Australian astronomers map 110,000 galaxies

Astronomers have completed the most detailed survey of 110,000 galaxies in the nearby universe, which will not only reveal their locations but also where they're heading, how fast and why.

"It's like taking a snapshot of wildebeest on the African plain. We can tell which waterholes they're heading to, and how fast they're travelling," said Heath Jones of the Anglo-Australian Observatory (AAO), who heads the Six-Degree Field Galaxy Survey (6dFGS).

Galaxies are tugged around by one another's gravity. By measuring the galaxies' movements, the researchers can map the gravitational forces at work in the local universe, and so show how matter, seen and unseen, is distributed.

Giant superclusters of galaxies are huge concentrations of mass, but they can't be weighed accurately by looking at their light alone. "Light can be obscured, but you can't hide gravity," said Jones.

The survey was carried out with the 1.2-metre Britain Schmidt Telescope, which is operated by the Siding Spring Observatory in New South Wales, Australia.

Broader and shallower than previous comparable surveys - it covered twice as much sky as the Sloan Digital Sky Survey - it has recorded the positions of more than 110,000 galaxies over more than 80 percent of the Southern sky, out to about 2,000 million light-years from the Earth.

The survey shows strings and clusters of nearby galaxies on large scales in unprecedented detail, and has revealed more than 500 voids - "empty" space with no galaxies.

The special aspect of this survey is that it will let the researchers disentangle two causes of galaxy movements. As well as being pulled on by gravity, galaxies also ride along with the overall expansion of the universe.

For about 10 percent of their galaxies, the 6dFGS researchers will tease apart these two velocity components: the one associated with the universe's expansion, and the one representing a galaxy's individual, "peculiar", motion, said a statement from the Anglo-Australian Observatory (AAO).

These results were presented early this month at an international meeting in Malaysia by Matthew Colless, director of the AAO.