Open main menu

Wikipedia β

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.

Messier 15
New Hubble image of star cluster Messier 15.jpg
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

Contents

CharacteristicsEdit

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 astronomyEdit

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 sourcesEdit

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.

ImagesEdit

See alsoEdit

ReferencesEdit

  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849 (849): 11–14. Bibcode:1927BHarO.849...11S. 
  2. ^ a b Goldsbury, Ryan; et al. (December 2010). "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters". The Astronomical Journal. 140 (6): 1830–1837. arXiv:1008.2755 . Bibcode:2010AJ....140.1830G. doi:10.1088/0004-6256/140/6/1830. 
  3. ^ Hessels, J. W. T.; et al. (November 2007). "A 1.4 GHz Arecibo Survey for Pulsars in Globular Clusters". The Astrophysical Journal. 670 (1): 363–378. arXiv:0707.1602 . Bibcode:2007ApJ...670..363H. doi:10.1086/521780. 
  4. ^ Marks, Michael; Kroupa, Pavel (August 2010). "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way". Monthly Notices of the Royal Astronomical Society. 406 (3): 2000–2012. arXiv:1004.2255 . Bibcode:2010MNRAS.406.2000M. doi:10.1111/j.1365-2966.2010.16813.x.  Mass is from MPD on Table 1.
  5. ^ distance × sin( diameter_angle / 2 ) = 88 ly radius
  6. ^ Boyles, J.; et al. (November 2011). "Young Radio Pulsars in Galactic Globular Clusters". The Astrophysical Journal. 742 (1): 51. arXiv:1108.4402 . Bibcode:2011ApJ...742...51B. doi:10.1088/0004-637X/742/1/51. 
  7. ^ Koleva, M.; et al. (April 2008). "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting". Monthly Notices of the Royal Astronomical Society. 385 (4): 1998–2010. arXiv:0801.0871 . Bibcode:2008MNRAS.385.1998K. doi:10.1111/j.1365-2966.2008.12908.x 
  8. ^ "SIMBAD Astronomical Database". Results for NGC 7078. Retrieved 2006-11-16. 
  9. ^ a b c d http://www.astropix.com/HTML/SHOW_DIG/M15_Pease1.HTM
  10. ^ Gerssen, J; van der Marel, R P; Gebhardt, K; Guhathakurta, P; Peterson, R C; Pryor, C (2003). "Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15. II. Kinematic Analysis and Dynamical Modeling" (PDF). Astronomical Journal. 125 (1): 376–377. arXiv:astro-ph/0210158 . Bibcode:2003AJ....125..376G. doi:10.1086/345574. 
  11. ^ Cohen, J. G.; Gillett, F. C. (1989). "The peculiar planetary nebula in M22". Astrophysical Journal. 346: 803–807. Bibcode:1989ApJ...346..803C. doi:10.1086/168061. 
  12. ^ http://messier.seds.org/more/m015_h2.html
  13. ^ Forman W; Jones C; Cominsky L; Julien P; Murray S; Peters G (1978). "The fourth Uhuru catalog of X-ray sources". Astrophysical Journal Supplement Series. 38: 357. Bibcode:1978ApJS...38..357F. doi:10.1086/190561. 
  14. ^ White NE; Angelini L (2001). "The discovery of a second luminous low-mass X-ray binary in the globular cluster M15". Astrophysical Journal Letters. 561 (1): L101–5. arXiv:astro-ph/0109359 . Bibcode:2001ApJ...561L.101W. doi:10.1086/324561. 

External linksEdit