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We present a detailed analysis of the thermodynamics of black holes in flat spacetime with Eddington inspired Born-Infeld theory of gravity. The thermodynamic properties are obtained through the surface gravity method that is well known in black hole mechanics. We analyse the stability of the black holes configuration through the property of its specific heat. It is found that electrically charged black holes in EiBI gravity are unstable, and this may be related to the thermodynamic instability of flat spacetime itself. [ABSTRACT FROM AUTHOR]

In this paper, we examine the geodesic equation around a global monopole within an asymptotically flat black hole using Eddington-inspired Born-Infeld (EiBI) theory of gravity. In particular, we study massive particle motion around the black hole.We find that the effective potential and radial force for this massive particle depend on the coupling constant of EiBI gravity. [ABSTRACT FROM AUTHOR]

The article focuses on research into the process by which astrophysical jets emitted from Active Galactic Nuclei (AGN) are formed. It states that it is believed astrophysical jets require magnetized accreting plasma and a rotating black hole and suggests plasma embedded in a black hole's magnetic field could sometimes be considered a collection of non-linear strings, or flux tubes. It comments on the use of simulations to show the formation of collimated bubble-structured relativistic jets.

We review recent progress in our understanding of the nature of gamma ray bursts (GRBs) and in particular, in the relationship between the short GRBs and the long GRBs. The coincidental occurence of a GRB with a Supernova (SN) is explained within the Induced Gravitational Collapse (IGC) paradigm, following the sequence: 1) an initial binary system consists in a compact Carbon-Oxygen (CO) core and a NS; 2) the CO core explodes giving origin to a SN and part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a BH giving rise to a long GRB; 3) a new NS is generated by the SN as a remnant. The observational consequences of this scenario are outlined. The first example of a short GRB is given. [ABSTRACT FROM AUTHOR]

The last ten years have seen significant progress have seen major improvements in our ability to observe and characterize the X-ray emission from black hole systems. In particular, the arrival of a new generation of X-ray satellites that combine large collection area, broad energy response, and flexible monitoring ability (starting with RXTE, BeppoSax, INTEGRAL, and culminating with Suzaku and Swift) finally enables us to begin to uniquely probe the rapidly changing physical conditionsin the plasma near a black hole, on timescales from milliseconds to years. I review our current understanding of these conditions, with an eye towards stimulating discussions with laboratory colleagues who have access to (still) much better diagnostics. [ABSTRACT FROM AUTHOR]

We consider dark matter annihilation in the gravitational field of a black hole. We obtain exact distribution function of the infalling dark matter particles, and compute the resulting flux and spectra of gamma rays coming from the objects. It is shown that the dark matter density significantly increases near a black hole. Particle collision energy becomes very high affecting relative cross-sections of various annihilation channels. We also discuss possible experimental consequences of these effects. [ABSTRACT FROM AUTHOR]

The gravity-scalar field system in spherical symmetry provides a natural setting for exploring gravitational collapse and its aftermath in quantum gravity. In a canonical approach, we give constructions of the constraint and Hamiltonian operators. Matter-gravity entanglement is an inherent feature of physical states, whether or not there is a black hole. Matter fields alone are an open system with a non-unitary evolution. However, if there is a successful theory of quantum gravity, there is no information loss. [ABSTRACT FROM AUTHOR]

It is shown that Kundt’s metric for vacuum cannot be constructed when two-dimensional space-like sections of null hypersurfaces are compact, connected manifolds with no boundary unless they are tori or spheres, i.e. higher genus g>=2 is excluded by vacuum Einstein equations. The so-called basic equation (resulting from Einstein equations) is examined. This is a non-linear PDE for unknown covector field and unknown Riemannian structure on the two-dimensional manifold. It implies several important results derived in [3]. It arises not only for Kundt’s class but also for degenerate Killing horizons [2] and vacuum degenerate isolated horizons [1, 7]. [ABSTRACT FROM AUTHOR]

We review the recent noticeable progresses in black hole physics focusing on the up-coming super-collider, the LHC. We discuss the classical formation of black holes by particle collision, the greybody factors for higher dimensional rotating black holes, the deep implications of black hole physics to the ‘energy-distance’ relation, the security issues of the LHC associated with black hole formation and the newly developed Monte-Carlo generators for black hole events. [ABSTRACT FROM AUTHOR]

