Messier 15 or M15 (also designated NGC 7078 and sometimes known as the Great Pegasus Cluster) is a globular cluster. It is located in the constellation Pegasus.
M 15 is about 35,700 light-years from Earth, and 175 light-years in diameter. It has an absolute magnitude of −9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as “core collapse.” It has a central density cusp. An enormous number of stars surround what may be a central black hole.
The cluster is home to over 100,000 stars. It is notable for containing a large number of variable stars (112) and pulsars (8). One of these pulsars includes a double neutron star system, M15-C. It also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then.
