Princeton University Gravity Group Astrophysics|Cosmology Lunch

Fri, Dec 2, 2011, 12:00 pm to 1:30 pm
Joseph Henry Room
Title: Roche Accretion Of Stars Close To Massive Black Holes Speaker: Lixin (Jane) Dai Stanford University Abstract: We consider the Roche accretion in an Extreme Mass-Ratio Inspiral (EMRI) binary system formed by a star orbiting a massive black hole. The ultimate goal is to constrain the mass and spin of the black hole and confirm general relativity in the strong-field regime from the resulted quasi-periodic signals. Before accretion starts, the star orbits the hole in a circular, equatorial stellar orbit, which shrinks due to gravitational radiation. New fitting formulae are presented for the inspiral time and the radiation-reaction torque in the relativistic regime. If the inspiralling star fills its Roche lobe outside the Innermost Stable Circular Orbit (ISCO) of the hole, gas will flow through the inner Lagrange point (L1) to the hole. We give new relativistic interpolation formulae for the volume enclosed by the Roche lobe. If this mass-transfer happens on a time scale faster than the thermal time scale but slower than the dynamical time scale, the star will evolve adiabatically, and, in most cases, will recede from the hole filling its Roche lobe. We calculate how the stellar orbital period and mass-transfer rate will change through the “Roche evolution