Vaidya Metric Research Articles

Thermodynamics with conformal Killing vector in the charged Vaidya metric

We investigate the charged Vaidya spacetime with conformal symmetry by classifying the horizons and finding its connection to Hawking temperature. We find a conformal Killing vector whose existence requires the mass and electric charge functions to be proportional, as well as linear in time. Solving the Killing equations for the conformally transformed metric from the linear charged Vaidya metric yields the required form of the conformal factor. From the vanishing of the norm of the conformal Killing vector, we find three conformal Killing horizons which, under the transformation, are mapped to the Killing horizons of the associated static spacetime, if the spherical symmetry is maintained. We find that the conformal factor is not uniquely determined, but can take any function of the ratio of the radial coordinate to the dynamical mass. As an example, we illustrate a static spacetime with our choice of the conformal factor and explicitly show that the surface gravity of the conformal Killing horizons, which is conformally invariant, yield the expected Hawking temperature in the static spacetime. This static black hole spacetime contains a cosmological horizon, but it is not asymptotically de Sitter. We also investigate the case when the mass parameter is equal to the constant electric charge. While in this case the standard pair of horizons, the loci of the time component of the metric, degenerate, the conformal Killing horizons do not degenerate. This therefore leads to a non-zero Hawking temperature in the associated static spacetime.

Shearing, dissipative collapse influenced by an equation of state

We make use of a perturbative scheme to implement an equation of state guided, gravitational collapse of a compact stellar object. General relativity is used in which a spherically symmetric spacetime in Schwarzschild coordinates is assumed with an appropriate energy–momentum tensor allowing for heat-flux. For the dissipative collapse, the Vaidya metric is used for the exterior with the required matching to the interior metric. An initial static configuration is firstly set up and then a linear equation of state is used to assist in closing the system of equations for the perturbative part. The resulting model is physically viable and the effect of shearing stresses are examined in terms of the luminosity. We see that shearing augments the luminosity and duration of the collapse process. Further improvements in the modelling process are believed possible by using more sophisticated gravitational potentials and equations of state.

Spherical doubly warped spacetimes for radiating stars and cosmology

Spherically symmetric spacetimes are ambient spaces for models of stellar collapse and inhomogeneous cosmology. We obtain results for the Weyl tensor and the covariant form of the Ricci tensor on general doubly warped (DW) spacetimes. In a spherically symmetric metric, the Ricci and electric tensors become rank-2, built with the metric tensor, a velocity vector field and its acceleration. Their structure dictates the general form of the energy-momentum tensor in the Einstein equations in DW spherical metrics. The anisotropic pressure and the heat current of an imperfect fluid descend from the gradient of the acceleration and the electric part of the Weyl tensor. For radiating stellar collapse with heat flow, the junction conditions of the doubly warped metric with the Vaidya metric are reviewed, with the boundary condition for the radial pressure. The conditions for isotropy simply accomodate various models in the literature. The anisotropy of the Ricci tensor in the special case of spherical GRW space-times (geodesic velocity), gives Friedmann equations deviating from standard FRW cosmology by terms due to the electric tensor. We introduce “perfect 2-scalars” to discuss f(R) gravity with anisotropic fluid source in a doubly warped spacetime, and show that the new geometric terms in the field equations do not change the tensor structure of the fluid energy-momentum tensor.

The Vaidya metric: Expected and unexpected traits of evaporating black holes

The ingoing Vaidya metric is introduced as a model for a non-rotating uncharged black hole emitting Hawking radiation. This metric is expected to capture the physics of the spacetime for radial coordinates up to a small multiple (>1) of the Schwarzschild radius. For larger radii, it will give an excellent approximation to the spacetime geometry in the case of astrophysical black holes (M≥M⊙), except at extremely large distances from the horizon (exceeding the cosmic particle horizon). In the classroom, the model may serve as a first exploration of non-stationary gravitational fields. Several interesting predictions are developed. First, particles dropped early enough before complete evaporation of the black hole cross its horizon as easily as with an eternal black hole. Second, the Schwarzschild radius takes on the properties of an apparent horizon, and the true event horizon of the black hole is inside of it, because light can escape from the shrinking apparent horizon. Third, a particle released from rest close enough to the apparent horizon is strongly repelled and may escape to infinity. An interpretation is given, demonstrating that such a particle would be able to compete, for a short time, in a race with a photon.

On some curvature properties of Vaidya–Bonner metric

The Vaidya–Bonner metric is a non-static generalization of Reissner–Nordström metric and this paper deals with the investigation of the curvature restricted geometric properties of such a metric. The scalar curvature vanishes and several pseudosymmetric-type curvature conditions are fulfilled by this metric. Also, it is a [Formula: see text]-quasi-Einstein, [Formula: see text] and generalized Roter type manifold. As a special case, the curvature properties of Reissner–Nordström metric are obtained. It is noted that Vaidya–Bonner metric admits several generalized geometric structures in comparison to Reissner–Nordström metric and Vaidya metric.

