Messier 70

Messier 70 or M70, also known as NGC 6681, is a globular cluster of stars to be found in the south of Sagittarius.[lower-alpha 1] It was discovered by Charles Messier in 1780.[lower-alpha 2][6] The famous comet Hale–Bopp was discovered near this cluster in 1995.[10][lower-alpha 3]

Messier 70
Globular cluster Messier 70 by Hubble Space Telescope; 3.3′ view
Observation data (J2000 epoch)
ClassV[1]
ConstellationSagittarius
Right ascension18h 43m 12.76s[2]
Declination–32° 17′ 31.6″[3]
Distance29.4 kly (9.0 kpc)[4]
Apparent magnitude (V)7.9[5]
Apparent dimensions (V)8.0′[6]
Physical characteristics
Mass1.79×105[4] M☉
Radius34 ly[7]
Tidal radius11.2′[8]
Metallicity = –1.35[9] dex
Estimated age12.80 Gyr[9]
Other designationsGCl 101, M70, NGC 6681[3]

It is about 29,400[4] light years away from Earth and around 6,500 light-years[11] from the Galactic Center. It is roughly the same size and luminosity as its neighbour in space, M69.[12] M70 has a very small core radius of 0.22 ly (0.068 pc)[13] and a half-light radius of 182.0 ly (55.80 pc).[14] This cluster has undergone core collapse, leaving it centrally concentrated[15] with the luminosity distribution following a power law.[11]

There are two distinct stellar populations in the cluster, with each displaying unique abundance abundances. These likely represent different generations of stars.[16] Five known variable stars lie within the broadest radius, the tidal radius, of it, all of which are RR Lyrae variables.[8][17] The cluster may have two blue stragglers near the core.[11]

  • Image by Hubble Space Telescope
    Image by Hubble Space Telescope
  • Map showing M70, against a conventional (southern) horizon
    Map showing M70, against a conventional (southern) horizon

See also

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. 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, S2CID 119183070.
  3. "NGC 6681". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 November 2006.
  4. 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, S2CID 118649860.
  5. "Messier 70". SEDS Messier Catalog. Retrieved 30 April 2022.
  6. Adam, Len (2018), Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer, p. 304, Bibcode:2018imor.book.....A, ISBN 978-3319653853
  7. distance × sin( diameter_angle / 2 ) = 34 ly. radius
  8. Liller, M. H. (October 1983), "The variable stars in the field of the globular cluster NGC 6681", Astronomical Journal, 88: 1463–1469, Bibcode:1983AJ.....88.1463L, doi:10.1086/113435.
  9. 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.
  10. Mobberley, Martin (2013), It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore, Springer Science & Business Media, p. 483, ISBN 978-3319006093
  11. Watson, Alan M.; et al. (November 1994), "Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2" (PDF), Astrophysical Journal, Part 2, 435 (1): L55–L58, Bibcode:1994ApJ...435L..55W, doi:10.1086/187593.{{citation}}: CS1 maint: multiple names: authors list (link)
  12. Frommert, Hartmut; Kronberg, Christine (30 August 2007), "Globular Cluster M70", SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved 4 December 2018.
  13. Djorgovski, S. (January 1993), "Physical Parameters of Galactic Globular Clusters", in Djorgovski, S. G.; Meylan, G. (eds.), Structure and Dynamics of Globular Clusters. Proceedings of a Workshop held in Berkeley, California, July 15–17, 1992, to Honor the 65th Birthday of Ivan King, vol. 50, San Francisco, California: Astronomical Society of the Pacific, p. 373, Bibcode:1993ASPC...50..373D, ISBN 978-0937707692.
  14. Forbes, Duncan A.; et al. (October 2008), "Uniting old stellar systems: from globular clusters to giant ellipticals", Monthly Notices of the Royal Astronomical Society, 389 (4): 1924–1936, arXiv:0806.1090, Bibcode:2008MNRAS.389.1924F, doi:10.1111/j.1365-2966.2008.13739.x, S2CID 14108457.
  15. Pryor, Carlton; et al. (August 1989), "Mass-to-light ratios for globular clusters. I - The centrally concentrated clusters NGC 6624, M28 (NGC 6626), and M70 (NGC 6681)", Astronomical Journal, 98: 596–610, Bibcode:1989AJ.....98..596P, doi:10.1086/115160.
  16. O'Malley, Erin M.; et al. (September 2017), "High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681", The Astrophysical Journal, 846 (1): 15, arXiv:1706.06962, Bibcode:2017ApJ...846...23O, doi:10.3847/1538-4357/aa7b72, S2CID 118972140, 23.
  17. Clement, Christine M.; et al. (November 2001), "Variable Stars in Galactic Globular Clusters", The Astronomical Journal, 122 (5): 2587–2599, arXiv:astro-ph/0108024, Bibcode:2001AJ....122.2587C, doi:10.1086/323719, S2CID 38359010.
  1. On the southernmost line of the main (teapot) asterism; its declination means it will not rise (above the horizon) above the 58th parallel north and will need the observer to be as much as a further fifteen degrees of latitude south for detailed, little distorted observation
  2. on 31 August
  3. on 23 July
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