Messier 2

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Messier 2
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Messier 2 by Hubble Space Telescope; 2.5Template:Prime view
Observation data (J2000 epoch)
ClassII[1]
ConstellationAquarius
Right ascensionTemplate:RA[2]
DeclinationTemplate:DEC[2]
Distance38,140 ly (11.693 kpc)[3]
Apparent magnitude (V)6.5[4]
Apparent dimensions (V)16.0Template:Prime
Physical characteristics
Mass1.04×105[5] M☉
Radius87.3 ly[6]
Metallicity[Fe/H] = –1.65[5] dex
Estimated age12.5 Gyr[7]
Other designationsNGC 7089[8]
See also: Globular cluster, List of globular clusters

Messier 2 or M2 (also designated NGC 7089) is a globular cluster in the constellation Aquarius, five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746, and is one of the largest known globular clusters.

Discovery and visibility

M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746[9] while observing a comet with Jacques Cassini.[10] Charles Messier rediscovered it in 1760, but thought that it is a nebula without any stars associated with it. William Herschel, in 1783, was the first to resolve individual stars in the cluster.[11]

M2 is, under extremely good conditions, just visible to the naked eye. Binoculars or a small telescope will identify this cluster as non-stellar, while larger telescopes will resolve individual stars, of which the brightest is of apparent magnitude 12.[12]

Characteristics

File:M2map.png
Chart showing location of M2

M2 is about 37,500 light-years distant from Earth. At 175 light-years in diameter, it is one of the larger globular clusters known. The cluster is rich, compact, and significantly elliptical. It is 12.5 billion years old and one of the older globular clusters associated with the Milky Way galaxy.[7]

M2 contains about 150,000 stars, including 21 known variable stars. Its brightest stars are red and yellow giant stars. The overall spectral type is F4.[8] M2 is part of the Gaia Sausage, the hypothesized remains of a merged dwarf galaxy.[13]

Data from Gaia has led to the discovery of an extended tidal stellar stream, about 45 degrees long and 300 light-years (100 pc) wide, that is likely associated with M2. It was possibly perturbed due to the presence of the Large Magellanic Cloud.[14]

Messier 2 is located within our Milky Way galaxy, and is one of the oldest clusters of stars designated to the Milky Way. Like most globular clusters, M2 is found within the galactic halo, specifically in the southern galactic cap. This places it right below the southern pole of the Milky Way.[15]

Oosterhoff classification

File:Curva RRab.png
Light curve of an RRab variable star

M2 is defined as an Oosterhoff type II globular cluster. Oosterhoff type is a classification system of globular clusters originally observed by Pieter Oosterhoff in where globular clusters are generally separated into two types. Oosterhoff type is determined by metallicity, age, and average pulsation period of type ab RR Lyrae variable stars of the cluster. A cluster metallicity below −1.6, an age above 13 billion years,[16] and an average RRab Lyrae pulsation period around .64 days indicates a type II cluster.[17] This .64 day value, coupled with a metallicity of −1.65, provides evidence that M2 follows the Oosterhoff Gap phenomena. This is an observed gap in the grouping of type I and type II clusters in the Milky Way on a metallicity vs average RRab pulsation period plot.[18]

M2 is a bit of an anomaly in reference to Oosterhoff type. While it satisfies the metallicity and RRab Lyrae pulsation period conditions, it actually has an age of 12.5 Gyr, well below the cutoff age of 13 Gyr normal for a Oosterhoff type II cluster. This is unexpected because age of a cluster is generally determined from metallicity. However, this abnormality is explained in an article by Marín-Franch.[7] Nevertheless, in a recent study, Botev et al. proposed a new lower limit of 13.2 Gyr for the age of M2.[19]

