Stellar Tidal Processes Near Massive Black Holes

Abstract

Close tidal interactions of stars with a central massive black hole (MBH) or with other stars in the high density cusp around it can affect a significant fraction of the stellar population within the MBH radius of influence. We consider three strong processes that have the potential of modifying stellar structure and evolution there. (1) Tidal spin-up by hyperbolic star-star encounters. (2) Tidal scattering of stars on the MBH. (3) Tidal heating of inspiraling stars - "squeezars" - that were tidally captured by the MBH. We discuss the implications for stellar populations near MBHs and for the growth of MBHs by tidal disruption of stars, and the possible observational signature of such processes near the MBH in the Galactic Center. We compare the event rates of prompt tidal encounters (tidal disruption and tidal scattering) and slow inspiral events (squeezars / tidal capture), and find that tidal capture is at least an order of magnitude less efficient than prompt disruption. This means that past studies, which assigned similar weights to prompt disruption and tidal capture, over-estimated the contribution of tidal disruption to the growth of the MBH by at least a factor of two.