Messier 15

From Infogalactic: the planetary knowledge core
Jump to: navigation, search
Messier 15
250px
M15 photographed by HST. The planetary nebula Pease 1 can be seen as a small blue object to the upper left of the core of the cluster.
Observation data (J2000 epoch)
Class IV[1]
Constellation Pegasus
Right ascension 21h 29m 58.33s[2]
Declination +12° 10′ 01.2″[2]
Distance 33 kly (10 kpc)[3]
Apparent magnitude (V) +6.2
Apparent dimensions (V) 18′.0
Physical characteristics
Mass 5.6×105[4] M
Radius ~88 ly[5]
VHB 15.83
Metallicity –2.37[6] dex
Estimated age 12.0 Gyr[7]
Notable features steep central cusp
Other designations NGC 7078, GCl 120[8]
See also: Globular cluster, List of globular clusters

Messier 15 or M15 (also designated NGC 7078) 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. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters.

Characteristics

M15 is about 33,600 light-years from Earth, and 175 light years in diameter.[9] 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.[10]

Home to over 100,000 stars,[9] the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15 C. M15 also contains Pease 1, the first planetary nebula discovered within a globular cluster[11] in 1928. Just three others have been found in globular clusters since then.[12]

Amateur astronomy

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.[9] Telescopes with a larger aperture (at least 6 in./150 mm diameter) will start to reveal individual stars, the brightest of which are of magnitude +12.6. The cluster appears 18 arc minutes in size.[9]

X-ray sources

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.[13][14] The former appears to be the first astronomical X-ray source detected in Pegasus.

Images

See also

References

  1. Lua error in package.lua at line 80: module 'strict' not found.
  2. 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
  3. Lua error in package.lua at line 80: module 'strict' not found.
  4. Lua error in package.lua at line 80: module 'strict' not found. Mass is from MPD on Table 1.
  5. distance × sin( diameter_angle / 2 ) = 88 ly radius
  6. Lua error in package.lua at line 80: module 'strict' not found.
  7. Lua error in package.lua at line 80: module 'strict' not found.
  8. Lua error in package.lua at line 80: module 'strict' not found.
  9. 9.0 9.1 9.2 9.3 http://www.astropix.com/HTML/SHOW_DIG/M15_Pease1.HTM
  10. Lua error in package.lua at line 80: module 'strict' not found.
  11. Lua error in package.lua at line 80: module 'strict' not found.
  12. http://messier.seds.org/more/m015_h2.html
  13. Lua error in package.lua at line 80: module 'strict' not found.
  14. Lua error in package.lua at line 80: module 'strict' not found.

External links

Coordinates: Sky map 21h 29m 58.38s, 12° 10′ 00.6″