After its discovery with the Hubble Space Telescope, the super-dense dwarf galaxy was observed with Chandra. Inside it, Chandra spotted a bright x-ray source which may indicate the presence of a central supermassive black hole 10 million times more massive than our sun.
Since supermassive black holes aren't found in star clusters that we know formed as star clusters, then it's very likely that, if the x-ray source is in fact a SMBH, M60-UCD1 was once an enormous galaxy up to 200 times more massive than it is now - but its stars were lost in a galactic collision at some point.
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"We think nearly all of the stars have been pulled away from the exterior of what once was a much bigger galaxy," said co-author Duncan Forbes of Swinburne University in Australia. "This leaves behind just the very dense nucleus of the former galaxy, and an overly massive black hole."
Estimated to be about 10 billion years old, M60-UCD1′s tragic star stripping event may have taken place fairly early in its evolution, leaving it in its diminished state for the past several billion years.
(I wonder what the statute of limitations is on grand stellar larceny?)
The results of this study are online and have been published in the September 20th issue of Astrophysical Journal Letters.
Source: Chandra X-ray Observatory
Image credits: X-ray: NASA/CXC/MSU/J.Strader et al, Optical: NASA/STScI