# Messier 5

Messier 5
Globular cluster Messier 5 in Serpens
Observation data (J2000 epoch)
ClassV[1]
ConstellationSerpens
Right ascension15h 18m 33.22s[2]
Declination+02° 04′ 51.7″[2]
Distance24.5 kly (7.5 kpc)[3]
Apparent magnitude (V)5.6[4]
Apparent dimensions (V)23′.0
Physical characteristics
Mass8.57×105[5] M
Metallicity${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.12[6] dex
Estimated age10.62 Gyr[6]
Other designationsNGC 5904, GCl 34[7]

Messier 5 or M5 (also designated NGC 5904) is a globular cluster in the constellation Serpens. It was discovered by Gottfried Kirch in 1702.

## Discovery and visibility

M5 is, under extremely good conditions, just visible to the naked eye as a faint "star" 0.37 of a degree (22' (arcmin)) north-west of star 5 Serpentis. Binoculars and/or small telescopes resolve the object as non-stellar; larger telescopes will show some individual stars, some of which are as bright as apparent magnitude 10.6.[8] M5 was discovered by German astronomer Gottfried Kirch in 1702 when he was observing a comet. Charles Messier noted it in 1764 and—a studier of comets—cast it as one of his nebulae. William Herschel was the first to resolve individual stars in the cluster in 1791, counting roughly 200.[9] Messier 5 is receding from the Solar System at a speed over 50 km/s.[10]

## Notable features

One hundred and five stars in M5 are known to be variable in brightness, 97 of them belonging to the RR Lyrae type.[11] RR Lyrae stars, sometimes referred to as "Cluster Variables", are somewhat similar to Cepheid type variables and as such can be used as a tool to measure distances in outer space since the relation between their luminosities and periods are well known. The brightest and most easily observed variable in M5 varies from magnitude 10.6 to 12.1 in a period of just under 26.5 days.[8]

The cluster contains two millisecond pulsars, one of which is in a binary, allowing the proper motion of the cluster to be measured. The binary could help our understanding of neutron degenerate matter; the current median mass, if confirmed, would exclude any "soft" equation of state for such matter.[12] The cluster has been used to test for magnetic dipole moments in neutrinos, which could shed light on some hypothetical particles such as the axion.[13]

A dwarf nova has also been observed in this cluster.[14]

Messier 5 by Hubble Space Telescope - 2.85′ view

## 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. ^ a b 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. ^ Paust, Nathaniel E. Q.; et al. (February 2010), "The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions", The Astronomical Journal, 139 (2): 476–491, Bibcode:2010AJ....139..476P, doi:10.1088/0004-6256/139/2/476, hdl:2152/34371.
4. ^ "Messier 5". SEDS Messier Catalog. Retrieved 27 April 2022.
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. ^ a b 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.
7. ^ "M 5". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.
8. ^ a b Coutts Clement, Christine M.; Sawyer Hogg, Helen (August 1977). "The Bright Variable Stars in Messier 5". Journal of the Royal Astronomical Society of Canada. 71: 281. Retrieved 1 March 2021.
9. ^ "William Herschel's Observations of the Messier Objects". www.messier.seds.org. Students for the Exploration and Development of Space. Retrieved 1 March 2021.
10. ^ Harris, William E. (1996). "A Catalog of Parameters for Globular Clusters in the Milky Way". The Astronomical Journal. 112: 1487. Bibcode:1996AJ....112.1487H. doi:10.1086/118116.
11. ^ Szeidl, B.; Hurta, Zs.; Jurcsik, J.; Clement, C.; Lovas, M. (2011). "Long-term photometric monitoring of Messier 5 variables - I. Period changes of RR Lyrae stars". Monthly Notices of the Royal Astronomical Society. 411 (3): 1744–1762. arXiv:1010.1115. Bibcode:2011MNRAS.411.1744S. doi:10.1111/j.1365-2966.2010.17815.x. S2CID 118519067.
12. ^ Freire, P. C. C.; Wolszczan, A.; van den Berg, M.; Hessels, J. W. T. (2008). "A Massive Neutron Star in the Globular Cluster M5". The Astrophysical Journal. 679 (2): 1433–1442. arXiv:0712.3826. Bibcode:2008ApJ...679.1433F. doi:10.1086/587832. S2CID 118743395.
13. ^ Viaux, N.; Catelan, M.; Stetson, P. B.; Raffelt, G. G.; Redondo, J.; Valcarce, A. A. R.; Weiss, A. (2013). "Particle-physics constraints from the globular cluster M5: Neutrino dipole moments". Astronomy & Astrophysics. 558: A12. arXiv:1308.4627. Bibcode:2013A&A...558A..12V. doi:10.1051/0004-6361/201322004. S2CID 59056210.
14. ^ Neill, James D.; Shara, Michael M.; Caulet, Adeline; Buckley, David A.H. (June 2002). "The first orbital period for a dwarf nova in a globular cluster: V101 in M5". The Astronomical Journal. 123 (6): 3298–3304. doi:10.1086/340469. Retrieved 1 March 2021.