We found that neutrino-dominated accretion flows have both a maximal and a minimal possible mass accretion rate at their each radius. This may be suggestive of an interpretation for the origin of X-ray flares observed in gamma-ray bursts. [ABSTRACT FROM AUTHOR]

The possibility of the particle creations in the strong magnetic environments of GRB central region is demonstrated in two examples. The pair creation of neutrinos with magnetic moment is shown to be possible for the strong magnetic field stronger than critical value, provided the direct coupling of with electromagnetic field through Pauli interaction. The production rate near critical field is estimated w∼1030/m3 s(mv10-2 eV)4 for the neutrino with mass mv and with magnetic moment of the present experimental upper bound. The possible non-force-free nature near the equatorial plane of the rotating black hole can provide a local frame where the electric field is dominant over magnetic field. Near the equatorial plane, it is demonstrated that electron- positron pair creations is possible via Schwinger process for a slowly rotating magnetic field, ΩF<Ω-. [ABSTRACT FROM AUTHOR]

Since it was first discovered in 1963 the Kerr metric has been used by relativists as a test-bed for conjectures on worm-holes, time travel, closed time-like loops, and the existence or otherwise of global Cauchy surfaces. More importantly, it has also used by astrophysicists to investigate the effects of collapsed objects on their local environments. These two groups of applications should not be confused. Astrophysical Black Holes are not the same as the Kruskal solution and its generalisations. [ABSTRACT FROM AUTHOR]

We revisit the vertical structure of black hole accretion disks in spherical coordinates. By comparing the advective cooling with the viscous heating, we show that advection-dominated disks are geometrically thick, i.e., with the half-opening angle Δθ>2π/5, rather than slim as supposed previously in the literature. We suggest that such advection-dominated thick disks around stellar mass black holes may account for the brightest ultraluminous X-ray sources. [ABSTRACT FROM AUTHOR]

We investigate the properties of the shock waves for a rotating accretion flow around a spinning black hole (BH) in presence of synchrotron cooling. We present all possible accretion solutions. We show that global accretion shock solutions exist for a wide range of flow parameters. We separate the region of the parameter space for steady and oscillating shocks which gradually shrinks as cooling is increased. We also find that shock fronts move closer to the BH for enhanced cooling efficiency which could be the source of high frequency quasi-periodic oscillations around the rotating black holes at higher accretion rate. [ABSTRACT FROM AUTHOR]

The gravitational collapse of a star is an important issue both for general relativity and astrophysics, which is related to the well known “frozen star” paradox. Following the seminal work of Oppenheimer and Schneider (1939), we present the exact solution for two dust shells collapsing towards a pre-existing black hole. We find that the inner region of the shell is influenced by the property of the shell, which is contrary to the result in Newtonian theory and and the clock inside the shell becomes slower as the shell collapses towards the pre-existing black hole. This result in principle may be tested experimentally if a beam of light travels across the shell. We conclude that the concept of the “frozen star” should be abandoned, since matter can indeed cross a black hole’s horizon according to the clock of an external observer. Since matter will not accumulate around the event horizon of a black hole, we predict that only gravitational wave radiation can be produced in the final stage of the merging process of two coalescing black holes. Our results also indicate that for the clock of an external observer, matter, after crossing the event horizon, will never arrive at the “singularity” (i.e. the exact center of the black hole). [ABSTRACT FROM AUTHOR]

We perform fully general relativistic simulations of collapse of a rapidly rotating massive stellar core to a ’collapsar’ black hole (BH) surrounded by a massive, hot accretion disk with simplified microphysics. We continue the simulation until the system consisting of the BH and the disk has relaxed to a quasi-stationary state. A novel mechanism found is that strong shock waves are formed at the inner part of the disk after the formation of the BH. These shock waves propagate mainly along the rotation axis, heating the disk and sweeping materials around the rotational axis, and thereby forming a low density region. The temperature of the disk is high enough for copious neutrino emission. All these features indicate that the direct formation of a rapidly rotating BH is a promising source of LGRBs. [ABSTRACT FROM AUTHOR]

