Messier 15 | |
---|---|
Observation data ( J2000 epoch) | |
Class | IV [1] |
Constellation | Pegasus |
Right ascension | 21h 29m 58.33s [2] |
Declination | +12° 10′ 01.2″ [2] |
Distance | 35.69 ± 0.43 kly (10.944 ± 0.131 kpc) [3] |
Apparent magnitude (V) | 6.2 [4] |
Apparent dimensions (V) | 18′.0 |
Physical characteristics | |
Mass | 5.6×105 [5] M☉ |
Radius | ~88 ly [6] |
VHB | 15.83 |
Metallicity | = –2.37 [7] dex |
Estimated age | 12.0 Gyr [8] |
Notable features | steep central cusp |
Other designations | NGC 7078, GCl 120 [9] |
Messier 15 or M15 (also designated NGC 7078 and sometimes known as the Great Pegasus Cluster) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764.[ citation needed] At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters. [10]
M 15 is about 35,700 light-years from Earth, [3] and 175 light-years in diameter. [11] It has an absolute magnitude of −9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as " core collapse" and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole. [12]
Home to over 100,000 stars, [11] the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15-C. It also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. [13] [14] Just three others have been found in globular clusters since then. [15]
At magnitude 6.2, M15 approaches naked eye visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star. [11] [14] Telescopes with a larger aperture (at least 6 in. (150 mm)) will start to reveal individual stars, the brightest of which are of magnitude +12.6. The cluster appears 18 arc minutes in size (three tenths of a degree across). [11] M15 is around 4° WNW of the brightest star of Pegasus, Epsilon Pegasi. [14]
Earth-orbiting satellites Uhuru and Chandra X-ray Observatory have detected two bright X-ray sources in this cluster: Messier 15 X-1 (4U 2129+12) and Messier 15 X-2. [16] [17] The former appears to be the first astronomical X-ray source detected in Pegasus.
Messier 15 | |
---|---|
Observation data ( J2000 epoch) | |
Class | IV [1] |
Constellation | Pegasus |
Right ascension | 21h 29m 58.33s [2] |
Declination | +12° 10′ 01.2″ [2] |
Distance | 35.69 ± 0.43 kly (10.944 ± 0.131 kpc) [3] |
Apparent magnitude (V) | 6.2 [4] |
Apparent dimensions (V) | 18′.0 |
Physical characteristics | |
Mass | 5.6×105 [5] M☉ |
Radius | ~88 ly [6] |
VHB | 15.83 |
Metallicity | = –2.37 [7] dex |
Estimated age | 12.0 Gyr [8] |
Notable features | steep central cusp |
Other designations | NGC 7078, GCl 120 [9] |
Messier 15 or M15 (also designated NGC 7078 and sometimes known as the Great Pegasus Cluster) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764.[ citation needed] At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters. [10]
M 15 is about 35,700 light-years from Earth, [3] and 175 light-years in diameter. [11] It has an absolute magnitude of −9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as " core collapse" and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole. [12]
Home to over 100,000 stars, [11] the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15-C. It also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. [13] [14] Just three others have been found in globular clusters since then. [15]
At magnitude 6.2, M15 approaches naked eye visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star. [11] [14] Telescopes with a larger aperture (at least 6 in. (150 mm)) will start to reveal individual stars, the brightest of which are of magnitude +12.6. The cluster appears 18 arc minutes in size (three tenths of a degree across). [11] M15 is around 4° WNW of the brightest star of Pegasus, Epsilon Pegasi. [14]
Earth-orbiting satellites Uhuru and Chandra X-ray Observatory have detected two bright X-ray sources in this cluster: Messier 15 X-1 (4U 2129+12) and Messier 15 X-2. [16] [17] The former appears to be the first astronomical X-ray source detected in Pegasus.