ABCnews

Understanding Heavenly Halos

Looking to Supernovae as the

Source

By Kenneth Chang

ABCNEWS.com

A T L A N T A, Jan. 12 - Our Milky Way galaxy is bathed in the

glow of ultrahot gas likely blown out by the explosions of

dying stars.

University of Wisconsin astronomer Blair Savage described it as a

"galactic fountain" where supernovae explosions blast interstellar gas

upward and downward away from the galaxy's central disk, which

then, tens of millions of years later, falls back to the center by gravity.

Astronomers have known for more than four decades about the gas

halo, which extends 5,000 to 10,000 light-years above and below the

central galactic disk, but weren't sure what was feeding it. Some

hypothesized ultraviolet radiation may have been cause of the glow.

However, data from NASA's Far Ultraviolet Spectroscopic

Explorer, FUSE for short, shows the presence of oxygen ions where

five of their eight electrons have been stripped away. That is a telltale

sign that the gases had been heated to half a million degrees

Fahrenheit or hotter by the blast waves of supernovae.

"It's hard to create other than by collisions in hot gas," Savage

says.

The findings were presented today at the American Astronomical

meeting in Atlanta.

An Enlightening FUSE

FUSE, launched last June, is now "open for business and is already

producing groundbreaking science," says George Sonneborn of

NASA's Goddard Space Flight Center in Greenbelt, Md.

FUSE is designed to analyze ultraviolet light of wavelengths

shorter than can be seen with the Hubble Space Telescope or with the

human eye. "No one had made observations like this for the last 25

years," Sonneborn says.

FUSE is about 10,000 times more sensitive than a satellite called

Copernicus that operated in the 1970s.

Starting this year, FUSE is expected to start studying deuterium, a

fossil atom left from the astronomical Big Bang that astronomers

believe gave birth to the universe billions of years ago.

FUSE has also seen the telltale signs of molecular hydrogen -

where two hydrogen atoms have bonded together. Molecular

hydrogen is the primary ingredient in the creation of stars.

Looking for Lifeblood

"Molecular hydrogen is the

lifeblood of a galaxy," says J.

Michael Shull of the University

of Colorado. "We did see it

nearly everywhere."

In another set of FUSE

observations, researchers found

that the stellar wind thrown out

by seemingly identical

supermassive stars differed

depending on the age of the

parent galaxy. Researchers led

by John Hutchings of the

National Research Council of Canada examined two short-lived

stars, one in the Large Magellanic Cloud and one in the Small

Magellanic Cloud. The Magellanic Clouds are two small nearby

galaxies.

What they found is that the star in the Large Magellenic Cloud

expelled its stellar wind - material blown out by its starlight -

considerably faster than its counterpart in the Small Magellanic

Cloud. That probably reflects differing concentrations of heavier

elements between the two galaxies.

"It's weird," Hutchings says. "We don't know why it's different.

We just know it is."