Messier 15

November 29, 2019

First, what is a globular cluster? A globular cluster is a densely-packed group of stars bound by their own collective gravity. They form gradually—many of them over literally billions of years—pulling new stars in as they complete their orbits around their host galaxy. The globular we’re looking for tonight is Messier 15—also known as the Globular Cluster in Pegasus.

To find Pegasus, look high to the southwest around 8pm. Find the nose of Pegasus, the orange star Enif, which is also the brightest star in Pegasus. Then, through your telescope or binoculars, scan just to the right, and slightly downward. When you find what looks like a fuzzy star, you’ve found it. A 12 billion-year-old collection of well over 100,000 stars… that’s over 170 light-years across.

What sets Messier 15 apart from a lot of other globular clusters is that it’s theorized to have an intermediate-class black hole at its center. This type of black hole has only been discovered in the last 15 years. Before that, all we knew about were stellar-mass black holes—the small ones, and supermassive black holes—like those found at the center of galaxies. And while we don’t yet know for sure whether there’s one in Messier 15, it’ll be fun to ponder as you look at it tonight.