Quasinormal modes for dynamical black holes

Realistic black holes are usually dynamical, noticeable or sluggish. The Vaidya metric is a significant and tractable model for simulating a dynamical black hole. In this study, we consider scalar perturbations in a dynamical Vaidya black hole, and explore the quasinormal modes by employing the matrix method. We find the proper boundary conditions of the quasinormal modes from physical analysis in the background of a dynamical black hole for the first time. The results show that the eigenfrequencies become different at the apparent horizon and null infinity, because the physical interactions propagate with finite velocity in nature. Any variation of the hole does not affect the boundary condition at null infinity in a finite time. The quasinormal modes originated around the horizon would not immediately come down to, but slowly goes to the final state following the mass accretion process of the hole. The precision of the matrix method is quite compelling, which reveals more details of the eigenfrequencies of the quasinormal mode of perturbations in the Vaidya spacetime.

Gravitational collapse of anisotropic stars

We study the gravitational collapse of a spherically symmetric anisotropic relativistic star within Einstein theory of gravity making use of one of our recently developed collapsing stellar models [{\it Astrophys. Space Sci.} {\bf361} 99 (2016)]. The final state of continual gravitational collapse of a massive star under regular initial conditions is analyzed in terms of the formation of black holes. To study the evolution of an anisotropic star undergoing gravitational collapse, it is assumed that the dissipation process happens in the form of radial heat-flux. The interior space-time is described by static metric matched at the boundary with Vaidya metric that describes the exterior to the radiating star. The initial static configuration is described by the relativistic solution obtained by Paul and Deb [{\it Astrophys. Space Sci.} {\bf354} 421 (2014)]. The impact of anisotropy on the dynamical gravitational collapse of a massive star is studied. The relativistic causal heat transport equation of the Maxwell-Cattaneo equation is utilized to show the dependence of anisotropy on the temperature profile of the collapsing system.

Kerr–Vaidya black holes

Kerr-Vaidya metrics are the simplest nonstationary extensions of the Kerr metric. We explore their properties and compare them with the near-horizon limits of the spherically symmetric self-consistent solutions (the ingoing Vaidya metric with decreasing mass and the outgoing Vaidya metric with increasing mass) for the evaporating and accreting physical black holes. The Newman-Janis transformation relates the corresponding Vaidya and Kerr-Vaidya metrics. For nonzero angular momentum, the energy-momentum tensor violates the null energy condition (NEC). However, we show that its structure differs from the standard form of the NEC-violating tensors. The apparent horizon in the outgoing Kerr-Vaidya metric coincides with that of the Kerr black hole. For the ingoing metric, its location is different. We derive the ordinary differential equation for this surface and locate it numerically. A spherically symmetric accreting black hole leads to a firewall -- a divergent energy density, pressure, and flux as perceived by an infalling observer. We show that this is also true for the outgoing Kerr-Vaidya metric

Out of equilibrium chiral vortical effect in holography

We study the chiral vortical effect far from equilibrium in a strongly coupled holographic field theory. Rotation is represented as a perturbation via a gravito-magnetic field on top of a five-dimensional charged AdS Vaidya metric. We also introduce a momentum relaxation mechanism by linear scalar field backgrounds and study the CVE dynamics as function of the charges, temperature and momentum relaxation. The far from equilibrium behavior shows that the CVE builds up with a significant delay in time compared to the quasi instantaneous equilibration of the background metric. We also pay special attention to the effects of the gravitational contribution to the axial anomaly in the CVE of the axial current. We develop an analytic estimate of this delay and also compute the quasi-normal modes near equilibrium which determine the late time ring down.

Gravitational collapse for the K-essence emergent Vaidya spacetime

In this paper, we study the gravitational collapse in the k-essence emergent gravity using a generalized Vaidya-type metric as a background. We also analyze the cosmic censorship hypothesis for this system. We show that the emergent gravity metric resembles closely to the new type of the generalized Vaidya metrics for null fluid collapse with the k-essence emergent mass function, where we consider the k-essence scalar field being a function solely of the advanced or the retarded time. This new type of k-essence emergent Vaidya metric has satisfied the required energy conditions. The existence of the locally naked central singularity, the strength and the strongness of the singularities for the k-essence emergent Vaidya metric are the interesting outcomes of the present work.

Embedding with Vaidya geometry

The Vaidya metric is important in describing the exterior spacetime of a radiating star and for describing astrophysical processes. In this paper we study embedding properties of the generalized Vaidya metric. We had obtained embedding conditions, for embedding into 5-dimensional Euclidean space, by two different methods and solved them in general. As a result we found the form of the mass function which generates a subclass of the generalized Vaidya metric. Our result is purely geometrical and may be applied to any theory of gravity. When we apply Einstein’s equations we find that the embedding generates an equation of state relating the null string density to the null string pressure. The energy conditions lead to particular metrics including the anti/de Sitter spacetimes.

Radiating-collapsing models satisfying Karmarkar condition

This paper presents a class of exact spherical symmetric solutions of the Einstein equations admitting heat-conducting anisotropic fluid as a collapsing matter. The exterior spacetime is assumed to be the Vaidya metric. This class of solutions is shown to satisfy all the energy conditions throughout the interior of the star, and the luminosity is time independent, radiating uniformly throughout the collapse.

