Messier 72

Messier 72 (also known as M72 or NGC 6981) is a globular cluster in the Aquarius constellation discovered by French astronomer Pierre Méchain on August 29, 1780. French astronomer Charles Messier looked for it on the following October 4, and included it in his catalog.[4] Both decided that it was a faint nebula rather than a cluster. With a larger instrument, British astronomer John Herschel called it a bright "cluster of stars of a round figure". American astronomer Harlow Shapley noted a similarity to Messier 4 and Messier 12.[8]

Messier 72
M72 from Hubble Space Telescope; 3.44′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
ClassIX[1]
ConstellationAquarius
Right ascension 20h 53m 27.70s[2]
Declination–12° 32′ 14.3″[2]
Distance54.57 ± 1.17 kly (16.73 ± 0.36 kpc)[3]
Apparent magnitude (V)9.35[4]
Apparent dimensions (V)6.6'
Physical characteristics
Mass1.68×105[5] M☉
Metallicity = –1.48 ± 0.03[3] dex
Estimated age9.5 Gyr[6]
Other designationsNGC 6981, GCl 118[7]

This cluster is visible as a faint nebula in a telescope with a 6 cm (2.4 in) aperture. the surrounding field stars become visible at 15 cm (5.9 in), while 25 cm (9.8 in) is sufficient to resolve the cluster with an angular diameter of 2.5′. At 30 cm (12 in) the core is resolved in a 1.25′ diameter, showing a broad spread with darker regions to the south and east.[9]

Based upon a 2011 census of variable stars, Messier 72 is located at a distance of 54.57 ± 1.17 kly (16.73 ± 0.36 kpc) from the Sun.[3] It has an estimated combined mass equal to 168,000[5] times the mass of the Sun and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times the luminosity of the Sun per cubic parsec.[6] There are 43 identified variable stars in the cluster.[3]

Map showing location of M72

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. 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. Figuera Jaimes, R.; et al. (October 2011), Henney, W. J.; Torres-Peimbert, S. (eds.), "XIII Latin American Regional IAU Meeting", Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias), 40, pp. 235–236, Bibcode:2011RMxAC..40..235F. |contribution= ignored (help)
  4. Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 266, ISBN 978-0521598897
  5. 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.
  6. Sollima, A.; et al. (April 2008), "The correlation between blue straggler and binary fractions in the core of Galactic globular clusters", Astronomy and Astrophysics, 481 (3): 701–704, arXiv:0801.4511, Bibcode:2008A&A...481..701S, doi:10.1051/0004-6361:20079082
  7. "NGC 6981". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
  8. Burnham, Robert (1978), Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Dover Books on Astronomy Series, 1 (2nd ed.), Courier Dover Publications, pp. 188–189, ISBN 978-0486235677
  9. Luginbuhl, Christian B.; Skiff, Brian A. (1998), Observing Handbook and Catalogue of Deep-Sky Objects (2nd ed.), Cambridge University Press, p. 25, ISBN 978-0521625562

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