Messier 68 (also known as M68 or NGC 4590) is a
globular cluster
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...
found in the east south-east of
Hydra, away from its precisely
equatorial Equatorial may refer to something related to:
*Earth's equator
**the tropics, the Earth's equatorial region
**tropical climate
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** equatorial orbit
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* equatorial ...
part. It was discovered by
Charles Messier
Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects''. Messier's purpose ...
in 1780.
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...
described it as "a beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together". His son
John
John is a common English name and surname:
* John (given name)
* John (surname)
John may also refer to:
New Testament
Works
* Gospel of John, a title often shortened to John
* First Epistle of John, often shortened to 1 John
* Secon ...
noted that it was "all clearly resolved into stars of 12th magnitude, very loose and ragged at the borders".
[
M68 is centred about 33,600 light-years away from ]Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
. It is orbiting our galaxy's galactic bulge
In astronomy, a galactic bulge (or simply bulge) is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see galactic spheroid). Bulges ...
with a great eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
of 0.5. This takes it to 100,000 light years from the center.[ It is one of the most metal-poor globular clusters, which means it has a paucity of elements other than hydrogen and helium. The cluster may be undergoing core-collapse, and it displays signs of being in rotation. The cluster may have been acquired in its gravitational tie to the ]Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
through accretion from a satellite galaxy.[
As of 2015, 50 ]variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...
s have been identified in this cluster; the first 28 being identified as early as 1919–20 by American astronomer Harlow Shapley
Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal.
Shapley used Cepheid variable stars to estim ...
. Most of the variables are of type RR Lyrae
RR Lyrae is a variable star in the Lyra constellation, figuring in its west near to Cygnus. As the brightest star in its class, it became the eponym for the RR Lyrae variable class of stars and it has been extensively studied by astro ...
, or periodic variables. Six of the variables are of the SX Phoenicis
SX Phoenicis is a variable star in the southern constellation Phoenix. With an apparent visual magnitude ranging around 7.33, it is too faint to be readily seen with the naked eye and requires binoculars. It is located 272 light yea ...
variety, which display short pulsating behavior.[
]
Gallery
File:A_Ten_Billion_Year_Stellar_Dance.jpg, A 2012 view of M68 from the Wide Field Camera of Hubble's Advanced Camera for Surveys
See also
* List of Messier objects
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters'').
Because Messier was only in ...
References
External links
*
Globular Cluster M68 @ SEDS Messier pages
Messier 68, Galactic Globular Clusters Database page
*
{{DEFAULTSORT:Messier 068
Globular clusters
Hydra (constellation)
068
NGC objects
Astronomical objects discovered in 1780