High velocity stars from close interaction of a globular cluster and a super massive black hole

TL;DR

This paper investigates how close interactions between a globular cluster and a supermassive black hole can produce high velocity stars, explaining their presence in the galactic halo through N-body simulation results.

Contribution

It introduces a mechanism based on N-body simulations showing how energy transfer during cluster-black hole interactions accelerates stars to high velocities.

Findings

Stars can reach velocities sufficient to escape the galaxy.

Some stars are stripped and orbit the galactic center.

The mechanism explains observed high velocity stars in the halo.

Abstract

Observations show the presence, in the halo of our Galaxy, of stars moving at velocities so high to require an acceleration mechanism involving the presence of a massive central black hole. Thus, in the frame of a galaxy hosting a supermassive black hole ($10^8$ $M_{\odot}$) we investigated a mechanism for the production of high velocity stars, which was suggested by the results of N-body simulations of the close interaction between a massive, orbitally decayed, globular cluster and the super massive black hole. The high velocity acquired by some stars of the cluster comes from the transfer of gravitational binding energy into kinetic energy of the escaping star originally orbiting around the cluster. After the close interaction with the massive black hole, stars could reach a velocity sufficient to travel in the halo and even overcome the galactic gravitational well, while some of them are just stripped from the globular cluster and start orbiting on precessing loops around the galactic centre.