Astro Lunch Talks
Wednesdays, 11:45am-1:00pm, 76-1275 Carlson Learning Center.
Topics will be emailed prior to the talk. Please contact Ben Sargent for more information.
Upcoming Talk Details
Date/Time: May 20, 12:00pm 76-1275
Speaker: David Merritt
TITLE: Recent results on the final-parsec problem
ABSTRACT: A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence.
Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers suggest that this stalling may not occur. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the N-body simulations than in real galaxies. I will describe a novel Monte-Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. I show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. The binary hardening rate is always substantially lower than the maximum possible, "full-loss-cone'' rate, and it decreases with time, but stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale less than about one Gyr in any triaxial galaxy. I also discuss the evolution of the binary’s eccentricity.
2014-2015 Academic Year Scheduled Dates
|2013-2014 Academic Year Astro Lunch Talks|