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The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. [4] [5] [6] The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, [7] then finally as a globular cluster in the early 19th century ...
Core collapse can refer to: The collapse of the stellar core of a massive star, such as the core collapse that produces a supernova; Core collapse (cluster), the dynamic process that leads to a concentration of stars at the core of a globular cluster
NGC 6752 (also known as Caldwell 93 and nicknamed the Great Peacock Globular [7]) is a globular cluster in the constellation Pavo. [8] It is the fourth-brightest globular cluster in the sky, after Omega Centauri, 47 Tucanae and Messier 22, respectively. It is best seen from June to October in the Southern Hemisphere. [9]
NGC 6397 (also known as Caldwell 86) is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752. [9] It is located about 7,800 light-years from Earth, [3] making it one of the two nearest globular clusters to Earth (the other one being Messier 4).
The cluster does not display the normal indications of core collapse, but evidence suggests it may have instead passed through a post core-collapse bounce state within the past two billion years. The central luminosity density is 2.22 L ☉ ·pc −3, which is low for a globular cluster. [8]
It is considered a metal-poor inner halo cluster, being the third most metal-poor globular cluster within 9.8 kly (3 kpc) of the center. [8] The cluster has 5.72 × 10 5 times the mass of the Sun. [5] It is estimated to be around 12.9 billion years old, [6] and is believed to have undergone core collapse. [8]
NGC 6355 is a globular cluster located in the constellation Ophiuchus. [5] It is at a distance of 28,000 light years away from Earth, and is currently part of the Galactic bulge. [3] NGC was discovered by the German-born British astronomer William Herschel on 24 May 1784. [6]
NGC 6522 is possibly the oldest star cluster in the Milky Way, [10] with an age of more than 12 billion years. [11] [12] It is a core collapsed cluster with a core radius of 0.5′ and a 1.0′ half-light radius. [9] The cluster formed four billion years before the Milky Way galactic bar appeared, and may have been confined to the bar for a ...