Discovered by Jean-Dominique Maraldi in 1746.
M15 is among the most conspicuous of the globular clusters. It lies at a distance of about 33,600 light years from the Earth. Its linear extension is about 175 light years, and its total visual brightness is 6.2 magnitude. It is visible using binoculars under dark skies. M15 is one of the densest of all (globular) star clusters in our Milky Way galaxy. M15's core has undergone a process of contraction called "core collapse", which is thought to be common in the dynamical evolution of globulars. Of the 150 known globular clusters within the Milky Way, 21 have been found to contain a collapsed core. It is postulated a massive black hole may lie at the center of M15's core.