HYDRA CLUSTER, or Abell 1060, galaxy cluster containing approximately 157 bright galaxies in the Hydra constellation. The cluster is notable for its large size, spanning roughly 10 million light-years and containing an unusually high proportion of dark matter. At more than 100 million light-years from Earth, Hydra is one of just three galaxy clusters within 200 million light-years of the Milky Way; its neighbors the Virgo Cluster and the Centaurus Cluster are 65 million light-years and 150 million light-years away from Earth, respectively. The Hydra Cluster comprises three dominant galaxies at its heart: the ellipticals NGC 3309 and NGC 3311 and the spiral galaxy NGC 3312. Each has a diameter of about 150,000 light-years. The two elliptical galaxies are situated relatively close to each other but show no obvious signs of interaction.
Galaxy clusters are the largest gravitationally bound objects in the universe, typically comprising hundreds if not thousands of galaxies. And yet the galaxies themselves represent no more than five percent of a cluster’s total mass, roughly eighty percent of which is made up of dark matter (the rest being mostly plasma). The gravitational force exerted by dark matter within these clusters acts directly on the path of light, bending it. This resulting “gravitational lensing” effectively magnifies the clusters, rendering the galaxies within them observable from Earth despite the immense distances involved.
In a cluster, hot plasma typically fills the space between galaxies. The plasma has an illuminating effect on clusters because it shines brightly under X-ray light and also acts on radio light shining through the clusters, even when it comes from a distant source. Supermassive black holes within individual galaxies exert influence over the entire cluster, adding to the intricate dynamics of these cosmic behemoths.
In Greek mythology the Hydra is a many-headed water serpent slain by Hercules. The Hydra constellation, the largest of the eighty-eight constellations in the night sky, was named for its serpent-like appearance.