Huge "Superbubble" of Gas Blowing Out of Milky Way (Forwarded)

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Embargoed for Release: 10:00 a.m., EST, Thursday, January 12, 2006

Huge "Superbubble" of Gas Blowing Out of Milky Way

Astronomers using the National Science Foundation's Robert C. Byrd Green
Bank Telescope (GBT) have discovered a huge "superbubble" of hydrogen
gas rising nearly 10,000 light-years above the plane of our Milky Way
Galaxy. They believe the gas may be driven by supernova explosions and
the intense stellar winds from an unseen cluster of young stars in one
of our Galaxy's spiral arms.

"This giant gas bubble contains about a million times more mass than the
Sun and the energy powering its outflow is equal to about 100 supernova
explosions," said Yurii Pidopryhora, of the National Radio Astronomy
Observatory (NRAO) and Ohio University. Pidopryhora, along with Jay
Lockman of NRAO, and Joseph Shields of Ohio University, presented their
results to the American Astronomical Society's meeting in Washington, DC.

The superbubble is nearly 23,000 light-years from Earth. The astronomers
discovered it by combining numerous smaller images made with the GBT
into one large image. In addition, they added images of ionized hydrogen
in the region that were made by a University of Wisconsin optical
telescope on Kitt Peak in Arizona.

"We see that all the hydrogen gas in this region of the Galaxy is
disturbed, with many smaller outflows closer to the plane of the Galaxy
and then a giant plume of gas that forms a sort of cap on the whole
thing," Pidopryhora said. The ionized hydrogen, with atoms violently
stripped of their electrons, seems to fill the interior of the
superbubble while the neutral hydrogen forms its walls and cap.

Our Milky Way Galaxy, about 100,000 light-years across, somewhat
resembles a giant dinner plate, with most of its stars and gas residing
in a flat disk. "Gas driven outward from the plane of the Galaxy's disk
has been seen many times before, but this superbubble is particularly
large," Lockman said. "The eruption that drove this much mass so far out
of the plane has to have been unusually violent," he added.

The scientists speculate that the gas may be blown outward by the strong
stellar winds and supernova explosions from numerous massive young stars
in a cluster. "One theoretical model shows that young stars could power
an outflow that matches what we see very closely," Pidopryhora said.
According to that model, the superbubble probably is 10-30 million years
old.

"Finding this superbubble practically in our back yard is quite
exciting, because these superbubbles are very important factors in how
galaxies evolve," Lockman said.

Superbubbles, powered by supernova explosions and young stellar winds,
control the way heavy elements, produced only in the cores of stars, are
distributed throughout the galaxy, the scientists said. Those heavy
elements are then incorporated into the next generation of stars -- and
planets -- to form. "The formation of our own Sun and planets probably
was heavily influenced, if not triggered, by a nearby supernova
explosion," Lockman said.

In addition, if the outflow from superbubbles is energetic enough, it
could blow the gas into intergalactic space, never to return to the
galaxy. "This would shut down the formation of new stars in the galaxy,"
Pidopryhora explained.

The Green Bank Telescope, dedicated in 2000, is the largest
fully-steerable radio telescope in the world, with more than two acres
of collecting area in its giant dish. Located within the National Radio
Quiet Zone in West Virginia, the GBT provides extraordinary sensitivity
for observing faint radio-emitting objects in the distant Universe.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTION:
[http://www.nrao.edu/pr/2006/plume/Bubble.jpg (765KB)]
Graphic of Superbubble rising above plane of Milky Way. Art Credit: Bill
Saxton, NRAO/AUI/NSF