Ultima Thule

In ancient times the northernmost region of the habitable world - hence, any distant, unknown or mysterious land.

Wednesday, October 04, 2006

Largest 3D map of nearby galaxies released

By Aussiegirl

How interesting, to learn that our Milky Way galaxy is being tugged towards something!

Largest 3D map of nearby galaxies released - space - 03 October 2006 - New Scientist Space

NewScientist.com news service
Kelly Young

The largest three-dimensional map of galaxies in the nearby universe has been released by an international team of astronomers. It may shed light on the nature and distribution of dark matter, which cannot be seen but appears to outweigh ordinary matter by a factor of six to one.

The map probes galaxies out to 600 million light years from Earth. Other surveys have studied more distant objects, but none have explored such a wide region of space.

"It covers the whole sky," says team member John Huchra, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US. "That's what really makes it different." The map may give scientists a better clue as to where the Milky Way may be heading.

Our galaxy's motion cannot be explained simply by the general expansion of the universe, and researchers have long been trying to find the object or objects that are tugging on it. It may be pulled toward one or more superclusters, which each contain tens of thousands of galaxies.

Great Attractor
Some previous studies have suggested the most massive object in the observable universe is exerting the most influence on our galaxy's motion. This is a supercluster called Shapley that lies about 400 million light years away and spans 20 million light yeas. But the new map suggests a closer, less massive supercluster called the Great Attractor has the largest "pull" over the Milky Way. It also verified that the Great Attractor is its own supercluster and is not connected to Shapley.

Still, the superclusters observed in this survey cannot totally account for the direction of the Milky Way's travel. "So the story is not yet complete, or there's some hidden dark matter out there not well traced by the galaxies," Huchra told New Scientist.

"With this, we hope to elucidate the nature and disposition of dark matter and understand much, much more about our cosmological model and about galaxies themselves," he says.

The images were produced through the 2MASS Redshift Survey (2MRS), which mapped the distances to about 25,000 galaxies by how much their light had been stretched, or "redshifted", by the expansion of the universe. The colours and two-dimensional positions of the galaxies in the sky had been taken from the Two Micron All Sky Survey (2MASS).

The new study is led by Pirin Erdogdu of Nottingham University, UK, and will appear in the Monthly Notices of the Royal Astronomical Society.


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