Messier 15 or M15 (also designated NGC 7078) is a w:globular cluster in the w:constellation Pegasus. It was discovered by w:Jean-Dominique Maraldi in w:1746 and included in w:Charles Messier's catalogue of w:comet-like objects in w:1764. At an estimated 13.2 billion years old, it is one of the oldest known globular clusters.
M15 photographed by Hubble Space Telescope. The planetary nebula Pease 1 can be seen as a fuzzy reddish object near the upper left of this image.
|Observation data (J2000 epoch)|
|Right ascension||21h 29m 58.38s|
|Declination||+12° 10′ 00.6″|
|Distance||33.6 kly (10.3 kpc)|
|Apparent magnitude (V)||+6.2|
|Apparent dimensions (V)||18′.0|
|Mass||- kg (- M)|
|Notable features||steep central cusp|
|Other designations||NGC 7078, GCl 120|
M15 is about 33,600 w:light-years from w:Earth. It has an w:absolute magnitude of -9.2 which translates to a total w:luminosity of 360,000 times that of the w:Sun. Messier 15 is one of the most densely packed globulars known in the w:Milky Way galaxy. Its core has undergone a contraction known as 'w:core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.
Messier 15 contains 112 w:variable stars, a rather high number. It also contains at least 8 w:pulsars, including one double w:neutron star system, M15 C. Moreover, M15 houses w:Pease 1, one of only four w:planetary nebulae known to reside within a globular cluster, which was discovered in w:1928.
To the amateur w:astronomer Messier 15 appears as a fuzzy star in the smallest of w:telescopes. Mid to large size telescopes (at least 6 in./150 mm diameter) will start to reveal individual stars, the brightest of which are of magnitude +12.6.
The central square arcminute of M15 imaged using the w:lucky imaging technique