Electromagnetic Flares from the Tidal Disruption of Stars by Massive Black Holes
November 08, 2010
Abstract: A star that wanders too close to a massive black hole (BH) gets shredded by the BH’s tidal gravity. Stellar gas soon falls back to the BH at a rate initially exceeding the Eddington rate, releasing a flare of energy as gas accretes. How often this process occurs is uncertain at present, as is the physics of super-Eddington accretion (which is relevant for BH growth and feedback at high redshift as well). Excitingly, transient surveys like the Palomar Transient Factory (PTF), Pan-STARRS and LSST should shed light on these questions soon — in anticipation, I predict photometric and spectroscopic properties of tidal flares. Early on, much of the falling-back gas should blow away in a wind, producing luminous optical emission imprinted with blueshifted UV absorption lines. If the shock at pericenter is unable to thermalize, photons should Compton upscatter to produce hard X-ray emission, erasing the UV lines but providing X-ray absorption lines. I will describe predicted detection rates for PTF, Pan-STARRS and LSST, and discuss the substantial challenge of disentangling these events from supernovae. These surveys should significantly improve our knowledge of stellar dynamics in galactic nuclei, the physics of super-Eddington accretion, the demography of IMBHs, and the role of tidal disruption in the growth of massive BHs.