NGC 6539

NGC 6539, or GCL 85, is a globular cluster of stars in the constellation Serpens. It was discovered by Danish astronomer Theodor Brorsen in 1856. This cluster is visible with a small amateur telescope, having an apparent visual magnitude of 9.6 and an angular size of . It is located at a distance of 8.165 kpc from the Sun, and 3.1 kpc from the Galactic Center.

This cluster is located in the outer parts of the Galactic bulge. There is a large dark cloud complex located in the fore of this cluster, causing reddening from extinction. NGC 6539 has a core radius of , a half-mass radius of , and a tidal radius of . Compared to other globular clusters, NGC 6539 is considered metal rich, indicating that it has a relatively higher abundance of elements more massive than helium. Thirteen variable stars have been detected within of the core, of which a dozen are long period variables. A millisecond pulsar was discovered in 1990.

References

| display-authors=1 | journal=The Astrophysical Journal

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| archive-url=https://web.archive.org/web/20060928091522/http://www.kopernik.org/images/archive/n6539.htm | access-date=2006-09-28 | archive-date=2006-09-28 }}

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| display-authors=1 | journal=The Astronomical Journal

| editor-last=Green | editor-first=D. W. E.