Tidal processes very near the black hole in the Galactic Center

Tal Alexander

Weizmann Institute of Science

E-mail contact: tal.alexander@weizmann.ac.il

See Alexander, T., & Kumar, P. 2001, ApJ, 549, 948; Alexander, T., & Livio, M. 2001, ApJ, 560, L143

Unique conditions of extreme stellar density, high velocity and strong tidal fields exist very near a massive black hole (MBH). Observations of stars near SgrA* thus open a window to a new, previously unobserved regime of stellar dynamics and evolution, which is closely linked to the open issues of MBH formation and growth. I will describe several tidal processes that have the potential of strongly affecting stellar structure and evolution, and discuss their possible observational signature in the Galactic Center. These processes include (1) Tidal spin-up by star-star encounters (Alexander & Kumar 2001), which affects all stars within a large volume around the MBH. Such encounters are very different from those in a globular cluster since the high orbital velocities suppress tidal binary formation; (2) Tidal scattering of stars on the black hole (Alexander & Livio 2001), which is a global response of the system to the presence of a mass sink in its center, and affects a large fraction of the stars within the MBH's volume of influence; (3) Tidally powered stars orbiting the MBH (Alexander & Morris 2002), which is the complementary process to tidal scattering, and could provide a direct, observationally accessible probe of the tidal disruption that contributes to the MBH growth, and of the effects of extreme tidal fields on stellar structure.