Messier 68
Messier 68 is a globular cluster in the equatorial constellation Hydra. 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 at a distance of about 33,000 light-years away from Earth and is orbiting through the Milky Way with a large eccentricity of 0.5. This orbit carries it as far as 100,000 light years from the galactic 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 by the Milky Way galaxy through accretion from a satellite galaxy.
All told, as of 2015 a total of 50 variable stars have been identified in this cluster; the first 28 being identified as early as 1919–1920 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.