This paper reviews the recent progress in the research of equation of state of dense matter for supernova simulations. The equation of state plays an important role to clarify the mechanism of core-collapse supernovae, the formation of compact objects and the properties of supernova neutrinos. We describe the problems of explosion mechanism in current supernova simulations, putting emphasis on the equation of state. We discuss also the topics on the birth of neutron stars (or black holes) and the associated neutrino bursts, which reflect the properties of dense matter. [ABSTRACT FROM AUTHOR]

We have used the Novikov-Thorne thin disk model to fit the continuum X-ray spectra of three transient black hole X-ray binaries in the thermal state. From the fits we estimate the dimensionless spin parameters of the black holes to be: 4U 1543–47, a∗≡a/M = 0.7–0.85; GRO J1655–40, a∗ = 0.65–0.8; GRS 1915+105, a∗ = 0.98–1. We plan to expand the sample of spin estimates to about a dozen over the next several years. Some unresolved theoretical issues are briefly discussed. [ABSTRACT FROM AUTHOR]

Some of the latest results of the simulation for the merger of black hole (BH)-neutron star (NS) binaries in full general relativity is presented. As the initial condition, we prepare a quasicircular state in which the BH is modeled by a moving puncture with no spin. The Γ-law equation of state with Γ = 2 and irrotational velocity field are used for modeling the NS. The BH mass is chosen to be ≈4 M⊙, whereas the rest-mass of the NS is ≈1.4 M⊙ and the radius is ≈13 km. The NS is tidally disrupted near the innermost stable orbit but more than ∼90% of the material is quickly swallowed into the BH and the resultant disk mass is ≈0.1 M⊙. The thermal energy of the material in the disk increases by the shock heating occurred in the collision between the spiral arms. Our results indicate that the merger between a low-mass BH and its companion NS may form a central engine of short-gamma-ray bursts. Gravitational waveforms are also presented. We find that the amplitude of gravitational waves quickly decreases after the tidal disruption and the amplitude of the quasinormal mode ringing is small. [ABSTRACT FROM AUTHOR]

Recent observations on both microquasars and AGNs with radio and X-ray telescopes have revealed remarkable radio/X-ray correlation of these objects. Because the radio and X-ray emissions are mainly emitted from jet and accretion flow, the radio/X-ray correlation can be used to probe the accretion-jet physics in these accreting black hole systems. Using a uniform broad line SDSS AGN sample, we derived the black hole fundamental plane relationship among the 1.4 GHz radio luminosity (Lr), 0.1–2.4 keV X-ray luminosity (LX), and black hole mass (M). We found from our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington luminosity scaled X-ray and radio luminosities for the radio quiet subsample. In addition, we noticed that radio-loud AGNs have steeper power-law slope in the radio/X-ray correlation than radio-quiet AGNs. This is mainly due to the different origin of X-ray emissions in radio-loud and radio-quiet AGNs. We discussed the theoretical interpretations of these results and the similarity in the radio/X-ray correlation between microquasars and AGNs. [ABSTRACT FROM AUTHOR]

It has been well known that in the point of view of a distant observer, all in-falling matter to a black hole (BH) will be eventually stalled and “frozen” just outside the event horizon of the BH, although an in-falling observer will see the matter falling straight through the event horizon. Thus in this “frozen star” scenario, as distant observers, we could never observe matter falling into a BH, neither could we see any “real” BH other than primordial ones, since all other BHs are believed to be formed by matter falling towards singularity. Here we first obtain the exact solution for a pressureless mass shell around a pre-existing BH. The metrics inside and interior to the shell are all different from the Schwarzschild metric of the enclosed mass, meaning that the well-known Birkhoff Theorem can only be applied to the exterior of a spherically symmetric mass. The metric interior to the shell can be transformed to the Schwarzschild metric for a slower clock which is dependent of the location and mass of the shell; we call this Generalized Birkhoff Theorem. Another result is that there does not exist a singularity nor event horizon in the shell. Therefore the “frozen star” scenario is incorrect. We also show that for all practical astrophysical settings the in-falling time recorded by an external observer is sufficiently short that future astrophysical instruments may be able to follow the whole process of matter falling into BHs. The distant observer could not distinguish between a “real” BH and a “frozen star”, until two such objects merge together. It has been proposed that electromagnetic waves will be produced when two “frozen stars” merge together, but not true when two “real” bare BHs merge together. However gravitational waves will be produced in both cases. Thus our solution is testable by future high sensitivity astronomical observations. [ABSTRACT FROM AUTHOR]

