Globular Star Cluster M5                                           

Taken June 18, 2005 @ Cold Spring Observatory    Image Credit: Fred Calvert / Cold Spring Observatory

Globular cluster M5 (NGC 5904) is one of the largest, 130 light years across - and oldest star cluster, around 13 billion years old. Under good seeing conditions the cluster can be seen with the naked eye. The cluster is located in the constellation Sepens at a distance of around 25,000 light years from Earth.

It's estimated that there is around 250,000 star in the cluster.

Globular cluster M5 was first seen by Gottfried Kirch and his wife Maria Margarethe on May 5, 1702, when they observed a comet, and described as a "nebulous star". Charles Messier found it independently on May 23, 1764, and described it as a round nebula which "doesn't contain any stars". William Herschel was the first to resolve this cluster into stars; he counted 200 of them with his 40-foot [FL] reflector in 1791, "although the middle is so compressed that it is impossible to distinguish the components."

M5 contains the considerably large number of 105 known variable stars. The first variables in this cluster were noted by A.A. Common in 1890. S.I. Bailey (1899) found 85 short-period variables in this cluster, of type RR Lyrae (or cluster variables); 97 of them were known in 1955, according to Kenneth Glyn Jones. One of the other variables is a dwarf nova, according to Cecilia Payne-Gaposhkin (she also mentions two more dwarf novae in the globulars M30 and NGC 6712).

Reference:

S.I. Bailey (1899). The Periods of the Variable Stars in the Cluster Messier 5. Astrophysical Journal, Vol. 10, pp. 255-65. [ADS: 1899ApJ....10..255B]

What are the Blue Stars About?

Most Globular Cluster like M5 contain very old stars that are red. Below is an explanation about the Blue Stars called Blue Stragglers.

Blue stragglers are stars in open or globular clusters that are hotter and bluer than other cluster stars having the same luminosity. Thus, they are separate from other stars on the cluster's Hertzsprung-Russell diagram. Blue straggler stars appear to violate standard theories of stellar evolution, in which all stars born at the same time should lie on a clearly defined curve in the Hertzsprung-Russell diagram, with their positions on that curve determined solely by their initial mass. Since blue stragglers often lie well off this curve, they may undergo abnormal stellar evolution.

The cause of this is not yet clearly known, but the leading hypothesis is that they are current or former binary stars that are in the process of  merging or have already done so. The merger of two stars would create a single star with larger mass, making it hotter and more luminous than stars of a similar age. If this theory is correct, then blue stragglers would no longer cause a problem for stellar evolution theory; the resulting star would have more hydrogen in its core making it behave like a much younger star. There is evidence in favor of this view, notably that blue straggler stars appear to be much more common in dense regions of clusters, especiall in the cores of globular clusters. Since there are more stars per unit volume, collisions and close-encounters are far more likely in clusters than among field stars.
       

      Diagram Credit: STScl

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Equipment:  Meade LX200 Telescope @ f10.0 / SBIG ST2000XM /CFW8 Color Filter Wheel /AO-7 Adaptive Optics Unit

Exposure Data: LRGB

Luminance = 30 minutes  binned 1 X 1 / Red = 15 minutes binned 1 X 1 / Green = 15 minutes binned 1 X 1 /  Blue = 15 minutes binned 1 X 1

             LX 200 Telescope                           SBIG ST2000XM / CFW8 / A07                                 Cold Spring Observatory Control Room

Stellar Spectral Types :

Stars are classified by their spectra (the elements that they absorb) and their temperature. There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M.

O and B stars are uncommon but very bright; M stars are common but dim.

Type "O" & "B" type stars have very short  life cycles, only about one million years compared to a "G" type star (like our sun) who life cycle is around 9 billion years.

By the way, not to worry, were only about 4.5 billion years into our sun's life, with 4.5 billion years, give or take a few billion to go.

Plenty of time to do everything in life you ever wanted to do.

The commonly used mnemonic for the sequence of these classifications is "Oh Be A Fine Girl, Kiss Me".

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