Lower bound on the compactness of isotropic ultra-compact objects

Shahar Hod

doi:10.1103/physrevd.97.084018

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arXiv · 1810.03618

Lower bound on the compactness of isotropic ultra-compact objects

Shahar Hod

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Abstract

Horizonless spacetimes describing spatially regular ultra-compact objects which, like black-hole spacetimes, possess closed null circular geodesics (light rings) have recently attracted much attention from physicists and mathematicians. In the present paper we raise the following physically intriguing question: How compact is an ultra-compact object? Using analytical techniques, we prove that ultra-compact isotropic matter configurations with light rings are characterized by the dimensionless lower bound $\text{max}_r\{2m(r)/r\}>7/12$ on their global compactness parameter.

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Shahar Hod. 2018-10-08. Lower bound on the compactness of isotropic ultra-compact objects. https://doi.org/10.1103/physrevd.97.084018

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