Ejection of Hyper-Velocity Stars by Intermediate-Mass Black Holes

Abstract

We have performed N-body simulations of the formation of hyper-velocity stars (HVS) in the centre of the Milky Way due to inspiralling intermediate-mass black holes (IMBHs). We find that due to dynamical friction, IMBHs sink into the centre of the Galaxy where they deplete the central cusp of stars. Some of these stars become HVS and are ejected with velocities sufficiently high to escape the Galaxy.Our simulations show that HVS are generated in short bursts which last only a few Myrs until the IMBH is swallowed by the supermassive black hole (SMBH). After the HVS have reached the galactic halo, their escape velocities correlate with the distance from the Galactic centre in the sense that the fastest HVS can be found furthest away from the centre. Finally, our simulations show that the presence of an IMBH in the Galactic centre changes the stellar density distribution inside r < 0.02 pc into a core profle, which takes at least 100 Myrs to replenish.