The tidal disruption of stars by a massive black hole at the center of a galaxy.

Abstract

Studies of the luminosity evolution of optical Quasi-Stellar Objects (QSOs) suggest that a large number of normal-looking galaxies today have a central massive black hole. These galaxies once contained Active Galactic Nuclei (AGN), but a dwindling fuel supply forced the central engine to fade. If one of these galaxies happens to be close enough, it might be possible to detect the central black hole by the effects it has on the kinematics and surface density of stars in the galactic nucleus. But, for the majority of galaxies, it is not feasible to observe these effects due to their great distance. Not feasible, that is, until the black hole disrupts a passing star. The debris of the star will form an accretion disk around the black hole. The galactic nucleus will then become a reborn AGN. It is then possible to detect the black hole by the sudden appearance of a compact source of extreme UV and X-ray photons at the center of a galaxy. Broad, double-peaked emission lines may also appear, giving conclusive evidence that an accretion disk has formed around a massive black hole. A survey to detect flares from galactic nuclei resulting from tidally-disrupted stars could possibly answer whether or not most galaxies go through an AGN phase. In this work, we will use Smoothed Particle Hydrodynamics (SPH) simulations to remove much of the uncertainty that existed in previous work on the tidal disruption of stars. These works were forced to assume that stars which passed inside the Roche limit of a black hole were completely accreted by the black hole. We will replace this assumption with the results of our SPH simulations, and find that previous works overestimated the rate at which gas is stripped from stars by a factor of two. We will then review the observational consequences of a disruption event, and consider two cases in which such an event may have been witnessed.