image: By observing distant background quasars positioned behind foreground galaxies, the Cosmic Origins Spectrograph has detected huge halos of hot gas surrounding galaxies like the one shown in this image from the Sloan Digital Sky Survey. The light emitted by the hot gas is invisible; its presence is inferred by the particular colors of light absorbed from the background quasar by the foreground material. In this way, large (and otherwise undetectable) reservoirs of "circumgalactic matter" surrounding galaxies have been revealed. This image relates to a paper that appeared in the Nov. 18, 2011, issue of Science, published by AAAS. The paper, by Todd Tripp at University of Massachusetts in Amherst, Ma., and colleagues, was titled, “The Hidden Mass and Large Spatial Extent of a Post-Starburst Galaxy Outflow.” view more
Credit: Image courtesy of Todd M. Tripp, Sloan Digital Sky Survey