Astronomers have discovered evidence of what they believe is the most crowded galaxy near Earth.
The new “ultra-compact” galaxy, named M60-UCD1, is home to an extraordinary number of stars and it is expected to provide scientists with clues to its intriguing past and its role in galactic evolution, according to the astronomers who made the discovery by using NASA's Hubble Space Telescope and the Chandra X-ray Observatory.
According to the astronomers, the most remarkable aspect of M60-UCD1 is that about half of its mass is found within a radius of only about 80 light years, while the density of stars within it is about 15,000 times greater -- meaning the stars are about 25 times closer to each other -- than in the Milky Way galaxy.
"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 Jay Strader of Michigan State University, who is the lead author of the study published on Sept. 20 in The Astrophysical Journal Letters.
According to a NASA statement, the M60-UCD1 galaxy is estimated to be about 10 billion years old and is located near another massive elliptical galaxy called NGC 4649, or M60, which is about 54 million light years from Earth.
Observations from a 10-meter telescope at the W.M. Keck Observatory in Hawaii revealed that M60-UCD1 is the brightest known galaxy of its type and one of the most massive, weighing 200 million times more than the sun.
Scientists said that the stars in M60-UCD1 have an abundance of elements heavier than hydrogen and helium, a trait that makes it “a fertile environment for planets and, potentially, for life to form.”
Data provided by the Chandra Observatory revealed yet another intriguing aspect of M60-UCD1 -- a bright X-ray source in its center that hints at a giant black hole weighing in at about 10 million times the mass of the sun.
Astronomers now want to understand whether M60-UCD1 was born as a jam-packed star cluster as the possible existence of a giant black hole is atypical of star clusters, which usually do not have large black holes in them. So, if the X-ray source is in fact due to a massive black hole, it was likely produced by collisions between M60-UCD1 and one or more nearby galaxies.
Thanks to M60-UCD1's great mass and the abundance of heavy elements, scientists have not ruled out a theory that it is the remnant of a much larger galaxy. If M60-UCD1 did peel away from a bigger galaxy, then its original size could have been 50 to 200 times more massive than it is now, according to astronomers.
“We think nearly all of the stars have been pulled away from the exterior of what once was a much bigger galaxy,” Duncan Forbes of Swinburne University in Australia and a co-author of the study said in a statement. “This leaves behind just the very dense nucleus of the former galaxy, and an overly massive black hole.”