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Intergalactic Dust Could Be Messing Up Observations, Calculations

Spiral galaxies seen edge-on often show dark lanes of interstellar dust blocking light from the galaxy's stars, as in this image of the galaxy NGC 4565 from the Sloan Digital Sky Survey (SDSS-II).

Spiral galaxies seen edge-on often show dark lanes of interstellar dust blocking light from the galaxy's stars, as in this image of the galaxy NGC 4565 from the Sloan Digital Sky Survey (SDSS-II).

“Just like household dust, cosmic dust can be a nuisance,” said astronomer Ryan Scranton of the University of California, Davis. Scranton is part of a team of researchers from the Sloan Digital Sky Survey that have been analyzing the colors of distant quasars whose light passes in the vicinity of foreground galaxies on its way to the Earth. What they found is that the vast expanses of intergalactic space appear to be filled with a haze of tiny, smoke-like “dust” particles that dim the light from distant objects and subtly change their colors. “Galaxies contain lots of dust, most of it formed in the outer regions of dying stars,” said team leader Brice Ménard 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.”

An implication of this finding means that since most distant supernovae are seen through some haze, our current estimates of their distances may be affected.

Dust grains block blue light more effectively than red light. “We see this when the sun sets: light rays pass through a thicker layer of the atmosphere,” said Scranton, “absorbing more and more blue light, causing the sun to appear reddened. 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.”

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.”

Supernova explosions and “winds” from massive stars drive gas out of some galaxies, Ménard 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 Ménard.

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.

Intergalactic dust doesn’t remove the need for dark energy to explain current supernova data, Ménard explained, but it may complicate the interpretation of future high-precision distance measurements. “These experiments are very ambitious in their goals,” said Ménard, “and subtle effects matter.”

The new findings are reported in a paper titled “Measuring the galaxy-mass and galaxy-dust correlations through magnification and reddening,” submitted to the journal Monthly Notices of the Royal Astronomical Society, and posted today on the web site arXiv.org.

Source: Sloan Digital Sky Survey


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • ND February 27, 2009, 11:46 AM


    The following wiki entry is a good overview of redshift and how it’s measured.


    Redshift can be measured for wavelengths outside of the visible spectrum.

  • ND February 27, 2009, 12:06 PM


    What career are you in?

  • robbi February 27, 2009, 4:50 PM

    In the relatively near future with advanced space scopes and ground based scopes using various filters and specialized detectors, they will eventually find the zone of ‘nothing’, this is NOT the area where the Universe ends, it is part of space that has receded faster than the speed of light-this does not break Einsteins rule as space itself is expanding and not the objects like ‘baby galaxies’. These objects have receded into ‘nothing’ because they are in space > speed of light and forever gone from view, dispite the best detectors available and would be dimmer than the Universes ‘glow’ from the leftover of the Big Bang.
    To get past this glow is to create gravitrons detectors which is thousands of times more difficult than creating a true neutrino ‘scope’ or viewing ALL neutrinos in ‘movement’ which is far,far beyond out current technology
    and knowledge, this is probably something in the 3000 millennium
    In short, they will find the edge of zone of ‘nothing’ or objects in space that travel > speed of light forever gone, even if they ever create a gravitron detector, those objects past the zone of ‘ nothing’ is forever gone from view

  • Will February 28, 2009, 6:04 PM