General Relativity and Gravitation最新文献

The conference Black Holes Inside and Out marked the 50th anniversary of Hawking’s seminal paper on black hole radiance. It was clear already from Hawking’s analysis that a proper quantum gravity theory would be essential for a more complete understanding of the evaporation process. This task was undertaken in loop quantum gravity (LQG) 2 decades ago and by now the literature on the subject is quite rich. The goal of this contribution is to summarize a mainstream perspective that has emerged. The intended audience is the broader gravitational physics community, rather than quantum gravity experts. Therefore, the emphasis is on conceptual issues, especially on the key features that distinguish the LQG approach, and on concrete results that underlie the paradigm that has emerged. This is not meant to be an exhaustive review. Rather, it is a broad-brush stroke portrait of the present status. Further details can be found in the references listed.

In this paper, we consider the spherically symmetric gravitational collapse of isotropic matter undergoing dissipation in the form of heat flux, with a generalized Vaidya exterior, in the context of f(R, T) gravity. Choosing (f(R, T)=R+2lambda T), and applying the f(R, T) junction conditions on the field equations for the interior and exterior regions, we have obtained matching conditions of the matter-Lagrangian and its derivatives across the boundary. The time of formation of singularity and the time of formation of apparent horizon have been determined and constraints on the integration constants are examined for which the final singularity is hidden behind the horizon.

Various generalizations of the scalar, axisymmetric “horizon hair” for extremal black holes have recently appeared in the literature. In this paper, we propose an expression for a non-axisymmetric gravitational “charge” and its potentially observable imprint at a finite distance from the horizon (Ori-coefficient) in extremal Kerr black hole backgrounds. Using a hyperboloidal foliation, we offer strong and robust numerical evidence for the potential existence of this horizon hair and its properties. Specifically, we consider the time evolution of horizon penetrating, quadrupolar and (subdominant) octupolar gravitational perturbations with compact support on extremal Kerr (EK) spacetime. We do this by numerically solving the Teukolsky equation and determining the conserved charge values on the horizon and at a finite distance from the black hole.

In this paper, we consider families of solutions for excited states of Proca stars in spherical symmetry. We focus on the first two excited configurations and perform a series of fully non-linear dynamical simulations in order to study their properties and stability. Our analysis reveals that excited Proca stars are always unstable against even very small perturbations, and their dynamical evolution can lead to three different final states: collapse to a black hole, dissipation, or migration to a different configuration in the ground state. We find that migration to the ground state can only occur in a small region of the parameter space of solutions with negative binding energy.

In recent papers, Fuentealba, Henneaux, and Troessaert (FHT) gave definitions for supertranslation invariant Lorentz charges in the ADM Hamiltonian formalism and showed that their definitions match with the Chen, Wang, Yau (CWY) definitions of Lorentz charges at null infinity which are free from “supertranslation ambiguities”. In this brief note, motivated by the analysis of FHT, we write expressions for the supertranslation invariant Lorentz charges in Beig–Schmidt variables at spacelike and timelike infinity. We present calculations, building upon the work of Compère, Gralla, and Wei (CGW), to show that our expressions for supertranslation invariant Lorentz charges match the CWY definitions at null infinity.

The interaction of black holes with classical fields can lead to many interesting phenomena such as black-hole superradiance and the superradiant instability. The existence of these effects has been shown to have implications for beyond Standard Model particles that could explain dark matter, namely ultralight bosonic fields. In this note I give a historical account of this topic and briefly go through some recent developments. I conclude with some personal reflections on the importance of constraining simple dark matter models, even if such models may ultimately be the incorrect description of nature.

The saddle point approximation to formal quantum gravitational partition functions has yielded plausible computations of horizon entropy in various settings, but it stands on shaky ground. In this paper we visit some of that shaky ground, address some foundational questions, and describe efforts toward a more solid footing. We focus on the case of de Sitter horizon entropy which, it has been argued, corresponds to the dimension of the Hilbert space of a ball of space surrounded by the cosmological horizon.

We construct non-static adiabatic axisymmetric structures embedded in an asymptotically (Lambda )CDM universe from given solutions of the Poisson’s equation of Newtonian gravity, using a particular form of the metric in isotropic coordinates. The approach is used in building of a razor-thin disk source made of perfect fluid for the McVittie metric, a system composite by a Plummer-type perfect fluid razor-thin disk surrounded by an halo also of perfect fluid, and a model of Miyamoto–Nagai-type anisotropic fluid thick disks, embedded in an asymptotic (Lambda )CDM universe. In the especial case of spherical symmetry, we also present a family of models of expanding anisotropic thick spherical shells. Moreover, the geodesic motion of test particles in stable circular orbits around of the structures, the fulfilment of the energy conditions and principal stresses (pressure) are analyzed.

In this article, we theoretically construct a (2 + 1)-dimensional rotating thin shell wormhole using the Darmois-Israel junction formalism. This thin shell wormhole whose validity has been checked by analyzing the energy conditions, specifically, the weak and null energy conditions, is actually constructed by cutting and pasting two rotating hairy black hole spacetimes in (2+1)-dimensions. We further discuss different physical features of the constructed wormhole, viz., the nature of the gravitational field, the equation of state at the throat, and the time evolution of the throat radius. We also analyze the stability of the thin shell wormhole by investigating the equation of motion under small perturbations.

Do compact objects other than black holes and neutron stars exist in the universe? Do all black holes conform with the predictions of Einstein’s General Relativity? Do classical black holes exist at all? Future gravitational-wave observations and black-hole imaging might shed light on these foundational questions and deepen our understanding of the dark cosmos.