Institute of Astronomy

The Life of a Black-hole Binary

SpeakerTalk DateTalk Series
Sverre Aarseth25 July 2016Binary Stars Talks


The question of how a black hole binary interacts with the members of a star cluster has been addressed by N-body simulations. We concentrate on studying a single stellar-mass primordial black hole binary in a system of 50,000 or 100,000 stars subject to synthetic stellar evolution treated by the Cambridge STARS code. As expected, such a binary shrinks by imparting kinetic energy to field stars by the sling-shot mechanism. Since only a modest shrinkage is possible in practice, the onset of any relativistic effects requires a rather high eccentricity. This type of evolution appears to be characteristic of all the present models, thereby achieving a predicted maximum eccentricity exceeding 0.999 with many large actual values triggering post-Newtonian treatment. These sporadic events are induced by the Kozai-Lidov mechanism which is activated when a long-lived hierarchy is formed with high inclination. Alternatively, strong interactions may lead to the ejection of the massive black hole binary by recoil, in some cases with sufficient eccentricity for GR coalescence on a galactic time-scale. An observational feature of the binary evolution is that high-velocity escapers (> 100 km/s) are produced.