AlbaNova Colloquium

A tale of two black holes: Sgr A* and M87*

by Prof. Sera B Markoff (API/GRAPPA, University of Amsterdam)


Black holes are one of the most exotic consequences of Einstein’s General Relativity, yet they are also very common, ranging from stellar remnants up to beasts billions of times more massive than our sun.  Despite their reputation as cosmic vacuum cleaners, they actually drive extremely complicated astrophysical systems that can majorly influence their surroundings.   Via their powerful outflows in particular, black holes shape the way the Universe looks today...but not at all times.  Black holes undergo cycles of activity, so to understand their role over cosmological timescales we need to understand not only how they power such outflows from just outside their event horizons, but also what drives their cyclic behaviour.   Thanks to the Event Horizon Telescope (EHT) we have now directly imaged the event horizon region for two nearby supermassive black holes:  Sgr A* in our own Galactic center, and M87* in the Virgo cluster of galaxies.  After a brief review of the key results so far, I will put them into the context of our greater understanding of black hole activity, with emphasis on the gains made by combining EHT observations with those from other multi-wavelength facilities.  I will also discuss the near- and longterm outlook for the studies of black hole astrophysics and their cosmic impact.