1999MNRAS.308..257B -
Mon. Not. R. Astron. Soc., 308, 257-270 (1999/September-1)
Red giant collisions in the Galactic Centre.
BAILEY V.C. and DAVIES M.B.
Abstract (from CDS):
We simulate collisions involving red giant stars in the centre of our Galaxy. Such encounters may explain the observed paucity of highly luminous red giants within ∼0.2pc of Sgr A*. The masses of the missing stars are likely to be in the range ∼2-8M☉. Recent models of the density distribution and velocity dispersion of the Galactic Centre cluster are used to calculate two-body collision rates. In particular, we use stellar-evolution models to calculate the number of collisions a star will have during different evolutionary phases. We find that the number of two-body collisions per star is ≲1 in the central 0.1-0.2pc, depending strongly on the Galactocentric radius, with some uncertainty from the assumed cluster models and stellar-evolution models. Using a 3D numerical hydrodynamics code (SPH), we simulate encounters involving cluster stars of various masses with a 2-M☉ red giant and an 8-M☉ red giant. The instantaneous mass loss in such collisions is rarely enough to destroy either giant. A fraction of the collisions do, however, lead to the formation of common-envelope systems where the impactor and core of the giant are enshrouded by the envelope of the giant. Such systems may evolve to expel the envelope, leaving a tight binary; the original giant is destroyed. The fraction of collisions that produce common-envelope systems is sensitive to the local velocity dispersion and hence Galactocentric radius. Whereas most of our collisions lead to common-envelope formation at a few parsecs from Sgr A*, very few collisions do so within the central 0.2pc. Using our collision-rate calculations, we then compute the time-scales for a giant star to suffer such a collision within the Galactic Centre. These time-scales are ≳109–10yr, and so are longer than the lifetimes of stars more massive than ∼2M☉. Thus the observed paucity of luminous giants is unlikely to be caused by the formation of common-envelope systems as a result of two-body encounters involving giant stars.
Abstract Copyright:
1999 RAS
Journal keyword(s):
celestial mechanics, stellar dynamics - Galaxy: centre
Simbad objects:
2
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