X-ray satellites discover the biggest collisions in the UniverseJuly 18, 2007The orbiting X-ray telescopes XXM-Newton and Chandra have caught a pair of galaxy clusters merging into a giant cluster. The discovery adds to existing evidence that galaxy clusters can collide faster than previously thought. When individual galaxies collide and spiral into one another, they discard trails of hot gas that stretch across space, providing signposts to the mayhem. Recognising the signs of collisions between whole clusters of galaxies, however, is not as easy. Undaunted, Renato Dupke and colleagues from the University of Michigan, Ann Arbor, have used ESA's XMM-Newton and NASA's Chandra orbiting X-ray observatories, to disentangle the puzzling galaxy cluster, Abell 576. Previous X-ray observations had hinted that the gas was not moving uniformly across the cluster. Using the superior sensitivity and spectral resolution of XMM-Newton and Chandra's high spatial resolution, Dupke took readings from two locations in the cluster and saw that there was a distinct difference in the velocity of the gas. One part of the cluster seemed to be moving away from us faster than the other. The puzzle was that the moving gas itself was cold by astronomical standards. If this gas moved at such high speeds, it should have had a temperature of more than double the measured 50 million degrees Celsius. "The only explanation was to take the Bullet Cluster and turn it in the line of sight, such that one galaxy cluster is directly behind the other" says Dupke. The Bullet Cluster is a much-studied pair of galaxy clusters, which have collided head on. One has passed through the other, like a bullet travelling through an apple. In the Bullet Cluster, this is happening across our line of sight, so we can clearly see the two clusters. Dupke realised that Abell 576 is also a collision, but seen head on, so one cluster is now almost directly behind the other. The 'cold' clouds of gas are the cores of each cluster, which have survived the initial collision but will eventually fall back together to become one. The data reveals that the clusters have collided at a speed of over 3300 km/s. This is interesting because there are some computer models of colliding galaxy clusters that suggest that such a high speed is impossible to reach. Nevertheless, the Bullet Cluster is estimated to have a collision speed similar to the Abell 576 system. "There is now a growing body of evidence that these high collision velocities are possible," says Dupke. The job of explaining these high speeds now rests with the cosmologists. Major cluster-cluster collisions are expected to be rare, with estimates of their frequency ranging from less than one in a thousand clusters to one in a hundred. On collision, their internal gas is thrown out of equilibrium and if unrecognised, causes underestimation of its mass by between 5 and 20 percent. This is important because the masses of the various galaxy clusters are used to estimate the cosmological parameters that describe how the Universe expands. So, identifying colliding systems is extremely important to our understanding of the Universe. Dupke and colleagues are already investigating a number of other clusters that also appear to be interacting. European Space Agency |
|||||||||||||||||||||
| Related Galaxy Clusters Current Events and Galaxy Clusters News Articles Shedding light on the cosmic skeleton "Matter is not distributed uniformly in the Universe," says Masayuki Tanaka from ESO, who led the new study. "In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called 'cosmic web', in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure." Galaxy cluster smashes distance record The most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. Turbulence responsible for black holes' balancing act We live in a hierarchical Universe where small structures join into larger ones. Earth is a planet in our Solar System, the Solar System resides in the Milky Way Galaxy, and galaxies combine into groups and clusters. Largest ever survey of very distant galaxy clusters completed An international team of researchers led by a UC Riverside astronomer has completed the largest ever survey designed to find very distant clusters of galaxies. Suzaku Snaps First Complete X-ray View of a Galaxy Cluster The joint Japan-U.S. Suzaku mission is providing new insight into how assemblages of thousands of galaxies pull themselves together. The NASA/ESA Hubble Space Telescope provides new evidence for dark matter around small galaxies The NASA/ESA Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter. Ghostly glow reveals galaxy clusters in collision A team of scientists, including astronomers from the Naval Research Laboratory (NRL), have detected long wavelength radio emission from a colliding, massive galaxy cluster which, surprisingly, is not detected at the shorter wavelengths typically seen in these objects. Scientists Detect Cosmic 'Dark Flow' Across Billions of Light Years Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), scientists have identified an unexpected motion in distant galaxy clusters. The cause, they suggest, is the gravitational attraction of matter that lies beyond the observable universe. Yale Astronomer Discovers Upper Mass Limit for Black Holes here appears to be an upper limit to how big the universe's most massive black holes can get, according to new research led by a Yale University astrophysicist. Clash of clusters provides new dark matter clue A powerful collision between galaxy clusters has been captured by the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray Observatory. This clash of clusters provides striking evidence for dark matter and insight into its properties. More Galaxy Clusters Current Events and Galaxy Clusters News Articles |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
|||||||||||||||||||||