References

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  1. ^ Page Module:Citation/CS1/styles.css has no content.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 Page Module:Citation/CS1/styles.css has no content.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. ^ Page Module:Citation/CS1/styles.css has no content.Baumgardt, H.; Vasiliev, E. (2021). "Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data". Monthly Notices of the Royal Astronomical Society. 505 (4): 5957. arXiv:2105.09526. Bibcode:2021MNRAS.505.5957B. doi:10.1093/mnras/stab1474.
  4. ^ Page Module:Citation/CS1/styles.css has no content."Messier 2". SEDS Messier Catalog. Retrieved 21 July 2024.
  5. ^ a b Page Module:Citation/CS1/styles.css has no content.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.
  6. ^ distance × sin( diameter_angle / 2 ) = 87.3 ly. radius
  7. ^ a b c Page Module:Citation/CS1/styles.css has no content.Marín-Franch, Antonio; Aparicio, Antonio; Piotto, Giampaolo; Rosenberg, Alfred; Chaboyer, Brian; Sarajedini, Ata; Siegel, Michael; Anderson, Jay; Bedin, Luigi R.; Dotter, Aaron; Hempel, Maren; King, Ivan; Majewski, Steven; Milone, Antonino P.; Paust, Nathaniel; Reid, I. Neill (2009). "The ACS Survey of Galactic Globular Clusters. VII. Relative Ages". The Astrophysical Journal. 694 (2): 1498. arXiv:0812.4541. Bibcode:2009ApJ...694.1498M. doi:10.1088/0004-637X/694/2/1498. S2CID 118407466.
  8. ^ a b Page Module:Citation/CS1/styles.css has no content."M 2". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15. {{cite web}}: Invalid |mode=Script error: No such module "Citation mode". (help)
  9. ^ Page Module:Citation/CS1/styles.css has no content.Stephen James O'Meara (7 April 2014). Deep-Sky Companions: The Messier Objects. Cambridge University Press. pp. 47–. ISBN 978-1-107-01837-2.
  10. ^ Page Module:Citation/CS1/styles.css has no content."THE GLOBULAR CLUSTER M2 – Astronomy Magazine – Interactive Star Charts, Planets, Meteors, Comets, Telescopes". cs.astronomy.com. Retrieved 2023-04-29.
  11. ^ Page Module:Citation/CS1/styles.css has no content.admin (2015-01-17). "Messier 2". Messier Objects. Retrieved 2023-04-29.
  12. ^ Page Module:Citation/CS1/styles.css has no content.Cudworth, Kyle M.; Rauscher, Bernard J. (1987). "Astrometry and Photometry in the Globular Cluster System M2". The Astronomical Journal. 93: 856. Bibcode:1987AJ.....93..856C. doi:10.1086/114369.
  13. ^ Page Module:Citation/CS1/styles.css has no content.Myeong, G. C; Evans, N. W; Belokurov, V; Sanders, J. L; Koposov, S. E (2018). "The Sausage Globular Clusters". The Astrophysical Journal. 863 (2): L28. arXiv:1805.00453. Bibcode:2018ApJ...863L..28M. doi:10.3847/2041-8213/aad7f7. S2CID 67791285.
  14. ^ Page Module:Citation/CS1/styles.css has no content.Grillmair, Carl J. (2022). "The Extended Tidal Tails of NGC 7089 (M2)". The Astrophysical Journal. 929 (1): 89. arXiv:2203.04425. Bibcode:2022ApJ...929...89G. doi:10.3847/1538-4357/ac5bd7. S2CID 247318732.
  15. ^ Page Module:Citation/CS1/styles.css has no content."M2, NGC 7089". noirlab.edu. Retrieved 2023-04-29.
  16. ^ Page Module:Citation/CS1/styles.css has no content.van den Bergh, Sidney (2011). "Some Systematics of Galactic Globular Clusters". Publications of the Astronomical Society of the Pacific. 123 (907): 1044–1053. arXiv:1108.0708. Bibcode:2011PASP..123.1044V. doi:10.1086/662132. ISSN 0004-6280.
  17. ^ Page Module:Citation/CS1/styles.css has no content.Stobie, R. S. (1971). "On the Difference Between the Oosterhoff Types i and II Globular Clusters". The Astrophysical Journal. 168: 381. Bibcode:1971ApJ...168..381S. doi:10.1086/151094.
  18. ^ Page Module:Citation/CS1/styles.css has no content.Kuehn, Charles A.; Smith, Horace A.; Catelan, Marcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Dame, Kyra; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura (2013-10-01). "RR Lyrae in the LMC: Insights Into the Oosterhoff Phenomenon". arXiv:1310.0553 [astro-ph.SR].
  19. ^ Page Module:Citation/CS1/styles.css has no content.Botev, Svetoslav; Petrov, Georgi; Valcheva, Antoniya; Nedialkov, Petko (2025-07-01). "Structural parameters of the globular cluster M 2 determined by ellipse fitting of its stellar density". Physica Scripta. 100 (7): 075005. Bibcode:2025PhyS..100g5005B. doi:10.1088/1402-4896/add843. ISSN 0031-8949.

See also

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