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Black Hole Images as Tests of General Relativity: Effects of Plasma Physics

Özel, Feryal; Psaltis, Dimitrios; Younsi, Ziri; (2022) Black Hole Images as Tests of General Relativity: Effects of Plasma Physics. The Astrophysical Journal , 941 (1) , Article 88. 10.3847/1538-4357/ac9fcb. Green open access

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Abstract

The horizon-scale images of black holes obtained with the Event Horizon Telescope have provided new probes of their metrics and tests of general relativity. The images are characterized by a bright, near-circular ring from the gravitationally lensed emission from the hot plasma and a deep central depression cast by the black hole. The metric tests rely on the fact that the bright ring closely traces the boundary of the black hole shadow with a small displacement that has been quantified using simulations. In this paper we develop a self-consistent covariant analytic model of the accretion flow that spans a broad range of plasma conditions and black hole properties to explore the general validity of this result. We show that, for any physical model of the accretion flow, the ring always encompasses the outline of the shadow and is not displaced by it by more than half the ring width. This result is a consequence of conservation laws and basic thermodynamic considerations and does not depend on the microphysics of the plasma or the details of the numerical simulations. We also present a quantitative measurement of the bias between the bright ring and the shadow radius based on the analytical models.

Type: Article
Title: Black Hole Images as Tests of General Relativity: Effects of Plasma Physics
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/1538-4357/ac9fcb
Publisher version: https://doi.org/10.3847/1538-4357/ac9fcb
Language: English
Additional information: Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery-pp.ucl.ac.uk/id/eprint/10162341
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