Gangly-Armed Galaxy Poses Star Birth Puzzle

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.