It's a case of cosmic whodunit: What happened to all the external stars in M60-UCD1, an ultra-compact dwarf galaxy located 54 million light-years away, near the fringes of the bright M60 galaxy in the constellation Virgo?
Despite its diminutive title this dwarf galaxy is packing a lot of mass - over 200 million times the mass of the sun is stuffed inside it, making M60-UCD1 one of the densest local galaxies ever discovered, if not the densest.
PHOTOS: Hubble Logs Millionth Observation
What's more, over half of that mass is found within a region only 160 light-years across. Stars there are 25 times closer together than they are in our neighborhood of the Milky Way.
"Traveling from one star to another would be a lot easier in M60-UCD1 than it is in our galaxy," said Jay Strader of Michigan State University in Lansing, first author of a new paper describing these results.
The question is: how did M60-UCD1 get so dense? Did it originally form as a crowded star cluster? Or is it what's left of an even larger galaxy... one that's had its outer stars stolen away during a run-in with another galaxy?