Messier 30

Messier 30 (also known as M30 or NGC 7099) is a globular cluster of stars in the southeast of the southern constellation of Capricornus, at about the declination of the sun when the latter is at December solstice.[lower-alpha 1] It was discovered by the French astronomer Charles Messier in 1764, who described it as a circular nebula without a star. In the New General Catalogue, compiled during the 1880s, it was described as a "remarkable globular, bright, large, slightly oval." It can be easily viewed with a pair of 10×50 binoculars,[9] forming a patch of hazy light some 4 arcminutes wide that is slightly elongated along the east–west axis.[9] With a larger instrument, individual stars can be resolved and the cluster will cover an angle of up to 12 arcminutes across graduating into a compressed core about one arcminute wide that has further star density within.[10]

Messier 30
Open cluster Messier 30 in Capricornus
Observation data (J2000 epoch)
ClassV[1]
ConstellationCapricornus
Right ascension21h 40m 22.12s[2]
Declination–23° 10′ 47.5″[2]
Distance27.14 ± 0.65 kly (8.3 ± 0.20 kpc)[3][4]
Apparent magnitude (V)+7.7[5]
Apparent dimensions (V)12'.0
Physical characteristics
Mass1.6×105[6] M☉
Metallicity = –2.27[7] dex
Estimated age12.93 Gyr[8]
Other designationsM30, NGC 7099, GCl 122[5]

It is longest observable (opposed to the sun) in the first half of August.[lower-alpha 2][9]

M30 is centered 27,100 light-years away from Earth with a roughly 2.5% margin of error,[4] and is about 93 light-years across.[10] The estimated age is roughly 12.9 billion years[8] and it forms a mass of about 160,000 times the mass of the Sun (M☉).[6] The cluster is following a retrograde orbit (against the general flow) through the inner galactic halo, suggesting that it was acquired from a satellite galaxy rather than forming within the Milky Way.[8] It is in this epoch 22.2 kly (6.8 kpc), from the center of the galaxy, compared to an estimated 26 kly (8.0 kpc) for the Sun.[11]

The cluster has passed through a dynamic process called core collapse and now has a concentration of mass at its core of about a million times the Sun's mass per cubic parsec. This makes it one of the highest density regions in the Milky Way galaxy. Stars in such close proximity will experience a high rate of interactions that can create binary star systems, as well as a type of star called a blue straggler that is formed by mass transfer.[3] A process of mass segregation may have caused the central region to gain a greater proportion of higher mass stars, creating a color gradient with increasing blueness toward the middle of the cluster.[12]

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.
  3. Lugger, Phyllis M.; et al. (March 2007), "Chandra X-Ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)", The Astrophysical Journal, 657 (1): 286–301, arXiv:astro-ph/0606382, Bibcode:2007ApJ...657..286L, doi:10.1086/507572
  4. Kains, N.; et al. (2016), "Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry", Astronomy and Astrophysics, 555 (1): 36–50, arXiv:1305.3606, Bibcode:2013A&A...555A..36K, doi:10.1051/0004-6361/201321819
  5. "M 30". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
  6. Vande Putte, D.; Cropper, Mark (January 2009), "Detecting the effect of globular cluster impacts on the disc of the Milky Way", Monthly Notices of the Royal Astronomical Society, 392 (1): 113–124, arXiv:0811.3106, Bibcode:2009MNRAS.392..113V, doi:10.1111/j.1365-2966.2008.14072.x
  7. 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.
  8. 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
  9. Bone, N. M. (August 2008), "Sky notes, 2008 August & September", Journal of the British Astronomical Association, 118 (4): 231–232, Bibcode:2008JBAA..118..231B
  10. O'Meara, Stephen James (1998), The Messier objects, Deep-sky companions, Cambridge University Press, p. 108, ISBN 978-0-521-55332-2
  11. Dinescu, Dana I.; et al. (January 1999), "Space Velocities of Southern Globular Clusters. II. New Results for 10 Clusters", The Astronomical Journal, 117 (1): 277–285, Bibcode:1999AJ....117..277D, doi:10.1086/300699
  12. Howell, Justin H.; Guhathakurta, Puragra; Tan, Amy (March 2000), "Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)", The Astronomical Journal, 119 (3): 1259–1267, arXiv:astro-ph/9912002, Bibcode:2000AJ....119.1259H, doi:10.1086/301270
  1. Thus, its northern limit for good visibility is a few degrees south of the Arctic Circle, all year
  2. This is when it is risen, throughout the night, so culminates about midnight. The earth's orbit means the sun leaves Capricornus, as if it heads east a few degrees NNE, on about 15 or 16th February, having figured in the constellation for a month.
Masp showing the location of M 30

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