Celestial hemisphere:  Northern  ·  Constellation: Pegasus (Peg)  ·  Contains:  M 15  ·  NGC 7078  ·  PGC 1403128  ·  PGC 1407648  ·  PGC 1408577  ·  PGC 66827  ·  PK065-27.1  ·  PK065-27.2
M15 Great Pegasus Cluster, Jerry Macon
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M15 Great Pegasus Cluster

M15 Great Pegasus Cluster, Jerry Macon
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M15 Great Pegasus Cluster

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Description

Messier 15 (M15), also known as the Great Pegasus Cluster, is a globular cluster located in the northern constellation Pegasus.

The cluster has an apparent magnitude of 6.2 and lies at a distance of 33,600 light years (10,000 parsecs) from Earth. It has the designation NGC 7078 in the New General Catalogue.

Messier 15 is one of the oldest known globulars in our galaxy. It has an estimated age of 12 billion years and only 1 percent of the Sun’s iron content. The cluster has an absolute magnitude of -9.2, which makes it about 360,000 times more luminous than the Sun.

Messier 15 has an apparent diameter of 18 arc minutes, corresponding to a linear diameter of about 175 light years.

The tidal radius of M15 spans 21.5 arc minutes, or about 210 light years from the cluster’s centre.

Messier 15 has a density classification IV and is one of the most densely concentrated clusters of its kind. The cluster is notable for its steep central cusp, with an exceptionally large number of stars orbiting what is likely a central black hole.

The central density cusp is a result of the cluster having undergone a core collapse, a contraction of its core region. This is a common occurrence in globular clusters as they evolve: Messier 30 and Messier 70 also contain a collapsed core. A total of 21 of the 157 known globular clusters in the Milky Way, and possibly 8 more, including Messier 62 and Messier 79, have undergone a core collapse.

The core of Messier 15 is very small – about 0.14 arc minutes or 1.4 light years – compared to the cluster’s size. Half the cluster’s mass is concentrated within the central 10 light years, or 1.06 arc minutes. Scientists have theorized that either the cluster contains a supermassive black hole at its core or the concentration of mass is a result of the gravitational interaction of the stars in this area. A survey of the cluster’s inner 22 light years alone revealed about 30,000 stars.

The cluster contains more than 100,000 stars, including a considerable number of variables (112) and pulsars (8), neutron stars formed in supernova explosions that occurred when M15 and the universe itself were still young. The only other globulars with more known variables are Messier 3 and Omega Centauri. Omega Centauri, the largest globular cluster in the Milky Way Galaxy, is not included in Messier’s catalogue.

The brightest stars in M15 are of magnitude 12.6. They have an absolute magnitude of -2.8, which makes them about 1,000 times more luminous than the Sun. M15 is approaching us at 107 km/s.

Messier 15 is home to a double neutron star system, designated M15 C, and the first ever planetary nebula discovered in a globular cluster.
(messier-objects.com)

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M15 Great Pegasus Cluster, Jerry Macon

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