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Messier 68

Globular cluster in the constellation Hydra

Field	Value
name	Messier 68
image	[[Image:Messier 68 Hubble WikiSky.jpg	300px]]
caption	M68 from Hubble Space Telescope in 2008; 3.32 view
epoch	J2000
class	X
constellation	Hydra
ra
dec
dist_ly	33.6 kly
appmag_v	7.8
size_v	11.0
mass_msol
metal_fe	–2.23
radius_ly	53.5 ly
age	11.2 Gyr
notes	Relatively metal poor.
names	M68, NGC 4590, GCl 20

Note

the astronomical object

Messier 68 (also known as M68 or NGC 4590) is a globular cluster found in the east south-east of Hydra, away from its precisely equatorial part. It was discovered by Charles Messier in 1780. William Herschel described it as "a beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together". His son John 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. It is orbiting our galaxy's galactic bulge with a great eccentricity 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 through accretion from a satellite galaxy.

As of 2015, 50 variable stars have been identified in this cluster; the first 28 being identified as early as 1919–20 by American astronomer Harlow Shapley. 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

"Messier 68".
distance × sin( diameter_angle / 2 ) = 53.5 ly. radius
(December 2010). "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters". The Astronomical Journal.
"M 68".
(November 2011). "Young Radio Pulsars in Galactic Globular Clusters". The Astrophysical Journal.
(April 2008). "The correlation between blue straggler and binary fractions in the core of Galactic globular clusters". Astronomy and Astrophysics.

Info: Wikipedia Source

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globular-clusters hydra-(constellation) messier-objects ngc-objects astronomical-objects-discovered-in-1780 discoveries-by-charles-messier

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