Messier 68 (also known as M68 or NGC 4590) is a

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

found in the east south-east of Hydra, away from its precisely 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'', referred to with th ...

in 1780.

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

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 * Second E ...

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-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. 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 group of stars found near the center of most spiral galaxies (see ''galactic spheroid'' ...

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 or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

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 systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

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 astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid var ...

. Most of the variables are of type RR Lyrae, or periodic variables. Six of the variables are of the SX Phoenicis 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 File:Radio cluster.png, NGC 4590 imaged using CTIO's PROMPT-6 telescope. The RGB filters were used, 10 second exposure on each. Additionally, a layer of WISE 12 micron data from SkyViewer was layered on top.

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 Discoveries by Charles Messier

Gallery

See also

References

External links