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KULVINDER SINGH CHADHA ASTRONOMY NOW Posted: 27 February, 2009 Hold your breath: we may be living in a smoky Universe that dims light from distant objects such as quasars, or so say astronomers working on the Sloan Digital Sky Survey (SDSS). Just like when a sunset appears reddened because it has to travel through more of Earth’s atmosphere, light from quasars could appear redder because it has to travel through the dust of intervening galaxies. “Galaxies contain lots of dust, most of it formed in the outer regions of dying stars,” says study team leader Dr 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.” The team’s findings have been published in the Monthly Notices of the Royal Astronomical Society.
Dust in galaxies often drifts off to mix with interstellar gas. The new analysis of quasar colors shows that galaxies also expel dust to distances of several hundred thousand light years. Image: Sloan Digital Sky Survey. Using images from SDSS 2, the team analyzed 100,000 distant quasars, which were located behind at least 20 million galaxies. “Putting together and analyzing this huge dataset required cutting-edge ideas from computer science and statistics,” says 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 Why could this ‘haze’ be filling the Universe instead of remaining in its galactic confines? There are two theories. In one, supernovae explosions and strong winds from massive stars push gas and dust out of galaxies. In the other theory, this process occurs by radiation pressure on the dust by starlight. “Our findings now provide a reference point for theoretical studies,” says Menard. Whatever the mechanism that drives dust out into intergalactic space, its presence there could be a problem. Cosmological observations that make use of distant quasars and supernovae to gauge the size and age of the Universe, as well as the presence of the mysterious ‘dark energy’ (thought to be responsible for the expansion of the Universe) could be affected. However, Menard says that the presence of dust doesn’t remove the need for dark energy and that any estimates would merely have to account for the dust. He adds, “These
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