Most Crowded Galaxy Discovered, Only 54 Million Light Years Away

Packed with an extraordinary number of stars, M60-UCD1 is an ultra-compact dwarf galaxy 54 million light years from Earth. It was discovered with NASA's Hubble Space Telescope and follow-up observations were done with NASA's Chandra X-ray Observatory and ground-based optical telescopes. Credit: X-ray: NASA/CXC/MSU/J.Strader et al, Optical: NASA/STScI
Packed with an extraordinary number of stars, M60-UCD1 (seen in the insert) is an ultra-compact dwarf galaxy 54 million light years from Earth residing near the giant elleptical galaxy M60. It was discovered with NASA’s Hubble Space Telescope and follow-up observations were done with NASA’s Chandra X-ray Observatory and ground-based optical telescopes. Credit: X-ray: NASA/CXC/MSU/J.Strader et al, Optical: NASA/STScI

Astronomers have discovered the densest galaxy ever seen, and at 54 million light years away, it’s in our galactic neighborhood.

Using the combined imaging capabilities of ground-based observatories with the high-flying Hubble Space Telescope and its cousin, the Chandra X-Ray Observatory, the ultra-compact dwarf galaxy known as M60-UCD1 turns out to be 15,000 times denser than what is found in our own galaxy, the Milky Way.

“Traveling from one star to another would be a lot easier in M60-UCD1 than it is in our galaxy, but it would still take hundreds of years using present technology,” said lead author of the new study, astronomer Michigan State University’s Jay Strader, in  a press release.

What’s even more remarkable about M60-USD1 is that the galaxy’s most crowded part–its core, where half its 200 million solar masses resides–spans a radius of only 80 light years. That means the stars in this little galaxy are about 25 times  closer to each other than those we find around the Sun’s galactic neighborhood.

Chandra observations have revealed that the galaxy’s tiny core harbors a strong x-ray source, which belongs to a giant black hole that weighs 10 million times the mass of our sun. That makes it about twice the size of the black hole in our own galaxy.

Astronomers theorize that a close encounter with a neighboring galaxy billions of years ago may have ripped away stars from M60-USD1 and may have led to the supermassive black hole pulling in the surviving stars close together.

“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 in the press release.

“This leaves behind just the very dense nucleus of the former galaxy, and an overly massive black hole.”

Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.

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