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arXiv · 2102.07784

The light ring and the appearance of matter accreted by black holes

Vitor Cardoso·Francisco Duque·Arianna Foschi
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Abstract

The geometry of black hole spacetimes can be probed with exquisite precision in the gravitational-wave window, and possibly also in the optical regime. We study the accretion of bright spots -- objects which emit strongly in the optical or in gravitational waves -- by non-spinning black holes. The emission as the object falls down the hole is dominated by photons or gravitons orbiting the light ring, causing the total luminosity to decrease exponentially as ${\cal L}_o\sim e^{-t/(3\sqrt{3}\,M)}$. Late-time radiation is blueshifted, due to its having been emitted during the infall, trapped at the light ring and subsequently re-emitted. These universal properties are a clear signature of the existence of light rings in the spacetime, and not particularly sensitive to near horizon details.

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Vitor Cardoso, Francisco Duque, Arianna Foschi. 2021-02-15. The light ring and the appearance of matter accreted by black holes. https://doi.org/10.1103/physrevd.103.104044

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