M15
NGC 7078
Properties
Position & Identifiers
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M15 · 11.1′ diameter · N up, E left
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About M15
Description
The Great Pegasus Cluster is one of the densest globular clusters known, located about 33,600 light-years away in Pegasus. It contains over 100,000 stars packed into a sphere about 175 light-years across, with an extremely dense core that may harbor a central black hole. M15 has undergone 'core collapse' — its core has contracted to an extraordinarily dense state.
Observing Tips
Located about 4 degrees northwest of Enif (Epsilon Pegasi), the nose of the winged horse. Visible in binoculars as a bright, star-like fuzzy point. A 4-inch telescope at 100x shows a bright, intensely concentrated glow. An 8-inch telescope resolves stars in the outer regions while the core remains a brilliant, unresolved blaze. The planetary nebula Pease 1 within the cluster is visible in large amateur scopes. Best observed from August through November.
History
Discovered by Jean-Dominique Maraldi on September 7, 1746. Charles Messier cataloged it in 1764. In 1928, the planetary nebula Pease 1 was discovered within M15 — only four planetary nebulae are known in globular clusters.
Fun Facts
M15 is one of only a few globular clusters known to have undergone core collapse, where gravitational interactions cause the core to contract to extreme density. It may contain a rare intermediate-mass black hole at its center. The cluster also contains two known pulsars and an X-ray binary system — evidence of the violent stellar interactions in its ultra-dense core.