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Messier 2
Messier 2 by Hubble Space Telescope; 2.5′ view
Observation data (J2000 epoch)
Class	II
Constellation	Aquarius
Right ascension	21 33 27.02
Declination	–00° 49′ 23.7″
Distance	55,000 ly (17 kpc)
Apparent magnitude (V)	6.5
Apparent dimensions (V)	16.0′
Physical characteristics
Mass	1.04×10 M☉
Radius	87.3 ly
Metallicity	${\displaystyle {\begin{smallmatrix}\left\end{smallmatrix}}}$ = –1.65 dex
Estimated age	12.5 Gyr
Other designations	NGC 7089
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 while observing a comet with Jacques Cassini. 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.

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 are of apparent magnitude 6.5.

Characteristics

M2 is about 55,000 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.

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. M2 is part of the Gaia Sausage, the hypothesized remains of a merged dwarf galaxy.

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.

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.

Oosterhoff Classification

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, and an average RRab Lyrae pulsation period around .64 days indicates a type II cluster. 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.

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.

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. S2CID 119183070.
3. Helmi, A; van Leeuwen, F; McMillan, P J; Massari, D; Antoja, T; Robin, A; Lindegren, L; Bastian, U (2018). "Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way". Astronomy and Astrophysics. 616. Gaia Collaboration: A12. arXiv:1804.09381. Bibcode:2018A&A...616A..12G. doi:10.1051/0004-6361/201832698. S2CID 260496632.
4. "Messier 2". SEDS Messier Catalog. Retrieved 21 July 2024.
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. S2CID 118649860.
6. distance × sin( diameter_angle / 2 ) = 87.3 ly. radius
7. ^ 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. ^ "M 2". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.
9. 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. "THE GLOBULAR CLUSTER M2 – Astronomy Magazine – Interactive Star Charts, Planets, Meteors, Comets, Telescopes". cs.astronomy.com. Retrieved 2023-04-29.
11. admin (2015-01-17). "Messier 2". Messier Objects. Retrieved 2023-04-29.
12. ^ 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.
13. 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.
14. "M2, NGC 7089". noirlab.edu. Retrieved 2023-04-29.
15. 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.
16. 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.
17. 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 .

See also

• List of Messier objects

External links

• M2,SEDS Messier pages
• M2, Galactic Globular Clusters Database page
• Messier 2 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

• Astronomy
• Stars
• Outer space

v t e Messier objects
List	M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15 M16 M17 M18 M19 M20 M21 M22 M23 M24 M25 M26 M27 M28 M29 M30 M31 M32 M33 M34 M35 M36 M37 M38 M39 M40 M41 M42 M43 M44 M45 M46 M47 M48 M49 M50 M51 M52 M53 M54 M55 M56 M57 M58 M59 M60 M61 M62 M63 M64 M65 M66 M67 M68 M69 M70 M71 M72 M73 M74 M75 M76 M77 M78 M79 M80 M81 M82 M83 M84 M85 M86 M87 M88 M89 M90 M91 M92 M93 M94 M95 M96 M97 M98 M99 M100 M101 M102 M103 Added M104 M105 M106 M107 M108 M109 M110
See also	Caldwell catalogue Catalogue of Nebulae and Clusters of Stars Herschel 400 Catalogue Index Catalogue New General Catalogue Revised New General Catalogue
Category Commons Portal

v t e Constellation of Aquarius
Aquarius in Chinese astronomy Aquarius Stream List of stars in Aquarius
Stars	Bayer α (Sadalmelik) β (Sadalsuud) γ (Sadachbia) δ (Skat) ε (Albali) ζ η θ (Ancha) ι κ (Situla) λ (Hydor) μ ν ξ (Bunda) ο π ρ σ τ τ υ φ χ ψ (91) ψ ψ ω ω A A b b b c c c d e f g g h i i i k α PsA C Flamsteed 1 4 5 7 8 9 10 11 12 14 15 16 17 18 19 20 21 24 26 28 29 30 32 35 36 37 39 40 41 42 44 45 47 49 50 51 54 56 58 60 61 64 65 67 70 72 74 75 77 78 81 82 84 85 87 94 96 97 100 Variable R U AE DV EP EW EZ FO HK IL HU IZ LP HR 8017 8056 8121 8263 8363 8453 8500 8507 8581 8612 8629 8645 8716 8783 8836 8856 8879 8924 9014 HD 206610 (Bosona) 210277 212771 (Lionrock) 215152 219617 220466 220689 222093 222582 Other 2MASS J21392676+0220226 BD−22 5866 Gliese 849 K2-21 K2-28 K2-58 K2-72 K2-138 LS IV-14 116 Sneden's Star TRAPPIST-1 WASP-6 (Márohu) WASP-47 WASP-69 WASP-75
Exoplanets ψ Aquarii b Gliese 849 b Gliese 876 b c d e HD 206610 b HD 210277 b HD 212771 b (Victoriapeak) HD 221416 b HD 222582 b K2-66b K2-72b c d e K2-138b TRAPPIST-1b c d e f g h WASP-6b
Star clusters Messier 2 Messier 72 Messier 73
Nebulae Helix Nebula Saturn Nebula
Galaxies	NGC 6975 7001 7010 7047 7051 7065 7069 7077 7081 7184 7222 7252 7257 7301 7302 7393 7492 7585 7592 7600 7606 7723 7727 7759 Other Aquarius Dwarf ESO 603-G21 Lyman-alpha blob 1 PGC 1228197 PHL 293B SMM J2135-0102 WISE J224607.57−052635.0 J2345-0449
Galaxy clusters Abell 2597 RXC J2211.7-0350 XMMXCS 2215-1738
Astronomical events SN 2213-1745
Category

• Globular clusters
• NGC objects
• Messier objects
• Gaia-Enceladus
• Aquarius (constellation)
• Astronomical objects discovered in 1746