From: LARRY KLAES (ljk4_at_msn.com)
Date: Sun Jul 23 2006 - 00:00:17 PDT
From: Holger Baumgardt [view email]
Date: Wed, 19 Jul 2006 21:09:32 GMT (124kb)
Ejection of Hyper-Velocity Stars from the Galactic Centre by
Intermediate-Mass Black Holes
Authors: Holger Baumgardt, Alessia Gualandris, Simon Portegies Zwart
Comments: 10 pages, 10 figures, MNRAS in press
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 considered IMBHs of different
masses, all starting from circular orbits at an initial distance of 0.1 pc.
We find that the IMBHs sink to the centre of the Galaxy due to dynamical
friction, 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. Since the HVS carry with them information about their origin, in
particular in the moment of ejection, the velocity distribution and the
direction in which they escape the Galaxy, detecting a population of HVS
will provide insight in the ejection processes and could therefore provide
indirect evidence for the existence of IMBHs.
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). HVS are ejected almost isotropically, which makes IMBH induced
ejections hard to distinguish from ejections due to encounters of stellar
binaries with a 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.
The velocity distribution of HVS generated by inspiralling IMBHs is also
nearly independent of the mass of the IMBH and can be quite distinct from
one generated by binary encounters.
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
profile, which takes at least 100 Myrs to replenish.
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