M60-UCD1 is the Densest Galaxy Known in the Local Universe, Astronomers Say

Astronomers have found an ultra-compact galaxy in the universe using NASA's Hubble Space Telescope and Chandra X-ray Observatory. The density of this galaxy is about 15,000 times greater than Milky Way and is now considered to be the most crowded galaxy in the local universe.

Ultra-compact dwarf systems are a new class of stellar systems discovered in the last few years and astronomers are still trying to explain their origin. Many UCDs are 1/1000^th the diameter of our own galaxy- The Milky Way

According to the latest study, the newly discovered galaxy called M60-UCD1 is about 10 billion years old and is the densest galaxy ever found. M60-UCD1 was found in the Virgo cluster of galaxies, which is located about 54 million light years from our galaxy.

"This galaxy is more massive than any ultra-compact dwarfs of comparable size," said Jay Strader, Michigan State University assistant professor of physics and astronomy, "and is arguably the densest galaxy known in the local universe."

Another interesting feature of the galaxy is that roughly about half of its mass is concentrated in a space that has a radius of just 80 light years. "Traveling from one star to another would be a lot easier in M60-UCD1 than it is in our galaxy," Strader said in a news release. "Since the stars are so much closer in this galaxy, it would take just a fraction of the time." In comparison, our nearest star is the Alpha Centauri- about 4 light years away from the Sun.

Astronomers have also found that the galaxy has a very bright X-ray source at its center. They believe that the X-ray is a giant black hole, with an equivalent mass of 10 million suns put together.

The latest discovery could yield clues about the galaxy's past and how it evolved to be one of the densest known star systems.

The team isn't sure how M60-UCD1 formed. One possible explanation is that it was born as a tightly packed cluster or grew compact as stars started moving away from it. Right now, astronomers believe that the star cluster visible today is the remnant of an older, larger star cluster. The fact that the star cluster  has a great mass and has elements that are heavier than hydrogen and helium are evidence supporting the theory.

"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 a statement by NASA. "This leaves behind just the very dense nucleus of the former galaxy, and an overly massive black hole."

According to the astronomers, if M60-UCD1 is a stripped version of an older star system, then the original cluster of star would have been 50 to 200 times more massive than the current system.

The study is published in the journal Astrophysical Journal Letters.