# Messier 92

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] It was inadvertently rediscovered by Charles Messier in 1781[a] and added as the 92nd entry in his catalogue.[9] It is about 26,700 light-years away from the solar system.

Messier 92
Center of M92 by HST; 1.44′ view
Observation data (J2000 epoch)
ClassIV[1]
ConstellationHercules
Right ascension17h 17m 07.39s[2]
Declination+43° 08′ 09.4″[2]
Distance26.7×103 ly (8.2 kpc)[3]
Apparent magnitude (V)+6.3[4]
Apparent dimensions (V)14' arc minutes
Physical characteristics
Mass2.0×105[5] M
Metallicity${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –2.32[6] dex
Estimated age14.2 ± 1.2 Gyr[7]
Other designationsM92, NGC 6341, GCl 59[4]

It is one of the brighter of its sort in apparent magnitude in the northern hemisphere and in its absolute magnitude in the galaxy, but it is often overlooked by amateur astronomers due to angular proximity to bright cluster Messier 13, about 20% closer. It is visible to the naked eye under very good conditions.[10]

It is also one of the galaxy's oldest clusters. It is around 16×103 ly (4.9 kpc) above/below the galactic plane and 33×103 ly (10 kpc) from the Galactic Center.[11] The half-light radius, or radius containing the upper half of its light emission, is 1.09 arcminutes (′), while the tidal radius, the broadest standard measure, is 15.17′. It appears only slightly flattened: its minor axis is about 89% ± 3% of the major.[3]

Characteristic of other globulars, it has little of the elements other than hydrogen and helium; astronomers term this low metallicity. Specifically, relative to the Sun, its iron abundance is [Fe/H] = –2.32 dex,[11] which is 0.5% of 1.0, on this logarithmic scale, the solar abundance.[12] This puts the estimated age range for the cluster at 11 ± 1.5 billion years.[13]

The cluster is not yet in, nor guaranteed to undergo, core collapse and the core radius figures as 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.[14] 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.[15]

## References and footnotes

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, S2CID 119183070
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 "M 92". SIMBAD. Centre de données astronomiques de Strasbourg. 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, S2CID 118652005. 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, S2CID 51825384.
7. ^ 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, S2CID 13160815
8. ^ Kanas, Nick (2007), Star maps: history, artistry, and cartography, Springer-Praxis books in popular astronomy, Springer, p. 180, ISBN 978-0387716688
9. ^ Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 131, ISBN 978-0521598897
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, S2CID 15452502
12. ^ Since 10−2.29 = 0.00513.
13. ^ Di Cecco, A.; Becucci, R.; Bono, G.; Monelli, M.; Stetson, P. B.; Degl'Innocenti, S.; Moroni, P. G. Prada; Nonino, M.; Weiss, A.; Buonanno, R.; Calamida, A. (2010-06-27). "On the absolute age of the Globular Cluster M92". Publications of the Astronomical Society of the Pacific. 122 (895): 991–999. arXiv:1006.5217. doi:10.1086/656017.
14. ^ Kopacki, G. (2003), "Variable stars in the globular cluster M 92", Astronomy and Astrophysics, 369 (3): 862–870, arXiv:astro-ph/0211042, Bibcode:2001A&A...369..862K, doi:10.1051/0004-6361:20010155, S2CID 116811988
15. ^ Lu, Ting-Ni; et al. (August 2011), "Chandra and HST Studies of the X-Ray Sources in Galactic Globular Cluster M92" (PDF), The Astrophysical Journal, 736 (2): 158, Bibcode:2011ApJ...736..158L, doi:10.1088/0004-637X/736/2/158, hdl:1721.1/95659
16. ^ "All that glitters". www.spacetelescope.org. ESA/Hubble. Retrieved 8 December 2014.
1. ^ On March 18