------------------------------------------------------------------------
 HyperVelocityCollisions.tex MNRAS, September 2006
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%astro-ph/0609440

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\newcommand{\SgrA}{Sgr A$^*$}

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\title{Hypervelocity Collisions of Binary Stars at the Galactic Centre}

\author[Idan Ginsburg \& Abraham Loeb]{Idan Ginsburg\thanks{E-mail:
iginsburg@cfa.harvard.edu} \& Abraham
Loeb\thanks{E-mail:aloeb@cfa.harvard.edu}\\ Harvard-Smithsonian Center for
Astrophysics, 60 Garden St., MS 51, Cambridge, MA 02138, USA\\}


\begin{document}
\maketitle

\begin{abstract}

Recent surveys have identified seven hypervelocity stars (HVSs) in the
halo of the Milky Way.  Most of these stars may have originated from the
breakup of binary star systems by the nuclear black hole SgrA*.  In some
instances, the breakup of the binary may lead to a collision between its
member stars. We examine the dynamical properties of these collisions by
simulating thousands of different binary orbits around SgrA* with a direct
N-body integration code.  For some orbital parameters, the two stars
collide with an impact velocity lower than their escape velocity and may
therefore coalesce.  Some of the massive S-stars near Sgr A* might be the
merger remnants of binary systems.

\end{abstract}

\begin{keywords}
black hole physics-Galaxy:center-Galaxy:kinematics and dynamics-stellar
dynamics
\end{keywords}