A5016501308- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Relativity and Gravitational Theory
- Quantum Electrodynamics and Casimir Effect
- Noncommutative and Quantum Gravity Theories
- Experimental and Theoretical Physics Studies
- Advanced Thermodynamics and Statistical Mechanics
- Adaptive optics and wavefront sensing
- Mechanics and Biomechanics Studies
- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Heat Transfer Mechanisms
- Gas Dynamics and Kinetic Theory
- Radiative Heat Transfer Studies
- Streptococcal Infections and Treatments
- Gamma-ray bursts and supernovae
- Laser-Plasma Interactions and Diagnostics
- Mathematical and Theoretical Analysis
- Superconducting Materials and Applications
- Particle Accelerators and Free-Electron Lasers
- Astronomical Observations and Instrumentation
Daido University
2014-2024
National Astronomical Observatory of Japan
2024
Harvard University Press
2024
Yamaguchi University
2014
Kyoto University
2000-2002
Osaka City University
2002
The mechanical first law (MFL) of black hole spacetimes is a geometrical relation which relates variations the mass parameter and horizon area. While it well known that MFL an asymptotic flat equivalent to its thermodynamical law, however we do not know detail with cosmological constant possess event horizons. This paper aims formulate two-horizon spacetimes. For this purpose, try include effects two horizons in MFL. To so, make use Iyer–Wald formalism extend regard as independent variables...
Gravitational redshift in the Galactic Center General relativity predicts that light emitted by an object a strong gravitational field—for example, close to black hole—should be shifted longer wavelengths. This does not exist Newtonian theory of gravity. Do et al. monitored position and spectrum star S0-2 as it passed Sagittarius A*, supermassive hole at center Milky Way. Around closest part S0-2's 16-year orbit, they detected effect on its spectrum. These results are more consistent with...
Direct observation of black holes is one the grand challenges in astronomy. If there are supercompact objects which possess unstable circular orbits photons, however, it may be difficult to distinguish them from by observing photons. As a model objects, we consider gravastar (gravitational-vacuum-star) was originally proposed Mazur and Mottola. For definiteness, adopt spherical thin-shell developed Visser Wiltshire, connects interior de Sitter geometry exterior Schwarzschild geometry. We...
Searching for space-time variations of the constants Nature is a promising way to search new physics beyond general relativity and standard model motivated by unification theories models dark matter energy. We propose variation fine-structure constant using measurements late-type evolved giant stars from S star cluster orbiting supermassive black hole in our Galactic Center. A measurement difference between distinct absorption lines (with different sensitivity fine structure constant) leads...
We calculate the quantum radiation power of black holes which are asymptotic to Einstein–de Sitter universe at spatial and null infinities. consider two limiting mass accretion scenarios, no significant accretion. find that strongly depends on not only condition but also scenario. For case, we Einstein–Straus solution, where a hole constant resides in dust Friedmann universe. negative cosmological correction besides expected redshift factor. This is given terms cubic root ratio size horizon,...
We consider the periapsis shifts of bound orbits stars on static clouds around a black hole. The background spacetime is constructed from Schwarzschild hole surrounded by and spherically symmetric self-gravitating system massive particles, which satisfies all standard energy conditions physically models gravitational effect dark matter distribution nonrotating Using nearly circular stars, we obtain simple formula for precession rate. This explicitly shows that rate determined positive...
We consider one model of a black hole radiation, in which the equation motion matter field is modified to cut off high frequency modes. The spectrum has already been analytically derived low range, resulted Planckian distributin Hawking temperature. On other hand, it numerically shown that its deviates from thermal range. In this paper, we derive form deviation Our result can qualitatively explain nature calculated spectrum. origin clarified by simple discussion.
We study the null geodesics in a static circularly symmetric (SCS) black hole spacetime which is solution $(2+1)$-dimensional massive gravity proposed by Bergshoeff, Hohm and Townsend (BHT gravity). obtain analytic solutions for geodesic equation SCS background find explicit form of deflection angles. see that various values impact parameter, angle can be positive, negative or even zero this spacetime. The indicates repulsive behavior comes from gravitational hair parameter most...
A numerical simulation of fluid flows in a Laval nozzle is performed to observe formations acoustic black holes and the classical counterpart Hawking radiation under realistic setting laboratory experiment. We determined temperature hole from obtained data. Some noteworthy points analyzing experimental data are clarified through our simulation.
The existing thermodynamics of the cosmological horizon in de Sitter spacetime is established micro-canonical ensemble, while black hole horizons canonical ensemble. Generally ordinary and statistical mechanics, both ensembles yield same equation state for any thermodynamic system. This implies existence a formulation based on paper reproduces procedure as follows: We put spherical wall at center spacetime, which has negligible mass perfectly reflects Hawking radiation coming from horizon....
This paper consists of three steps. In the first, we prove that Bekenstein-Hawking entropy is unique expression black hole entropy. Our proof constructed in framework thermodynamics without any statistical discussion. second, intrinsic properties quantum mechanics are shown, which justify Boltzmann formula to yield a mechanics. These clarify conditions, one necessary and others sufficient for validity formula. third, by combining above results, find reasonable suggestion from conditions...
