A new globular cluster black hole in NGC 4472
  We discuss CXOU~1229410+075744, a new black hole candidate in a globular
cluster in the elliptical galaxy NGC~4472. By comparing two Chandra
observations of the galaxy, we find a source that varies by at least a factor
of 4, and has a peak luminosity of at least $2\times10^{39}$ ergs/sec. As such,
the source varies by significantly more than the Eddington luminosity for a
single neutron star, and is a strong candidate for being a globular cluster
black hole. The source's X-ray spectrum also evolves in a manner consistent
with what would be expected from a single accreting stellar mass black hole. We
consider the properties of the host cluster of this source and the six other
strong black hole X-ray binary candidates, and find that there is suggestive
evidence that black hole X-ray binary formation is favored in bright and metal
rich clusters, just as is the case for bright X-ray sources in general.
