Jean-Dominique Maraldi discovered M15 in 1746 while searching for comets. Today it is known as an old globular cluster roughly 34,000 light-years away in Pegasus. Its stars become dramatically more concentrated toward the center, making the cluster a classic example of the dense stellar environments that globular clusters can create.
M15 also contains Pease 1, a planetary nebula discovered in 1928. Planetary nebulae are rare inside globular clusters, so finding the remains of a dying star embedded in such an ancient stellar population gives M15 an unusual second identity.
Studies of the cluster’s crowded core have also been used to investigate whether an intermediate-mass black hole may reside there. The central dynamics are difficult to untangle, which makes M15 not merely a beautiful object but an active astrophysical laboratory.
At the eyepiece all of that begins as a small round glow. Knowing what is packed into that glow changes the view.
Sources: NASA Hubble Messier Catalog, “Messier 15”; NASA Hubble studies of the M15 core.