The Black Hole Explorer (BHEX) is a next-generation space very long baseline interferometry (VLBI) mission concept that will extend the ground-based millimeter/submillimeter arrays into space. mission, closely aligned with science priorities of Japanese VLBI community, involves an active engagement this community in development resulting formation Japan Consortium. Here we present current vision for ranging from scientific objectives to instrumentation. Consortium anticipates wide range...
The Black Hole Explorer (BHEX) is a next-generation space very long baseline interferometry (VLBI) mission concept that will extend the ground-based millimeter/submillimeter arrays into space. mission, closely aligned with science priorities of Japanese VLBI community, involves an active engagement this community in development resulting formation Japan Consortium. Here we present current vision for ranging from scientific objectives to instrumentation. Consortium anticipates wide range...
It seems to be a common understanding at present that, once event horizons are in thermal equilibrium, the entropy-area law holds inevitably. However no rigorous verification is given such very strong universality of multi-horizon spacetimes. Then, based on thermodynamically consistent and discussion, this paper suggests an evidence breakdown for Schwarzschild-de Sitter spacetime, which temperatures different. The outline as follows: We construct carefully "two equilibrium systems"...
The so-called black hole shadow is a dark region which expected to appear in fine image of optical observation holes. It essentially an absorption cross section the hole, and boundary determined by unstable circular orbits photons (UCOP). If there exists compact object possessing UCOP but no horizon, it can provide us with same as holes, detection cannot be direct evidence existence. This paper examines whether or not such objects exist under some suitable conditions. We investigate...
The ratio of total mass $M$ to surface radius $R$ spherical perfect fluid ball has an upper bound, $M/R < B$. Buchdahl obtained $B = 4/9$ under the assumptions; non-increasing density in outward direction, and barotropic equation states. Barraco Hamity decreased Buchdahl's bound a lower value 3/8$ $(< 4/9)$ by adding dominant energy condition assumptions. In this paper, we further decrease Barraco-Hamity's \simeq 0.3636403$ 3/8)$ subluminal (slower-than-light) sound speed. our analysis,...
The star S0-2, orbiting the Galactic central massive black hole candidate Sgr A*, passed its pericenter in May 2018. This event is first chance to detect general relativistic (GR) effect of a hole, free from non-gravitational physics. observable GR evidence difference between redshift and Newtonian photons coming S0-2. Within present observational precision, 1st post-Newtonian (1PN) detectable. In this paper, we give theoretical analysis time evolution 1PN evidence, under presupposition that...
We propose a theoretical principle to measure the mass, spin, and direction of spin axis Kerr black holes (BHs) through observing 2 quantities spinning strong gravitational lens effect BHs. Those observable are generated by light rays emitted at same time source near BH: primary secondary that reach distant observer, respectively, earliest temporally. The delay between detection times ratio observed specific fluxes those quantities. Rigorously, our proposal is applicable single burst-like...
When a black hole is in an empty space on which there no matter field except that of the Hawking radiation (Hawking field), then evaporates and entropy decreases. The generalised second law guarantees increase total whole system consists field. That is, faster than decrease entropy. In naive sense, one may expect due to self-interaction among composite particles field, "self"-relaxation results increase. Then, when consider non-self-interacting as it obvious self-relaxation does not take...
We consider a model of an inhomogeneous universe including massless scalar field, where the inhomogeneity is assumed to consist many black holes. This can be constructed by following Lindquist and Wheeler, which has already been investigated without field show that averaged scale factor coincides with Friedmann model. In this work we construct assume are given those field. All our calculations carried out in framework Brans-Dicke gravity. constructing universe, define mass hole expanding...
When a black hole evaporates, there arises net energy flow from into its outside environment (heat bath). The existence of means that the thermodynamic state whole system, which consists and heat bath, is in nonequilibrium state. Therefore, order to study detail evaporation process, effects should be taken account. Using thermodynamics has been formulated recently, this paper shows following: (1) Time scale bath becomes shorter than an empty space (a situation without bath), because effect...
During the next closest approach of orbiting star S2/S0-2 to Galactic supermassive black hole (SMBH), it is estimated that RV uncertainties ~ 10 km/s allow us detect post-Newtonian effects throughout 2018. To evaluate an achievable uncertainty in and its stability, we have carried out near-infrared, high resolution (R 20,000) spectroscopic monitoring observations S2 using Subaru telescope near-infrared spectrograph IRCS from 2014 2016. The Br-gamma absorption lines are used determine RVs S2....
The Hawking radiation forms the essential basis of black hole thermodynamics. thermodynamics denotes a nice correspondence between kinematics and laws ordinary thermodynamics, but has been so far considered only in an asymptotically flat case. Does such rely strongly on feature gravity vanishing at infinity? In order to resolve this question, it should be for first extend case with dynamical boundary condition like expanding universe. Therefore universe is discussed paper. As concrete model...