Kerr-de Sitter Universe

TL;DR

This paper analyzes the horizon structure, extremal conditions, and conformal geometry of Kerr-de Sitter black holes, emphasizing the effects of the cosmological constant on their properties and spacetime embedding.

Contribution

It provides explicit numerical results for Kerr-de Sitter black hole spins, explores their horizon structure dependence on b3, and examines the conformal and spatial geometry of the extended spacetime.

Findings

Maximal spin values depend on b3 and are numerically characterized.

Spatial sections are 3-spheres with horizons as spherical sections at the poles.

The causal structure varies with the definition of constant-time slices, showing black or white hole configurations.

Abstract

It is now widely accepted that the universe as we understand it is accelerating in expansion and fits the de Sitter model rather well. As such, a realistic assumption of black holes must place them on a de Sitter background and not Minkowski as is typically done in General Relativity. The most astrophysically relevant black hole is the uncharged, rotating Kerr solution, a member of the more general Kerr-Newman metrics. A generalization of the rotating Kerr black hole to a solution of the Einstein's equation with a cosmological constant $\Lambda$ was discovered by Carter \cite{DWDW}. It is typically referred to as the Kerr-de Sitter spacetime. Here, we discuss the horizon structure of this spacetime and its dependence on $\Lambda$. We recall that in a $\La>0$ universe, the term `extremal black hole' refers to a black hole with angular momentum $J > M^2 $. We obtain explicit numerical results for the black hole's maximal spin value and get a distribution of admissible Kerr holes in the ($\Lambda$, spin) parameter space. We look at the conformal structure of the extended spacetime and the embedding of the 3-geometry of the spatial hypersurfaces. In analogy with Reissner-Nordstr\"{o}m -de Sitter spacetime, in particular by considering the Kerr-de Sitter causal structure as a distortion of the Reissner-Nordstr\"{o}m-de Sitter one, we show that spatial sections of the extended spacetime are 3-spheres containing 2-dimensional topologically spherical sections of the horizons of Kerr holes at the poles. Depending on how a $t=$ constant 3-space is defined these holes may be seen as black or white holes (four possible combinations).