Intergalactic dust detected by analysis of quasars' colors

Washington, Feb 27 (ANI): A team of astronomers from the Sloan Digital Sky Survey (SDSS) have detected intergalactic dust by analyzing the colors of distant quasars whose light passes in the vicinity of foreground galaxies on its way to the Earth.

"Galaxies contain lots of dust, most of it formed in the outer regions of dying stars," said team leader Brice Menard of the Canadian Institute for Theoretical Astrophysics.

"The surprise is that we are seeing dust hundreds of thousands of light-years outside of the galaxies, in intergalactic space," he added.

Dust grains block blue light more effectively than red light, according to astronomer Ryan Scranton of the University of California, Davis, another member of the discovery team.

"We see this when the sun sets: light rays pass through a thicker layer of the atmosphere, absorbing more and more blue light, causing the sun to appear reddened," he said.

"We find similar reddening of quasars from intergalactic dust, and this reddening extends up to ten times beyond the apparent edges of the galaxies themselves," he added.

The team analyzed the colors of about 100,000 distant quasars located behind 20 million galaxies, using images from SDSS-II.

"Putting together and analyzing this huge dataset required cutting-edge ideas from computer science and statistics," said team member Gordon Richards of Drexel University.

"Averaging over so many objects allowed us to measure an effect that is much too small to see in any individual quasar," he added.

Supernova explosions and "winds" from massive stars drive gas out of some galaxies, Menard explained, and this gas may carry dust with it. Alternatively, the dust may be pushed directly by starlight.

"Our findings now provide a reference point for theoretical studies," said Menard.

Intergalactic dust could also affect planned cosmological experiments that use supernovae to investigate the nature of "dark energy," a mysterious cosmic component responsible for the acceleration of the expansion of the universe.

"Just like household dust, cosmic dust can be a nuisance," said Scranton. "Our results imply that most distant supernovae are seen through a bit of haze, which may affect estimates of their distances," he added. (ANI)