In the Relativistic Theory of Gravitation, space-time is Minkowskian, and gravitation is a physical field, next to electromagnetism. The bimetric coupling of Riemann and Minkowski metrics allows to defines a unique, local gravitational energy density. The case of a positive cosmological constant is considered. For cosmology, the ΛCDM model is covered, while there appears a form of inflation at early times. Furthermore, both the total energy and the zero point energy vanish. Within this theory an exact solution is presented for the interior of supermassive black holes (M*∼108M⊙. They are consistent with a Bose-Einstein condensates of densely packed H-atoms. The solution is regular everywhere with a specific shape at the origin. The redshift at the horizon is finite but large, z∼1014M*/M. The problem is exactly and self-consistently solved within a quantum field theoretic approach for the matter. Its direct back-reaction on the metric is 100%. In the BEC ground state, the binding energy equals 71% of the rest energy of the constituting matter. Extension to finite temperatures reveals a T3/2 decay of the entropy. At T = 0 the black hole does not radiate. [ABSTRACT FROM AUTHOR]

The production of mini black holes due to large extra dimensions is a speculative but possible scenario. We survey estimates for di-jet suppression, and multi-mono-jet emission due to black hole production. We further look for a possible sub-scenario which is the formation of a stable or meta-stable black hole remnant (BHR). We show that the beauty of such objects is, that they are relatively easy to observe, even in the early phase of LHC running. [ABSTRACT FROM AUTHOR]

I describe several broad features of a programme to understand gravity as an emergent, long wavelength, phenomenon (like elasticity) and discuss one concrete framework for realizing this paradigm in the backdrop of several recent results. [ABSTRACT FROM AUTHOR]

