Messier 30

Messier 30
Messier 30
	Open cluster Messier 30 in Capricornus
Observation data (J2000 epoch)
Class	V
Constellation	Capricornus
Right ascension	21h 40m 22.12s
Declination	–23° 10′ 47.5″
Distance	27.14 ± 0.65 kly (8.3 ± 0.20 kpc)
Apparent magnitude (V)	7.2
Apparent dimensions (V)	12'.0
Physical characteristics
Mass	1.6×105 M☉
Metallicity	= –2.27 dex
Estimated age	12.93 Gyr
Other designations	M30, NGC 7099, GCl 122
	See also: Globular cluster, List of globular clusters

Messier 30 (also known as M30, NGC 7099, or the Jellyfish Cluster) 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.^[a] 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,^[10] forming a patch of hazy light some 4 arcminutes wide that is slightly elongated along the east–west axis.^[10] 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.^[11]

It is longest observable (opposed to the Sun) in the first half of August.^[b]^[10]

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.^[11] 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.^[12]

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.^[13]

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[5] "Messier 30". SEDS Messier Catalog. Archived from the original on 30 March 2023. Retrieved 28 April 2022.

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