An Ultra-Compact Dwarf Galaxy

Astronomers may have discovered the densest galaxy in the nearby Universe. The galaxy, known as M60-UCD1, is located about 54 million light years from Earth. M60-UCD1 is packed with an extraordinary number of stars and this has led scientists to classify it as an "ultra-compact dwarf galaxy." This means that this galaxy is smaller and has more stars than just a regular dwarf galaxy. While astronomers already knew this, it wasn't until these latest results from Chandra, Hubble and telescopes on the ground that they knew just how dense this galaxy truly is. M60-UCD1 has the mass about 200 million times our sun and, remarkably, about half of this mass is packed into a radius of just about 80 light years. That translates into the density of stars in this part of M60-UCD1 being about 15,000 times greater than what's found in Earth's neighborhood in the Milky Way. Astronomers have been trying to determine where these ultra-compact dwarf galaxies fit into the galactic evolutionary chain. Some have suggested they start off not as galaxies but as giant star clusters. The latest results on M60-UCD1 challenge that idea. The new Chandra data indicate that there may be a supermassive black hole at the center of M60-UCD1. If that's the case, then it's unlikely this object could have ever been a star cluster. Instead, the X-ray data point to this galaxy being the remnants of a larger galaxy that had its outer stars ripped away by tidal forces, leaving behind the dense inner core of the galaxy. Other information about M60-UCD1 including its large mass, point to the same conclusion. Regardless, this galaxy is a fascinating object that astronomers will be studying for a long time to come.

Credit: NASA/CXC/A. Hobart