Degenerate Stars and Gravitational Collapse in AdS/CFT

TL;DR

This paper models degenerate stars in AdS space using holography, deriving their properties and collapse conditions, and relates these to phase transitions in the dual boundary theory.

Contribution

It constructs composite CFT operators for fermionic states, analyzes their gravitational stability, and identifies a Chandrasekhar limit for collapse in the holographic context.

Findings

Degenerate stars match boundary calculations in mass and radius.

A Chandrasekhar limit is derived for gravitational collapse.

Collapse corresponds to a phase transition in the boundary theory.

Abstract

We construct composite CFT operators from a large number of fermionic primary fields corresponding to states that are holographically dual to a zero temperature Fermi gas in AdS space. We identify a large N regime in which the fermions behave as free particles. In the hydrodynamic limit the Fermi gas forms a degenerate star with a radius determined by the Fermi level, and a mass and angular momentum that exactly matches the boundary calculations. Next we consider an interacting regime, and calculate the effect of the gravitational back-reaction on the radius and the mass of the star using the Tolman-Oppenheimer-Volkoff equations. Ignoring other interactions, we determine the "Chandrasekhar limit" beyond which the degenerate star (presumably) undergoes gravitational collapse towards a black hole. This is interpreted on the boundary as a high density phase transition from a cold baryonic phase to a hot deconfined phase.