Messier 15 is one of the densest star clusters in our galaxy -- and one of the most mysterious.
The globular star cluster is plainly visible with binoculars, but it's a tall order to capture clearly in a single photograph. After all, the cluster contains more than 100,000 stars, a planetary nebula, and a possible black hole. But now the Hubble Space Telescope has accomplished that feat. NASA and the European Space Agency delivered the best-yet image of the Messier 15 on Nov. 14.
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This stunning image of Messier 15, or M15 , is part of the agencies' Hubblecast video project. See that bright blue dot near the center, on the upper left? That's the star cluster's planetary nebula, Pease 1.
Located 35,000 light-years away from Earth in the constellation Pegasus, Messier 15 is also one of the oldest globular clusters known to astronomers. The spherical group of stars orbits the center of the Milky Way. Most of its mass is located near its core, which may contain a rare type of black hole.
Since astronomers first began studying the cluster, they've speculated that -- at it's heart -- Messier 15 contains either a group of neutron stars or an intermediate-mass black hole. It's the latter, which scientists say is more likely, that is the most intriguing.
In the past, astronomers did not believe that such mid-size black holes existed. But recent evidence from Hubble and other observatories have led researchers to think otherwise. By studying this particular type of black hole, astronomers may learn more about how the mysterious objects form and evolve.
Watch NASA/ESA's video tour of Messier 15 below that reveals what Hubble has learned from star clusters.