Titel:

Creation of hypervelocity stars in the galactic centre by inspiraling intermediate-mass black holes

Oral invited talk

Abstract:

In the late 1980s Hills predicted that runaway stars could be accelerated to high velocities by dynamical encounters with the supermassive black hole (SMBH) in the galactic centre and the recently discovered hyper-velocity stars in the galactic halo could be the first examples for such objects.

At present two mechanisms are considered capable of creating hyper-velocity
stars: Encounters of stellar binaries with an SMBH and the acceleration of single stars by an intermediate-mass black holes (IMBHs) orbiting the SMBH. In order to test which scenario is operating in our galaxy, we have
performed a series of $N$-body simulations modeling the encounter of single stars with an IMBH. Our runs consisted of stars distributed in a stellar cusp around a central SMBH of $3\cdot 106 M_\odot$ and IMBHs of varying mass and our main aim was to test if IMBH ejection leads to predictions which can be tested once enough hyper-velocity stars have been found.

We found that IMBHs sink towards the SMBH due to dynamical friction and
typically eject HVS for a timespan of few Myrs between the time an IMBH reaches the galactic centre and the time it merges with the SMBH. The
escape time and spatial distribution of also HVS hold important information
about their origin and will allow to test their origin once enough HVS
have been found.