Messier 15

Messier 15

Messier 15
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]

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 1
  • Amateur astronomy 2
  • X-ray sources 3
  • Images 4
  • See also 5
  • References 6
  • External links 7


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.


See also


  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin 849 (849): 11–14.  
  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.  
  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.  
  4. ^ Marks, Michael; Kroupa, Pavel (August 2010). "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way".   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.  
  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.  
  8. ^ "SIMBAD Astronomical Database". Results for NGC 7078. Retrieved 2006-11-16. 
  9. ^ a b c d
  10. ^ Gerssen, J; van der Marel, R P; Gebhardt, K; Guhathakurta, P; Peterson, R C; Pryor, C (2003). Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15. II. Kinematic Analysis and Dynamical Modeling"Hubble Space Telescope" (PDF).  
  11. ^ Cohen, J. G.; Gillett, F. C. (1989). "The peculiar planetary nebula in M22".  
  12. ^
  13. ^ Forman W; Jones C; Cominsky L; Julien P; Murray S; Peters G (1978). "The fourth Uhuru catalog of X-ray sources".  
  14. ^ White NE; Angelini L (2001). "The discovery of a second luminous low-mass X-ray binary in the globular cluster M15".  

External links

  • Messier 15, SEDS Messier pages
  • Messier 15, Galactic Globular Clusters Database page
  • Globular Cluster Photometry With the Hubble Space Telescope. V. WFPC Study of M15's Central density Cusp
  • SDSS image of M15
  • Gretton, Roy; Gray, Meghan. "M15 – Globular Cluster". Deep Sky Videos.  
  • Messier 15 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images