Light rings and long-lived modes in quasi-black hole spacetimes
Abstract
It has been argued that ultracompact objects, which possess light rings but no horizons, may be unstable against gravitational perturbations. To test this conjecture, we revisit the quasi-black hole solutions, a family of horizonless spacetimes whose limit is the extremal Reissner-Nordstr\"om black hole. We find a critical parameter at which the light rings just appear. We then calculate the quasinormal modes of the quasi-black holes. Both the WKB result and the numerical result show that long-live modes survive for the range where light rings exist, indicating that horizonless spacetimes with light rings are unstable. Our work provides a strong and explicit example that light rings could be direct observational evidence for black holes.
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Cite
@article{arxiv.2108.08967,
title = {Light rings and long-lived modes in quasi-black hole spacetimes},
author = {Minyong Guo and Zhen Zhong and Jinguang Wang and Sijie Gao},
journal= {arXiv preprint arXiv:2108.08967},
year = {2022}
}
Comments
matched version in prd