Ejection of High-Velocity Stars from the Galactic Center by an Inspiraling Intermediate-Mass Black Hole
Abstract
The presence of young stars near Sgr A* remains unexplained. One idea for their origin posits that the stars were brought in by an intermediate-mass black hole (IMBH) that inspiraled into the Galactic center a few million years ago. Yu & Tremaine have argued that in this case some old stars in the Sgr A* cusp would be ejected by hard gravitational collisions with the IMBH. We derive a general expression for the phase-space distribution of the ejected high-velocity stars, given the distribution function of the stars in the cusp. We compute it explicitly for the Peebles-Young distribution function of the cusp and model the time-dependent ejection of stars during the IMBH inspiral. We find that (1) the stars are ejected in a burst lasting a few dynamical friction timescales; if Gaia detects the ejected stars, they are likely to be produced by a single inspiral event. (2) If the inspiral is circular, then in the beginning of the burst the velocity vectors of the ejected stars cluster around the inspiral plane but rapidly isotropize as the burst proceeds. (3) If the inspiral is eccentric, then the stars are ejected in a broad jet roughly perpendicular to the IMBH orbit's Runge-Lenz vector. In a typical cusp the orbit will precess with a period of ~105 yr, and the rate of ejection into our part of the Galaxy (as defined by Gaia visibility) will be modulated periodically. Gaia, together with ground-based follow-up observations, will be able to clock many high-velocity stars back to their ejection, thus measuring some of the above phenomena. This would provide a clear signature of the IMBH inspiral in the past 10-20 Myr.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2006
- DOI:
- 10.1086/507830
- arXiv:
- arXiv:astro-ph/0508193
- Bibcode:
- 2006ApJ...653.1203L
- Keywords:
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- Black Hole Physics;
- Galaxy: Center;
- Galaxy: Nucleus;
- Astrophysics
- E-Print:
- 12 pages, including 7 figures