Messier Index/M15

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M15
M15 - Hubble 1998.jpg
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)
Class IV
Constellation Pegasus
Right ascension 21h 29m 58.38s[1]
Declination +12° 10′ 00.6″[1]
Distance 33.6 kly (10.3 kpc)
Apparent magnitude (V) +6.2
Apparent dimensions (V) 18′.0
Physical characteristics
Mass - kg (- M{\odot})
Radius ~88 ly[2]
VHB 15.83
Estimated age -
Notable features steep central cusp
Other designations NGC 7078, GCl 120[1]

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 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.[1]

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.

External links

References

  1. a b c "SIMBAD Astronomical Database". Results for NGC 7078. http://simbad.u-strasbg.fr/Simbad. Retrieved 2006-11-16. 
  2. distance × sin( diameter_angle / 2 ) = 88 ly. radius