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Gravastar formation: What can be the evidence of a black hole?

Ken-ichi Nakao, Chul-Moon Yoo, and Tomohiro Harada
Phys. Rev. D 99, 044027 – Published 15 February 2019

Abstract

Any observer outside black holes cannot detect any physical signal produced by the black holes themselves, since, by definition, the black holes are not located in the causal past of the outside observer. In fact, what we regard as black hole candidates in our view are not black holes but will be gravitationally contracting objects. As well known, a black hole will form by a gravitationally collapsing object in the infinite future in the views of distant observers like us. At the very late stage of the gravitational collapse, the gravitationally contracting object behaves as a blackbody due to its gravity. Due to this behavior, the physical signals produced around it (e.g., the quasinormal ringings and the shadow image) will be very similar to those caused in the eternal black hole spacetime. However, those physical signals do not necessarily imply the formation of a black hole in the future, since we cannot rule out the possibility that the formation of the black hole is prevented by some unexpected event in the future yet unobserved. As such an example, we propose a scenario in which the final state of the gravitationally contracting spherical thin shell is a gravastar that has been proposed as a final configuration alternative to a black hole by Mazur and Mottola. This scenario implies that time necessary to observe the moment of the gravastar formation can be much longer than the lifetime of the present civilization, although such a scenario seems to be possible only if the dominant energy condition is largely violated.

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  • Received 2 November 2018

DOI:https://doi.org/10.1103/PhysRevD.99.044027

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Ken-ichi Nakao1, Chul-Moon Yoo2, and Tomohiro Harada3

  • 1Department of Mathematics and Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan
  • 2Gravity and Particle Cosmology Group, Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
  • 3Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan

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Issue

Vol. 99, Iss. 4 — 15 February 2019

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