In the series of papers by Ida, Oda and Park, the complete description of Hawking radiation to the brane localized Standard model fields from mini black holes in the low energy gravity scenarios are obtained. In this proceedings, we briefly review what we have learned in those papers. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We consider how to search for complex inspiral chirps when constrained by realistic computing resource limits. We briefly compare three alternate search strategies based on different template allocations for the initial search step: 1. Allocating templates uniformly throughout LISA’s most sensitive frequency band from .003 Hz to .01 Hz; 2. Allocating all templates to a single frequency at the entrance to this band (.003 Hz); 3. Allocating all templates to a single frequency at the exit from this band (.01 Hz). We argue that a search strategy focusing most resources on a single frequency is favored by: the ease of ‘following’ a signal once it has been found versus the difficulty of finding it initially; the shape of the LISA sensitivity curve; and the template-count limits imposed by attainable computational resources. We devise a combined strategy that uses multiple search techniques, beginnig with a single-frequency template-allocation method. This combined strategy is quite powerful; it can detect inspirals that would be missed by using only the uniform template allocation search strategy with the same total template count. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We investigate highly damped quasinormal mode of single-horizon black holes motivated by its relation to the loop quantum gravity. Using the WKB approximation, we show that the real part of the frequency approaches the value conjectured by Medved et al. and Padmanabhan for dilatonic black hole. It is surprising since the area specrtum of the black hole determined by the Bohr’s correspondence principle completely agrees with that of Schwarzschild black hole for any values of the electromagnetic charge or the dilaton coupling. We discuss its generality for single-horizon black holes and the meaning in the loop quantum gravity. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We describe the stationary accretion of dark energy around a black hole. Solution for a stationary spherically symmetric accretion of the relativistic perfect fluid with an arbitrary equation of state onto the Schwarzschild black hole is presented. This solution is a generalization of Michel solution and applicable to the problem of dark energy accretion. It is shown that accretion of phantom energy is accompanied with the gradual decrease of the black hole mass. Masses of all black holes tend to zero in the phantom energy universe approaching to the Big Rip. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present the recent progress of researches to clarify the phenomena of core-collapse supernovae in the light of the advance in nuclear physics. We focus on the table of equation of state (EOS), which is one of the key ingredients in supernovae, in the relativistic many body framework constrained by the data of unstable nuclei. We apply the relativistic EOS table to the numerical simulations of supernovae following the gravitational collapse of massive stars to examine whether the explosion is triggered. We discuss the influence of the EOS on the core-collapse, bounce, the revival of shock wave and the birth of proto-neutron stars. In the case of more massive stars, we demonstrate that the EOS is crucial to predict the rapid formation of black hole. The properties of neutrino burst toward the black hole formation is sensitive to the EOS accordingly and can be used as a probe of dense matter by the observation of supernova neutrinos at the terrestrial neutrino detectors. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, I summarise the recent results of our study on the core-collapse supernova and related phenomena. Among the issues addressed are (1) long-term ID simulations of core-collapse supernovae, (2) global asymmetry of supernova, and (3) collapse of more massive stars and neutrino signals. In the first topic, I report our latest 1D simulations for more than a second after the bounce and demonstrate that the difference of EOS’s manifests itself more clearly in the later phase of the core collapse. In the second part, I discuss hydrodynamic instabilities as a possible cause for the global asymmetry that may be a generic feature of core-collapse supernova. The mode analysis of the non-spherical instability of the standing accretion shock is presented. Inelastic scatterings of neutrino on nuclei are also discussed in this context. Finally, I mention the gravitational collapse of more massive stars which will produce not a neutron star but a black hole. Particular attention is paid to the neutrino signals from these phenomena as a probe of hot dense matter. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have performed a fully three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulation of jet formation from a thin accretion disk around a Schwarzschild black hole with a free-falling corona. The initial simulation results show that a bipolar jet (velocity ≈ 0.3c) is created as shown by previous two-dimensional axisymmetric simulations with mirror symmetry at the equator. The 3-D simulation ran over one hundred light-crossing time units (τS = rS/c where rS ≡ 2GM/c2) which is considerably longer than the previous simulations. We show that the jet is initially formed as predicted due in part to magnetic pressure from the twisting the initially uniform magnetic field and from gas pressure associated with shock formation in the region around r = 3rS. At later times, the accretion disk becomes thick and the jet fades resulting in a wind that is ejected from the surface of the thickened (torus-like) disk. It should be noted that no streaming matter from a donor is included at the outer boundary in the simulation (an isolated black hole not binary black hole). The wind flows outwards with a wider angle than the initial jet. The widening of the jet is consistent with the outward moving torsional Alfvén waves (TAWs). This evolution of disk-jet coupling suggests that the jet fades with a thickened accretion disk due to the lack of streaming material from an accompanying star. We have also calculated the free-free emission from a disk/outflow near a rotating black hole using our axisymmetric GRMHD simulation using a covariant radiative transfer formulation. Our calculation shows radiation from a shock, and hence the disk-jet coupling region is observable. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

By adopting the correct vertical gravitational force in studies of thermal equilibrium solutions, we find that there exists a maximal possible accretion rate for each radius in the outer region of optically thick accretion flows, such that only the inner regions of these flows can possibly take the form of slim disks. [ABSTRACT FROM AUTHOR]

Neutrino-cooled hyperaccretion disks around stellar mass black holes are plausible candidates for the central engine of gamma-ray bursts. We calculate the one-dimensional structure and the annihilation luminosity of such disks. The resulting neutrino annihilation luminosity is still likely to be adequate for gamma-ray bursts, and it is ejected mainly from the inner region of the disk and has an anisotropic distribution. [ABSTRACT FROM AUTHOR]

We study the fate of core-collapse supernovae from the massive stars by numerical simulations of neutrino-radiation hydrodynamics. We follow the long term evolution over 1 sec after the core bounce from the initial gravitational collapse to examine the explosion mechanism and to reveal the formation of neutron star and black hole. We explore the effects of equation of state (EOS) in these simulations by adopting the two sets of realistic EOS for supernovae. For the case of a 40M⊙ star, we find that the formation of black hole occurs in different timing depending on the softness of EOS and resulting properties of emergent neutrinos appear differently from ordinary supernova neutrinos. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Population III stars are thought to be very massive stars. However, their properties are not clarified yet. In this research, we investigate the features of magnetorotational dynamics of such stars with computer simulations. We find jet-like explosion in a few models and reveal what type of initial model undergo explosion. In addition, we inquire features of newborn black holes as a remnant of core-collapse. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]