Imaging Black Holes with the Event Horizon Telescope
Geoffrey C. Bower (ASIAA, UH Manoa)
for the Event Horizon Telescope Collaboration

The Event Horizon Telescope (EHT) is a global submillimeter-wavelength very long baseline array that produces the highest angular resolution images of black holes.  In 2019, the EHT announced an image of the supermassive black hole in the elliptical galaxy M87 that showed ring-like emission as the result of strong gravitational light-bending and photon capture at the event horizon.   The observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity.   We derive a black hole mass of M=(6.5 +/- 0.7) x 10^9 M_Sun.  Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.  The collaboration has also produced the first map of a black hole magnetosphere and constraints on the nature of black hole accretion and jet-launching.  I will also discuss the prospects for further EHT imaging, including the Galactic Center black hole, Sagittarius A*.  EHT images of Sgr A* provide a very important complement to the recent Nobel-Prize-winning work on stellar measurements of the Galactic Center black hole.