Physics/Astronomy Colloquium

Experimental Studies of Black Holes: Status & Prospects

More than a century ago, Albert Einstein presented his general theory of gravitation. One of the predictions of this theory is that not only particles and objects with mass, but also the quanta of light, photons, are tied to the curvature of space-time, and thus to gravity. There must be a critical mass density, above which photons cannot escape. These are black holes. It took fifty years before possible candidate objects were identified by observational astronomy. Another fifty years have passed, until we finally can present detailed and credible experimental evidence that black holes of 10 to 10¹⁰ times the mass of the Sun exist in the Universe. Three very different experimental techniques have enabled these critical experimental breakthroughs. It has become possible to investigate the space-time structure in the vicinity of the event horizons of black holes. I will summarize these interferometric techniques, and discuss the spectacular recent improvements achieved with all three techniques. In conclusion, I will sketch where the path of exploration and inquiry may lead to in the next decades.

Reinhard Genzel, born 1952 in Bad Homburg v. d. H., Germany, is one of the Directors of Max Planck Institute for Extraterrestrial Physics, Professor in the Graduate School of the University of California, Berkeley and an Honorary Professor at the Ludwig Maximilian University, Munich. He is a Scientific Member of the Max Planck Society and a member of the US National Academy of Sciences. His research interests include astrophysics of galactic nuclei, star formation, kinematics and cosmic evolution of galaxies, massive black holes and experimental infrared, submillimeter and millimeter astronomy. He has received numerous honours and awards, including the Shaw Prize of The Shaw Prize Foundation and the Crafoord Prize in Astronomy. In 2020, he received the Nobel Prize in Physics, jointly with Andrea Ghez, for the discovery of a supermassive compact object at the centre of our galaxy.