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Lt_Ripley

Gangly-Armed Galaxy Poses Star Birth Puzzle

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Gangly-Armed Galaxy Poses Star Birth Puzzle

Larry O'Hanlon, Discovery News

April 16, 2008 -- A new intensely detailed ultraviolet light and radio wave image of the nearby galaxy known as M83 is revealing an astronomical stumper: scads of newborn stars where they should not be.

The new image shows M83's gangly arms reaching 140,000 light-years beyond the galactic disk and bristling with newborn stars.

The problem is that such remote parts of a galaxy lack the dense clouds of molecular gases and the explosive events that are thought to trigger the collapse of those clouds into stellar factories. So what gives?

"It's very surprising," said astronomer Mark Seibert of the Observatories of the Carnegie Institution of Washington. Seibert is part of the team that studied the ultraviolet data collected by NASA's Galaxy Evolution Explorer satellite.

The new image blends the ultraviolet view with the radio view as collected by the National Science Foundation's Very Large Array in New Mexico. The key to finding the new stars is the new UV view, Seibert said. Young stars shine brightly in UV light.

But seeing and explaining are different matters and nobody is sure how the stars got way out in the M83 hinterlands.

"This has been somewhat of a puzzle," said astronomer Naomi McClure-Griffiths of the Australia Telescope National Facility. There has been other ultraviolet evidence from other galaxies of stars forming in remote regions for a few years, she said.

Because the new UV image of M83 was taken over a much longer exposure time than those other images of other galaxies, it reveals many more young star clusters than ever seen before in the outer limits of a galaxy. So M83 just makes the case more strongly than ever that remote star formation happens and may not even be rare.

One possible explanation is that the stars forming so far away from the galactic disk are not being made of complex molecular gases at all. Instead, they are being built out of atomic gases -- old-fashioned hydrogen and helium atoms like those that somehow got together to make the universe's first stars.

If so, they may be a great way to learn about the workings of the first stars and the workings of the early universe.

To verify that there is, indeed, hydrogen in the far-reaching realms of M83, the researchers looked to the Very Large Array, which can detect the spectral signature of that element. They were rewarded with a perfect match.

"The degree to which the ultraviolet emission and therefore the distribution of young stars follows the distribution of the atomic hydrogen gas out to the largest distances is absolutely remarkable," said Fabian Walter, another member of the discovery team and an astronomer at the Max Planck Institute for Astronomy in Germany.

All this from what was considered a very familiar galaxy located just 15 million light-years from Earth.

"What's amazing is that this is a very well known galaxy," said Seibert. "We've been looking at it for years."

http://dsc.discovery.com/news/2008/04/16/g...ars-spiral.html

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wouldnt it be great to take a spin through that sprial system? want to take a spin Lt Ripley?

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