jetpacksunrise:Top: The distant Coma Cluster of galaxies is home to the ghostly spiral NGC 4921, who
jetpacksunrise:Top: The distant Coma Cluster of galaxies is home to the ghostly spiral NGC 4921, whose precise distance from Earth has been the subject of intense inquiry. Astronomers hope that by combining their knowledge of its recession speed and its distance, they will get a better measure of how fast the universe is expanding. The search for Cepheid stars in NGC 4921 has yielded beautifully detailed images, where ancient background galaxies, some of the earliest in the universe, whirl like motes of dust.Bottom: At the time when the Hercules Cluster looked as we see it, the most complex form of life on Earth was the trilobite. At its center, two spiral galaxies are colliding, a process that astronomers suspect produces cloud-like elliptical galaxies. Part of a supercluster of galaxies, Hercules lies in a region of space where superclusters themselves have formed into great walls of galaxies, the very largest structures in the known universe. -- source link