Space is not quite as empty as everyone believed, astronomers have discovered. Instead, the vast expanses between the galaxies appears to be filled with a smoke-like haze.
It gives itself away by dimming the light of distant objects in the universe and subtly changing their colours.
Astronomers discovered the haze, made up of fine dust particles, while compiling a detailed photographic album of the sky called the Sloan Digital Sky Survey.
They analysed the glow from around 100,000 remote quasars – the violently active hearts of ancient galaxies in the farthest reaches of the universe.
The light from the quasars became slightly reddened as it passed through the space between newer galaxies closer to home.
Discovery team leader Brice Menard, of the Canadian Institute for Theoretical Astrophysics, said today: “Galaxies contain lots of dust, most of it formed in the outer regions of dying stars. The surprise is that we are seeing dust hundreds of thousands of light-years outside of the galaxies, in intergalactic space.”
Astronomers will now try to work out what has spread the smokey haze of dust between the galaxies. Menard said supernova explosions and “winds” from massive stars drive gas out of some galaxies. It was possible that this gas might carry dust with it. Alternatively, the dust could be pushed directly by starlight.
Colleague Ryan Scranton, of the University of California, said the dimming was similar to that of the Sun at dusk when it appeared more 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.”
Scranton added: “Just like household dust, cosmic dust can be a nuisance. Our results imply that most distant supernovae are seen through a bit of haze, which may affect estimates of their distances.”
The Sloane Digital Sky Survey has been the source of the vast number of images used by volunteers to classify galaxies in the Galaxy Zoo project.
Picture: Dust shows up as dark lanes within the edge-on spiral galaxy NGC4565 pictured in the Sloan Digital Sky Survey. The intergalactic haze may be dust which has escaped such a galaxy. (Photo: SDSS-II).