General Relativity & Quantum Cosmology

Over the last 20 years, advances in high angular resolution imaging technology has enabled the motions of individual stars to be tracked at the Galactic Center. This has provided the best evidence to date not only for the presence of a supermassive black hole at the center of our Galaxy, but for the existence of black holes in general. These high resolution measurements have also revealed an environment surrounding the black hole that is quite unexpected in a number of ways, challenging our understanding of the physical processes between black holes and their surround stars and gas. As the only galactic nucleus in which individual stellar orbits can be measured, the Galactic Center is now offering new insights into the fundamental physics of black holes, with unique tests of Einstein's theory of General Relativity on the horizon, and the astrophysics processes between black holes and their host galaxies that are thought to shape the co-evolution of central black holes and their host galaxies. I will review the work done by the UCLA Galactic Center Group and others on measuring stellar orbits, with an emphasis on (1) our recent model for G2 as a binary star that has been driven to merge through three-body interactions with the central black hole, (2) precision measurements of the distance to the black hole (R0), which is a fundamental constant for many astrophysical studies (e.g., galactic structure), and the mass of the black hole (Mbh), which as a ratio with R0 (Mbh/R0) is a key ingredient for interpreting future EHT measurements of the black hole's shadow, and (3) upcoming tests of General Relativity that are within reach through precision measurements of stellar orbits.

We discuss how polarized emission can place constraints on the properties of accretion flows and jets in the strong gravity regime for systems like SgrA* and M87 being observed by the Event Horizon Telescope.

Black holes are the engines that power quasars and active galactic nuclei throughout cosmic time. The masses of black holes in nearby galaxies define clear correlations with the properties of their host galaxies. These results suggest that black holes, while a thousand times lighter than the galaxy, grow alongside their hosts during its cosmic evolution. I will discuss the growth of black holes, and the establishment of the connection between galaxies and black holes.