2020 Watson Memorial Colloquium: "Imaging Black Holes With the Event Horizon Telescope"

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.  I will discuss the numerous results that the EHT Collaboration has produced since that first result and 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 Nobel-Prize-winning work on stellar characterization of the Galactic Center black hole.

Dr. Geoffrey Bower is Project Scientist for the Event Horizon Telescope Collaboration, Chief Scientist for Hawaii Operations with Academia Sinica Institute of Astronomy and Astrophysics, and Affiliate Graduate Faculty with UH Manoa Physics and Astronomy.  A graduate of Princeton University and UC Berkeley, he has also held research and teaching positions at UC Berkeley, the National Radio Astronomy Observatory, and the Max Planck Institute for Radioastronomy.  His interests are in black holes, neutron stars, the dynamic radio sky, and radio astronomy instrumentation.