# Messier 56

Messier 56
Messier 56 by Hubble Space Telescope. 3.6′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class X[1]
Constellation Lyra
Right ascension 19h 16m 35.57s[2]
Declination +30° 11′ 00.5″[2]
Distance 32.9 kly (10.1 kpc)[3]
Apparent magnitude (V) +8.3
Apparent dimensions (V) 8′.8
Physical characteristics
Mass 2.30×105[4] M
Metallicity ${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –2.00[6] dex
Estimated age 13.70 Gyr[6]
Other designations M56, NGC 6779, GCl 110, C 1914+300[7]
Messier 56 with amateur telescope
Map showing location of M56 (Roberto Mura)

Messier 56 (also known as M56 or NGC 6779) is a globular cluster in the constellation Lyra. It was discovered by Charles Messier on January 19, 1779. The cluster is located almost midway along an imaginary line between Albireo (β Cygni) and Sulafat (γ Lyrae). It is a challenge to find with large (50–80 mm) binoculars, appearing as a slightly fuzzy star.[8] The cluster can be resolved using a telescope with an aperture of 8 in (20 cm) or larger.[9]

M56 is at a distance of about 32,900[3] light-years from Earth and measures roughly 84 light-years across, with a combined mass some 230,000[4] times that of the Sun. It is about 31–32 kly (9.5–9.8 kpc) from the Galactic Center and 4.8 kly (1.5 kpc) above the galactic plane.[10] This cluster has an estimated age of 13.70 billion years and is following a retrograde orbit through the Milky Way. The properties of this cluster suggest that it may have been acquired during the merger of a dwarf galaxy, of which Omega Centauri forms the surviving nucleus. For Messier 56, the abundance of elements other than hydrogen and helium, what astronomers term the metallicity, has a very low value of [Fe/H] = –2.00 dex. This is equivalent to 1% of the abundance in the Sun.[6]

The brightest stars in M56 are of 13th magnitude, while it contains only about a dozen known variable stars, such as V6 (RV Tauri star; period: 90 days) or V1 (Cepheid: 1.510 days);[11] other variable stars are V2 (irregular) and V3 (semiregular). In 2000, a diffuse X-ray emission was tentatively identified coming from the vicinity of the cluster. This is most likely interstellar medium that has been heated by the passage of the cluster through the galactic halo. The relative velocity of the cluster is about 177 km s−1, which is sufficient to heat the medium in its wake to a temperature of 940,000 K.[12]

## 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. ^ a b Ivanov, Valentin D.; et al. (2000). "Near Infrared Photometry of Galactic Globular Clusters M56 and M15. Extending the Red Giant Branch vs. Metallicity Calibration Towards Metal Poor Systems". arXiv:astro-ph/0002118 [astro-ph].
4. ^ a b 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.
5. ^ distance × sin( diameter_angle / 2 ) = 42 ly. radius
6. ^ a b c 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. ^ "SIMBAD Astronomical Object Database". Results for NGC 6779. Retrieved 2006-11-16.
8. ^ Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated guide to astronomical wonders, DIY science, O'Reilly Media, Inc., p. 311, ISBN 0-596-52685-7
9. ^ Inglis, Mike (2004), Astronomy of the Milky Way: Observer's guide to the northern sky, Astronomy of the Milky Way 1, Springer, p. 90, ISBN 1-85233-709-5
10. ^ Bica, E.; et al. (April 2006), "Globular cluster system and Milky Way properties revisited", Astronomy and Astrophysics 450 (1): 105–115, arXiv:astro-ph/0511788, Bibcode:2006A&A...450..105B, doi:10.1051/0004-6361:20054351
11. ^ Pietrukowicz, P.; et al. (June 2008), "CURiuos Variables Experiment (CURVE): Variable Stars in the Metal-Poor Globular Cluster M56", Acta Astronomica 58: 121–130, arXiv:0806.1515, Bibcode:2008AcA....58..121P
12. ^ Hopwood, M. E. L.; et al. (July 2000), "A possible detection of diffuse extended X-ray emission in the environment of the globular cluster NGC 6779", Monthly Notices of the Royal Astronomical Society 316 (1): L5–L8, Bibcode:2000MNRAS.316L...5H, doi:10.1046/j.1365-8711.2000.03717.x