Universal interferometric signatures of a black hole's photon ring
Abstract
The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin "photon ring," which is composed of an infinite sequence of selfsimilar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole "shadow," becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high order subrings. Here, we show that these subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.
 Publication:

Science Advances
 Pub Date:
 March 2020
 DOI:
 10.1126/sciadv.aaz1310
 arXiv:
 arXiv:1907.04329
 Bibcode:
 2020SciA....6.1310J
 Keywords:

 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 11 pages, 8 figures. Published in Science Advances