K -essence emergent spacetime as a generalized Vaidya geometry

We establish a formal connection between the {\bf K}-essence emergent gravity scenario and generalizations of Vaidya spacetime. Choosing the {\bf K}-essence action to be of the Dirac-Born-Infeld variety, the physical spacetime to be a general static spherically symmetric black hole and restricting the {\bf K}-essence scalar field to be a function solely of the advanced or the retarded time, we show that the emergent gravity metric resembles closely the generalized Vaidya metrics for null fluid collapse proposed by Husain. Imposing null energy conditions on the emergent energy-momentum tensor derived from the emergent Einstein equation, restrictions are obtained on the functions characterizing the emergent metric for consistent identification with generalized Vaidya spacetimes. We discuss the possibility of dynamical horizons in the {\bf K-}essence emergent Vaidya spacetime. Admissible explicit black hole background metrics are discussed as examples.

P. C. Vaidya’s Contributions to Mathematics and Physics

Prahalad Chunnilal Vaidya was an eminent general relativist, gravitation theorist, physicist, mathematician, educationist and a follower of Gandhian philosophy in post-independence India. Apart from his scientific career, Vaidya is renowned for his Vaidya metric. Though he has contributed significantly to the scientific community, very few people are aware about him or his contributions. As 23 May 2019 was the 101st birth anniversary of Vaidya, here we present his contributions and their impact through a bibliometric study. This study presents an analysis of published research works of Vaidya. During his active career, he had contributed 102 publications, including 90 journal articles, 5 conference papers, 4 book chapters, 2 review articles and 1 report. His publications have received 2004 citations, h-index of 18 and i10-index of 29 from 1979 to 2018. We analysed Vaidya’s publications by type, country, journals, publishers, citations, year-wise growth, collaborated authors, top cited papers, etc. This bibliometric study is an effort to draw the attention of the younger generation of scientists to Vaidya and his contributions.

P.C. Vaidya, A Gandhian Mathematician-Physicist and Proponent of ‘Vaidya Metric’: Nearly in Oblivion

P.C. Vaidya, A Gandhian Mathematician-Physicist and Proponent of ‘Vaidya Metric’: Nearly in Oblivion

Vaidya spacetime in Brans\u2013Dicke gravity\u2019s rainbow

In this note we study an energy dependent deformation of a time dependent geometry in the background of Brans–Dicke gravity theory. The study is performed using the gravity’s rainbow formalism. We compute the field equations in Brans–Dicke gravity’s rainbow using Vaidya metric which is a time dependent geometry. We study a star collapsing under such conditions. Our prime objective is to determine the nature of singularity formed as a result of gravitational collapse and its strength. The idea is to test the validity of the cosmic censorship hypothesis for our model. We have also studied the effect of such a deformation on the thermalization process. In this regard we have calculated the important thermodynamical quantities such as thermalization temperature, Helmholtz free energy, specific heat and analyzed the behavior of such quantities.

Source with Nonzero Radial Pressure for the Vaidya Metric

A null fluid with radial “pressure” is proposed as a source generating Vaidya spacetime. The fluid is anisotropic with no transversal pressures and p = ρ/3 as its equation of state, where p is the isotropic pressure and ρ is the energy density. The radial energy flux is directed inward when \(\dot{m} > 0\) and the total energy flow crossing a surface of constant r resembles the Brown–York quasilocal energy (QLE). A modified Vaidya metric removes the singularity at the origin, and the corresponding QLE is investigated in terms of both r and the mass m(v) of the object.

Gravitational properties of light: The emission of counter-propagating laser pulses from an atom

The gravitational field of a laser pulse, although not detectable at the moment, comes with a peculiar feature which continues to attract attention; cause and effect propagate with the same speed, that of light. A particular result of this feature is that the gravitational field of an emitted laser pulse and the gravitational effect of the emitter's energy-momentum change are intimately entangled. In this article, a specific example of an emission process is considered - an atom, modeled as a point mass, emits two counter-propagating pulses. The corresponding curvature and the effect on massive and massless test particles is discussed. A comparison is made with the metric corresponding to a spherically symmetric massive object that isotropically emits radiation - the Vaidya metric.

Wave equations on the linear mass Vaidya metric

We discuss the near singularity region of the linear mass Vaidya metric. In particular we investi- gate the structure in the numerical solutions for the scattering of scalar and electromagnetic metric perturbations from the singularity. In addition to directly integrating the full wave-equation, we use the symmetry of the metric to reduce the problem to that of an ODE. We observe that, around the total evaporation point, quasi-normal like oscillations appear, indicating that this may be an interesting model for the description of the end-point of black hole evaporation.

On maximal analytical extension of the Vaidya metric

The classical Vaidya metric is transformed to the special diagonal coordinates in the case of the linear mass function allowing rather easy treatment. We find the exact analytical expressions for metric functions in these diagonal coordinates. Using these coordinates, we elaborate the maximum analytic extension of the Vaidya metric with a linear growth of the black hole mass and construct the corresponding Carter–Penrose diagrams for different specific cases. The derived global geometry is also seemingly valid for a more general behavior of the black hole mass in the Vaidya metric.