SETI bioastro: Ejection of Hyper-Velocity Stars from the Galactic Centre by Intermediate-Mass B

From: LARRY KLAES (ljk4_at_msn.com)
Date: Sun Jul 23 2006 - 00:00:17 PDT

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    Astrophysics, abstract
    astro-ph/0607455

    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.

    http://arxiv.org/abs/astro-ph/0607455


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