Semiclassical relativistic stars
Abstract
We present strong evidence that semiclassical gravity can give place to selfconsistent ultracompact stars beyond the Buchdahl limit. We integrate the semiclassical equations of (spherically symmetric) stellar equilibrium for a constantdensity 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 StressEnergy 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.
 Publication:

Scientific Reports
 Pub Date:
 September 2022
 DOI:
 10.1038/s41598022198368
 arXiv:
 arXiv:2110.15808
 Bibcode:
 2022NatSR..1215958A
 Keywords:

 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 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