Astronomers using NASA’s Hubble Space Telescope, Chandra X-ray Observatory and ground-based optical telescopes have discovered what they say is the densest galaxy in the nearby Universe.
The ultra-compact dwarf galaxy M60-UCD1 is located near a massive elliptical galaxy Messier 60. Image credit: X-ray – NASA / CXC / MSU / J.Strader et al; optical – NASA / STScI.
The galaxy, dubbed M60-UCD1, is located near the elliptical galaxy Messier 60 about 54 million light years away.
“This galaxy is more massive than any ultra-compact dwarfs of comparable size and is arguably the densest galaxy known in the local Universe,” said Dr Jay Strader of the Michigan State University, lead author of a paper published in the Astrophysical Journal Letters (arXiv.org).
M60-UCD1 weighs more than 200 million Suns, over half of which is concentrated within a radius of just 80 light years. The density of stars in that region is 15,000 times greater than found in Earth’s neighborhood in the Milky Way.
“Traveling from one star to another would be a lot easier in M60-UCD1 than it is in our galaxy. Since the stars are so much closer in this galaxy, it would take just a fraction of the time,” Dr Strader said.
This image shows the galaxy M60-UCD1. Image credit: NASA / STScI.
Another intriguing aspect of M60-UCD1 is the presence of a bright X-ray source in its center. One explanation for this is a giant black hole weighing in at some 10 million times the mass of our Sun.
The scientists are trying to determine if M60-UCD1 and other ultra-compact dwarf galaxies are either born as really jam-packed star clusters or if they are galaxies that get smaller because they have stars ripped away from them. The possible massive black hole, combined with the high galaxy mass and Sun-like levels of elements found in the stars, favor the latter idea.
A giant black hole at the center of M60-UCD1 helps tip the scales against the scenario where this galaxy was once a star cluster, since such large black holes are not found in these types of objects.
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Bibliographic information: Jay Strader et al. 2013. The Densest Galaxy. ApJ 775, L6; doi: 10.1088/2041-8205/775/1/L6
