expected to possess all the salient features of the fully generic case. Strictly speaking, a number of the results are also applicable to the locally anti-de Sitter core scenario, although we focus on the case of a positive cosmological constant. [ABSTRACT FROM AUTHOR]

We study thermodynamics and thermal stability of three-dimensional (3D) charged black holes (BHs) in the Brans–Dicke (BD) gravity theory. The BD field equations, which are written in the Jordan frame, are nonlinear and too complex for direct solving. Thus, by utilizing the conformal transformations (CT), we translated them to the Einstein frame, where the equations are solved easier. In the Einstein–Maxwell-dilaton (EMd) theory, the number of unknowns is one more than the unique equations. Thus, we solved this problem by using an exponential ansatz function and introduced four novel classes of 3D EMd BHs with unusual asymptotic behavior. We proved validity of the first law of BH thermodynamics (FLT), and explored thermal stability of the EMd BHs by use of the canonical ensemble method. We introduced 3D BD-Maxwell BHs by applying the inverse CT on the Einstein frame counterparts. By using the plots, we showed that our solutions can produce BD BHs without horizon, with one or two horizons. By direct calculations, we proved that thermodynamic quantities are conformal-invariant and FLT is valid for the BD BHs too. Moreover, stability properties of the BD BHs are just like those of EMd ones. [ABSTRACT FROM AUTHOR]

In this paper, we study the solutions of Einstein’s field equations in Einstein–Maxwell-dilaton gravity. By presenting the (3+1)-dimensional action in which gravity is coupled to a dilaton field, we derive the field equations. We present a new class of charged dilaton black hole solutions in Einstein–Maxwell-dilaton theory and investigate the effects of dilaton field on the properties of space–time. We show that these solutions are physical and describe spherically symmetric charged black holes. The calculated potential is Liouville type and has two rules. The exact solution of the field equations leads to the production of the metric function with three rules. By examining the physical properties of the solutions, we find the mass, charge, electric potential and temperature of charged dilaton black holes. Also, with the help of the canonical ensemble method, we study the thermodynamics and thermal stability of solutions and show the effects of dilaton and Maxwell fields on the thermodynamics of these solutions. Finally, by examining the phase transition of the solutions, we present thermal stability of the black hole in (3+1)-dimensional. [ABSTRACT FROM AUTHOR]

In this invited review, we discuss the evaporation of a black hole, with emphasis on the resulting macroscopically distinct patterns of Hawking radiation. The density matrix of this radiation can approach a pure final state in the form of a highly entangled macroscopic superposition state. We note that this exact property is exhibited in replica wormhole calculations, and also in quantum hair effects on Hawking radiation amplitudes. Finally, we revisit the information paradox (Mathur’s theorem and firewalls), showing that it can be resolved by macroscopic entanglement. [ABSTRACT FROM AUTHOR]

We report a high-redshift (⁠|$z=1.404$|⁠) tidal disruption event (TDE) candidate in SDSS J000118.70+003314.0 (SDSS J0001), which is a quasar with apparent broad Mg  ii emission line. The long-term variability in its nine-year photometric |$ugriz$| -band light curves, obtained from the SDSS Stripe82 and the PHOTOOBJALL data bases, can be described by the conventional TDE model. Our results suggest that the TDE is a main-sequence star with mass of |$1.905_{-0.009}^{+0.023}\,{\rm M_\odot }$| tidally disrupted by a black hole (BH) with mass |$6.5_{-2.6}^{+3.5}\times 10^7\,{\rm M_\odot }$|⁠. The BH mass is about 7.5 times smaller than the virial BH mass derived from the broad Mg  ii emission line, which can be explained by non-virial dynamic properties of broad emission lines from TDEs debris. Furthermore, we examine the probability that the event results from intrinsic variability of quasars, which is about |$0.009{{\ \rm per\ cent}}$|⁠ , through applications of the DRW/CAR process. Alternative explanations for the event are also discussed, such as the scenarios of dust obscurations, microlensing and accretion. Our results provide clues to support that TDEs could be detectable in broad line quasars as well as in quiescent galaxies, and to indicate the variability of some active galactic nuclei may be partly attributed to central TDEs. [ABSTRACT FROM AUTHOR]