Antonio Rodriguez (Caltech): "The Nearest Black Holes Are Quiet (But White Dwarfs Are Not)"

While the Milky Way is predicted to harbor around 100 million stellar-mass black holes (BHs), only about two dozen have been securely identified as such. The vast majority of such systems were identified through their powerful X-ray outbursts, which approach Eddington luminosities, but the newest two systems were identified through their gravitational influence on their companion stars using precise astrometry from Gaia. In this talk, I will show why we expected to see X-rays from at least one of these two newest BHs, and what the implications are of not having seen any X-rays from either system. In the second half of the talk, I will show successful X-ray detections \u2014 recent discoveries of accreting magnetic white dwarfs (WDs) in the X-ray. Magnetic WDs are interesting since the origin of their magnetism is uncertain, but has recently been proposed to be due to a dynamo mechanism similar to that of the Earth. I will conclude by showing that the near X-ray future is bright, with the deepest-ever all-sky X-ray survey SRG/eROSITA leading to the discovery of a wealth of new accreting compact objects.