Semiclassical relativistic stars

Abstract

We present strong evidence that semiclassical gravity can give place to self-consistent ultracompact stars beyond the Buchdahl limit. We integrate the semiclassical equations of (spherically symmetric) stellar equilibrium for a constant-density classical fluid. The semiclassical contribution is modelled by a quantum massless scalar field in the only static vacuum state compatible with asymptotic flatness (Boulware vacuum). The Renormalized Stress-Energy Tensor (RSET) is firstly approximated by the analytic Polyakov approximation. This already reveals a crucial difference with respect to purely classical solutions: stars with compactness close to that of a black hole exhibit bounded pressures and curvatures up to a very small central core compared with the star radius. This suggests that a more refined approximation to the RSET at the core may give rise to strictly regular configurations. Following this suggestion, we prove that a minimal deformation of the Polyakov approximation inside the central core is sufficient to produce regular ultracompact stellar configurations.

17 pages, 5 figures. Expanded main text significantly with extra details and explanations. Added a new Figure (Fig. 4), Figs. 2 and 3 replaced. Version to appear in Scientific Reports Gravitational Waves guest edited collection

References in corpus (4)

• Tests for the existence of horizons through gravitational wave echoes
• How does a dark compact object ringdown?
• The lifetime problem of evaporating black holes: mutiny or resignation
• Semiclassical constant-density spheres in a regularized Polyakov approximation

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• Boulware Vacuum vs. Regularity: Thoughts on Anomaly-Induced Effective Action
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• Stellar equilibrium on a physical vacuum soil
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• Trace anomaly contributions to semi-classical wormhole geometries
• Imprints of quantum vacuum fluctuations on the gravitational field of a spherical mass
• Macroscopic backreaction of the trace anomaly on classical vacuum backgrounds