Search arXiv⌕ Search

arXiv · gr-qc/9706026

Generating New Perfect-fluid Solutions From Known Ones II

Abstract

The properties of a transformation previously considered for generating new perfect-fluid solutions from known ones are further investigated. It is assumed that the four-velocity of the fluid is parallel to the stationary Killing field, and also that the norm and the twist potential of the stationary Killing field are functionally related. This case is complementary to the case studied in our previous paper. The transformation can be applied to generate possibly new perfect-fluid solutions from known ones only for the case of barotropic equation of state rho+3p=0 or, alternatively, for the case of a static spacetime. For static spacetimes our method recovers the Buchdahl transformation. It is demonstrated, moreover, that Herlt's technique for constructing stationary perfect-fluid solutions from static ones is, actually, a special case of the method considered in the present paper.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Istvan Racz, Jozsef Zsigrai. 1997-06-10. Generating New Perfect-fluid Solutions From Known Ones II. https://doi.org/10.1088/0264-9381%2F14%2F7%2F031

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

Novel thermodynamic inequality for rotating AdS black holes

We propose a new thermodynamic inequality for stationary, asymptotically Anti-de Sitter rotating black holes, expressed in terms of their angular momentum, mass and thermodynamic volume as $ 4πJ^2/(3MV)<1 $. For the solutions considered, this inequality follows from the requirement that the thermodynamic identities admit a physical horizon with positive area. We examine Kerr(-Newman)-AdS, Kerr-Sen-AdS, pairwise-equal four-charge AdS black holes, charged rotating AdS black strings, and charged rotating AdS C-metrics, finding strong supporting evidence for the inequality across different horizon topologies. We then reformulate the inequality in terms of the underlying metric parameters and compare the resulting constraints with the corresponding regularity and horizon-existence conditions. This analysis shows that the proposed inequality has different physical content for different geometries. We further examine charged super-entropic black holes, for which the ultraspinning limit leads instead to a lower bound on the thermodynamic ratio. This result is consistent with the violation of the reverse isoperimetric inequality characteristic of super-entropic solutions. Moreover, when combined with the refined reverse isoperimetric inequality, the proposed bound ensures the physicality of the Kerr-AdS reference solution entering the refined bound and thereby yields the conventional reverse isoperimetric inequality. We also extend the proposed relation to higher dimensions and test it for singly spinning thin AdS black ring with nonspherical horizon topology, finding that the corresponding inequalities are satisfied throughout the thin-ring regime.

gr-qc↗

Varying Newton constant, entropy and the black hole evaporation law

We assume that the Newton potential of a spherically symmetric body of mass $M$ is $V=-G(M)Mr^{-1}$, where the Newton constant $G$ may depend on $M$. We insert this assumption in the Schwarzschild solution. We discuss varying $G$ in the black hole thermodynamics and black hole evaporation law. We extend the Bekenstein-Hawking formula $\hbar GS=\frac{1}{4}A$, where $S$ is the entropy and $ A$ the area, to a varying $G$. It is shown that if $G(M)$ is of the form of a power-law $G\simeq M^{-Γ}$ then $G(M)S\simeq A$ is still preserved but the evaporation law substantially depends on the function $G(M)$.

gr-qc↗

Relativistic mode sums for neutron-star tidal response

Time-dependent tidal interactions during the late inspiral of binary neutron stars encode valuable information about neutron-star structure, but systematically extending the familiar Newtonian mode-sum picture into full general relativity is nontrivial. In this paper, we develop a practical relativistic implementation of mode-sum tidal response for non-rotating neutron stars in Regge-Wheeler gauge. Using near-zone boundary conditions, we systematically define the interior tidal field, the relativistic overlap integrals, and the corresponding mode amplitudes. The good is that the dominant f-mode contribution is remarkably robust, reproducing the direct matching calculation to within $\sim 3$\% across the equations of state we consider. The bad is that the operator governing mode inner product is not positive definite on the full Regge-Wheeler-gauge function space, so the relativistic mode sum truncated at ${\cal{O}}(ω^2)$ is not expected to strictly converge to the direct matching solution. The subtle is that the tidal field inside the star is not unique, although this ambiguity has only a limited impact on the dominant f-mode response for the classes of extensions studied here. Our results establish the practical utility of relativistic mode-sum approximations, while making clear that their predictive power comes from a controlled low-mode description, rather than from a formally convergent strong-field expansion.

gr-qc↗