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Object description
The large globular cluster NGC 6397 in the constellation Ara

Short objekt description:

NGC 6397 is an ancient stellar jewel box and an often overlooked and relatively unknown globular cluster in the constellation Ara (Altar). Yet, with an apparent diameter of over 30 arcminutes and a magnitude 5.3 brightness, it is a very prominent object in the southern night sky.

The brightest stars have a magnitude 10 brightness. It is classified as type IX. At a distance of only 7,800 light years, it is the second closest globular cluster to the Solar System - after Messier 4 in the constellation of Scorpio - and has therefore been studied in many scientific publications. During one of these investigations, an elliptical galaxy about 1 billion light years away was found by chance between the stars of NGC 6397, which in turn is surrounded by a swarm of about 200 globular clusters. This is the most distant known cluster of globular clusters to date.

The central region of the cluster is extremely dense (core collapse). It contains about 400,000 stars and the stars are - according to a study with the Hubble Space Telescope - about 13.5 billion years old. Recent studies with the Hubble telescope suggest that there may be several stellar black holes at the centre of the globular cluster. NGC 6397 was discovered in 1751 by the French astronomer Nicolas Louis de Lacaille.

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