Nursery pictures: astronomers glimpse primordial clustering.Peering back to an era not long after the birth of the cosmos nearly 14 billion years ago, two teams of astronomers have captured the earliest snapshots yet of the emergence of galaxy clusters This page lists some of the more interesting galaxy clusters and groups. Defining the limits of galaxy clusters is imprecise as many clusters are still forming. In particular, clusters close to the Milky Way tend to be classified as galaxy clusters even when they are much smaller , one of the universe's basic motifs. "I'm just sort of blown away by this," comments Mare Davis of the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal . "If, 20 years ago, you said you were going to detect [galaxies at this distance], they wouldn't have believed you" The two research teams studied galaxies so distant that the light now arriving at telescopes reflects conditions of the galaxies at least 12.7 billion years ago. Rather than being evenly spread through space, these budding galaxies appear to be forming in groups, or protoclusters. That's consistent with a leading cosmological theory in which the earliest galaxies formed in the densest pockets of primordial material. One of the teams, led by Massimo Stiavelli of the Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). in Baltimore, Md., used the Hubble Space Telescope Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe. for its observations. The other, led by Masami Ouchi of the same institute, used the Subaru Telescope on Mauna Kea, Hawaii. These two studies, plus two others scrutinizing later stages in the early history of the universe, have refined the time line for the development of galaxy clusters. For example, Ouchi's team determined that the two protoclusters that it examined are forming stars at a prodigious rate. Meanwhile, images of a protocluster from an era about 2 billion years later reveal a considerable number of mature-looking galaxies that had already formed large populations of stars. A research team led by Charles C. Steidel of the California Institute of Technology California Institute of Technology, at Pasadena, Calif.; originally for men, became coeducational in 1970; founded 1891 as Throop Polytechnic Institute; called Throop College of Technology, 1913–20. in Pasadena, Calif., used the infrared Spitzer Space Telescope Spitzer Space Telescope: see infrared astronomy; observatory, orbiting. to make those observations. The Caltech group also found evidence that galaxies in protoclusters mature more quickly than do galaxies in open space, referred to as the field. They observed that the protocluster galaxies possessed bigger star populations than galaxies outside the protocluster and seemed to have formed their stars earlier. "The difference in galaxy properties is important," says Pieter van Dokkum of Yale University. "[It] suggests that the differences between field and cluster galaxies that we see today were already imprinted at an early time, when the clusters were still in the process of formation." A fourth team, led by Christopher R. Mullis of the University of Michigan (body, education) University of Michigan - A large cosmopolitan university in the Midwest USA. Over 50000 students are enrolled at the University of Michigan's three campuses. The students come from 50 states and over 100 foreign countries. at Ann Arbor, detected a seemingly mature cluster from 4.6 billion years after the Big Bang big bang Model of the origin of the universe, which holds that it emerged from a state of extremely high temperature and density in an explosive expansion 10 billion–15 billion years ago. . Its major period of star formation appears to be over. Mullis and his colleagues used the orbiting XMM-Newton X-ray Observatory and the Very Large Telescope The Very Large Telescope Project (VLT) is a system of four separate optical telescopes (the Antu telescope, the Kueyen telescope, the Melipal telescope, and the Yepun telescope) organized in an array formation. Each telescope has an 8.2 m aperture. in Atacama, Chile. They now are searching for more clusters from that ancient time period. Ouchi's team plans follow-up observations to investigate the history of star formation in the protoclusters it discovered. The researchers are examining how such protoclusters might have helped make the universe transparent by ionizing the opaque gas that previously permeated the universe. The Ouchi study appears in the Feb. 10 Astrophysical Journal Letters. The other reports will appear in future issues of the Astrophysical Journal. |
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