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M13 

History

M13 was discovered by Edmond Halley in 1714 and whose notes said: "This is but a little Patch, but it shews it self to the naked Eye, when the Sky is serene and the Moon absent." It was later catalogued by Charles Messier on June 1, 1764: "In the night of June 1 to 2, 1764, I have discovered a nebula in the girdle of Hercules, of which I am sure it doesn't contain any star; having examined it with a Newtonian telescope of four feet and a half, which magnified 60 times, it is round, beautiful & brilliant, the center brighter than the borders"

Characteristics

Hanging out in space at a distance of 25,100 light years, this 24 million year old beauty is one of the most impressive globular clusters for the northern hemisphere. Containing over a million stars packed into a 145 light year sphere, the center of this glorious object is 500x more concentrated than its outer perimeters. And out of all of those stars there stands one stranger,Barnard Number 29, which is a spectral type B2 – a young, blue star that was apparently collected on one of M13's journeys around our galaxy. However, radial velocity measurements have proved that it does belong to the globular cluster! When the Hubble Space Telescope was pointed towards this object they found 15 blue straggler star candidates. The stars in the blue horizontal branch of M13 appeared to be centrally depleted relative to other stellar types and the blue stragglers in the combined sample are centrally concentrated relative to the older red giant stars. However, the Stromgren photometry work done Frank Grundah (et al) suggests this is a normal occurrence in evolution. "We also note the existence of what appears to be two separate stellar populations on the horizontal branch of M13. Among other possibilities, it could arise as the result of differences in the extent to which deep mixing occurs in the precursor red giants."

Last Updated on Saturday, 14 August 2010 17:37