# Messier 92

Messier 92
Center of M92 by HST; 1.44′ view
Observation data (J2000 epoch)
Class IV[1]
Constellation Hercules
Right ascension 17h 17m 07.39s[2]
Declination +43° 08′ 09.4″[2]
Distance 26.7×103 ly (8.2 kpc)[3]
Apparent magnitude (V) +6.3[4]
Apparent dimensions (V) 14' arc minutes
Physical characteristics
Mass 2.0×105[5] M
Metallicity ${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –2.16[6] dex
Estimated age 14.2 ± 1.2 Gyr[7]
Other designations M92, NGC 6341, GCl 59[4]

Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules. It was discovered by Johann Elert Bode in 1777, then published in the Jahrbuch during 1779.[8] The cluster was independently rediscovered by Charles Messier on March 18, 1781 and added as the 92nd entry in his catalogue.[9] M92 is at a distance of about 26,700 light-years away from Earth.

M92 is one of the brighter globular clusters in the northern hemisphere, but it is often overlooked by amateur astronomers because of its proximity to the even more spectacular Messier 13. It is visible to the naked eye under very good conditions.[10]

Among the Milky Way population of globular clusters, Messier 92 is among the brighter clusters in terms of absolute magnitude. It is also one of the oldest clusters. Messier 92 is located around 16×103 ly (4.9 kpc) above the galactic plane and 33×103 ly (10 kpc) from the Galactic Center.[11] The heliocentric distance of Messier 92 is 26.7×103 ly (8.2 kpc). The half-light radius, or radius containing half of the light emission from the cluster, is 1.09 arcminutes, while the tidal radius is 15.17 arcminutes. It appears only slightly flattened, with the minor axis being about 89% ± 3% as large as the major axis.[3]

Characteristic of other globulars, Messier 92 has a very low abundance of elements other than hydrogen and helium; what astronomers term its metallicity. Relative to the Sun, the abundance of iron in the cluster is given by [Fe/H] = –2.29 dex,[11] which equates to only 0.5% of the solar abundance.[12] This puts the estimated age range for the cluster at 14.2 ± 1.2 billion years, or roughly the age of the Universe.[7]

The cluster is not currently in a state of core collapse and the core radius is about 2 arcseconds.[11] It is an Oosterhoff type II (OoII) globular cluster, which means it belongs to the group of metal poor clusters with longer period RR Lyrae variable stars. The 1997 Catalogue of Variable Stars in Globular Clusters listed 28 candidate variable stars in the cluster, although only 20 have been confirmed. As of 2001, there are 17 known RR Lyrae variables in Messier 92.[13] 10 X-ray sources have been detected within the 1.02 arcminute half-mass radius of the cluster, of which half are candidate cataclysmic variable stars.[14]

## References

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 [ Erratum: 2011AJ....142...66G ]", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830
3. ^ a b Chen, C. W.; Chen, W. P. (October 2010), "Morphological Distortion of Galactic Globular Clusters", The Astrophysical Journal, 721 (2): 1790–1819, Bibcode:2010ApJ...721.1790C, doi:10.1088/0004-637X/721/2/1790
4. ^ a b "SIMBAD Astronomical Database". Results for NGC 6341. Retrieved 2006-11-17.
5. ^ 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.
6. ^ Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x.
7. ^ a b Paust, Nathaniel E. Q.; Chaboyer, Brian; Sarajedini, Ata (June 2007), "BVI Photometry and the Luminosity Functions of the Globular Cluster M92", The Astronomical Journal, 133 (6): 2787–2798, arXiv:astro-ph/0703167, Bibcode:2007AJ....133.2787P, doi:10.1086/513511
8. ^ Kanas, Nick (2007), Star maps: history, artistry, and cartography, Springer-Praxis books in popular astronomy, Springer, p. 180, ISBN 0387716688
9. ^ Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 131, ISBN 0521598893
10. ^ Frommert, Hartmut; Kronberg, Christine (September 2, 2007), "Messier 92", SEDS, The Munich Astro Archive, retrieved 2012-04-08
11. ^ a b c Drukier, G. A.; et al. (March 2007), "The Global Kinematics of the Globular Cluster M92", The Astronomical Journal, 133 (3): 1041–1057, arXiv:astro-ph/0611246, Bibcode:2007AJ....133.1041D, doi:10.1086/510721
12. ^ Since 10−2.29 = 0.00513.
13. ^ Kopacki, G. (April 2001), "Variable stars in the globular cluster M 92", Astronomy and Astrophysics, 369 (3): 862–870, Bibcode:2001A&A...369..862K, doi:10.1051/0004-6361:20010155
14. ^ Lu, Ting-Ni; et al. (August 2011), "Chandra and HST Studies of the X-Ray Sources in Galactic Globular Cluster M92", The Astrophysical Journal, 736 (2): 158, Bibcode:2011ApJ...736..158L, doi:10.1088/0004-637X/736/2/158
15. ^ "All that glitters". www.spacetelescope.org. ESA/Hubble. Retrieved 8 December 2014.