The Leonard E Parker Center for Gravitation, Cosmology and Astrophysics holds frequent seminars on a broad range of ongoing cosmology and gravitation research topics. Unless otherwise noted, seminars are on Friday afternoons at 1:00 PM in KIRC 2175; there is a gathering for a brown bag lunch at 12:30.

Constraining relativity and astrophysics with Galactic Center orbits: Calibrating a Fisher matrix analysis against Markov Chain Monte Carlo
Hong Qi,Research Assistant, UWM Dept. of Physics

Recent investigations have provided proof-of-principle calculations suggesting measurements of stellar or pulsar orbits near the Galactic Center could strongly constrain the properties of the Galactic Center black hole, local matter, and even the theory of gravity itself. As in previous studies, we use a Markov Chain Monte Carlo to quantify what properties of the Galactic Center environment that measurements constrain. In this work, however, we also develop a simple but powerful analytic model (Fisher matrix) to understand what correlations are well-constrained and why. Using both tools, we conclude that existing measurements cannot constrain the spin of the galactic center black hole. Extrapolating to the precision and cadence of future experiments, we anticipate that the black hole spin can be precisely measured, extending previously-observed stellar orbits. If in addition future measurements include discovery of a new, tighter stellar orbit, then future data could conceivably enable tests of strong field gravity, by directly measuring the black hole quadrupole moment.