# Orbital inspiral into a massive black hole in a galactic center

## Tal Alexander and Clovis Hopman

(1) Faculty of Physics, The Weizmann Institute of Science, POB 26, Rehovot 76100, Israel

### Paper: 2003, ApJL, 590, L29

**Abstract:**
A massive black hole (MBH) in a galactic center drives a flow of stars
into nearly radial orbits to replace those it destroyed. Stars whose
orbits cross the event horizon r_{s} or the tidal disruption radius r_{t}
are promptly destroyed in an orbital period P. Stars with orbital
periapse r_{p} slightly larger than the sink radius q=max(r_{s},r_{t}) may
slowly spiral in due to dissipative interactions with the MBH,
e.g. gravitational wave emission, tidal heating or accretion disk
drag, with observable consequences and implications for the MBH growth
rate. Unlike prompt destruction, the inspiral time is typically >>P.
This time is limited by the same scattering process that initially
deflected the star into its eccentric orbit, since it can deflect it
again to a wider orbit where dissipation is inefficient. The ratio
between slow and prompt event rates is therefore much smaller than
that implied by the ratio of cross-sections, r_{p}/q, and so only
prompt disruption contributes significantly to the mass of the
MBH. Conversely, most stars that scatter off the MBH survive the
extreme tidal interaction ("tidal scattering"). We derive general
expressions for the inspiral event rate and the mean number of
inspiraling stars, and show that the survival probability of tidally
scattered stars is 1, and that the number of tidally heated stars
("squeezars") and gravity wave emitting stars in the Galactic Center
is 0.1-1.

Preprints available from the authors at tal.alexander@weizmann.ac.il
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