UH astronomers verify collision in the cosmos
POSTED: Sunday, April 26, 2009
University of Hawaii-Manoa astronomers have documented a collision of four galaxy clusters 5.4 billion light years from Earth.
Using data from space and ground-based telescopes, graduate student Cheng-Jiun Ma and astronomer Harald Ebeling of the Institute for Astronomy determined the three-dimensional geometry and motion of galaxies in the MACSJO717 cluster system.
They found evidence that a 13-million-light-year-long stream of galaxies, gas and dark matter—known as a filament—was causing repeated collisions in the cluster.
Ebeling said he thinks of filaments as "cosmic freeways" providing infrastructure for gas, galaxies and dark matter to fill up as they rush to a junction with a cluster. "That interface between a filament and cluster is where everything comes crashing together."
Ma was lead author of the study, which appeared in Astrophysical Journal Letters. Elizabeth Barrett did earlier work on MACSJO717 as an institute graduate student, Ebeling said.
"We've seen a large number of messy clusters, but this one takes the biscuit," he said in an interview. "It completely baffled us."
The researchers figured it out using combined data from NASA's Chandra X-ray Observatory, the Hubble Space Telescope and Keck Observatory on Mauna Kea.
The general picture is that galaxy clusters—the largest objects bound by gravity in the universe—grow where filaments intersect, Ebeling said.
To see the interaction between a filament and galaxy cluster has been "an elusive goal of cosmology," he said. "It got us totally excited about this." He said MACSJO717 is "a wonderful system for studying how clusters grow as material falls into them along filaments." Filaments are hard to detect but matter can be observed when the density becomes high enough, he said.
Besides the "enormous pileup" of galaxies, Ma said MACSJO717 is remarkable because each collision releases energy in the form of heat and "it has one of the highest temperatures ever seen in such a system."
Ma is seeking a Chandra grant to continue their studies. The researchers believe they can learn a lot more from MACSJO717 "about how structure in our universe grows and evolves," Ma said.