Mapping Orion's winds (Forwarded)

News Service
Vanderbilt University

Contact:
David F. Salisbury, (615) 343-6803

1-10-2006

Mapping Orion's winds

NASHVILLE, Tenn. -- For the past few months, Bob O'Dell has been mapping
the winds blowing in the Orion Nebula, the closest stellar nursery similar
to the one in which the sun was born.

New data from the Hubble Orion Heritage Program, a major observational
effort by the Hubble Space Telescope in 2004 and 2005, have given the
Vanderbilt astronomer the information he needs to measure the stellar
winds with unprecedented detail, and he reported his early results on Jan.
11 at the annual meeting of the American Astronomical Society in
Washington D.C.

"Determining how stellar winds interact with the ambient material in
stellar nurseries like Orion is a critical factor in understanding the
process of star creation," says O'Dell, distinguished research professor
of astrophysics and an international authority on Orion.

All stars, including the Sun, give off a stream of particles as they burn.
In young, hot stars like those that form the "Trapezium" at the heart of
Orion this stream of particles is millions of times more dense and
energetic than the solar wind. Newborn stars, which are still shrouded in
thick veils of dust and gas, often eject gas and dust from their polar
regions in narrow jets, rather than broadcasting them outward in all
directions. When these stellar winds impact floating clouds of dust and
gas, they produce shock waves that erode and shape the clouds in a fashion
similar to the way in which terrestrial winds sculpt sand dunes. When they
are strong enough, such shock waves also can compress the free-floating
clouds of dust and gas, triggering the formation of new stars.

O'Dell is using these shock waves as celestial "wind socks" to plot the
direction of these winds in different parts of the nebula. By
back-tracking older, more distant shock waves to their likely points of
origin, the astronomer can also get an idea of how long major currents
have been flowing.

"When you look closely enough, you see that the nebula is filled with
hundreds of visible shock waves," the astronomer says.

In his analysis, O'Dell has identified three different types of shock
waves:

* Bow-shocks are stationary shock waves that are formed by the collision
of two steady winds and are excellent indicators of wind direction. They
are present near the hottest stars in the center of the nebula where they
show winds flowing outward at velocities of thousands of kilometers per
second. They are also present in the outer nebula where they are produced
by low velocity stellar winds of tens of kilometers per second.

* Jet-driven shocks are produced when narrow streams of gas and particles
traveling at hundreds of kilometers per second pass through gas that is
relatively stationary. There are many shockwaves of this type in the
nebula that are produced by jets of material ejected by newly formed
stars.

* Warped shocks are jet-driven shocks located in areas where the ambient
gas is not stationary but is moving in a cross current. This bends the
jets and shocks into bow-like shapes.

Using these markers, the astronomer has mapped the outflow from two of the
three regions of star formation in the nebula. Both of these regions,
labeled BN-KL and Orion-South, are located behind the glowing region of
the nebula where the light from the central stars ionizes the outer layers
of the parent molecular cloud. The specific objects that are producing
these winds in the two regions are not visible to optical telescopes but
they stand out as hot spots in infrared images.

By tracking back the farthest shockwaves produced by these outflows,
O'Dell has established that the winds blowing from BN-KL have been doing
so for 900 to 1,100 years, while those from Orion-South have been going on
for 200 to 1,500 years.

These observations were made during 104 orbits of the Hubble and provide
the most comprehensive picture ever obtained of the Orion Nebula. The data
will be combined with other Hubble and ground-based telescope observations
to create a widely available archive for research scientists interested in
this region, in addition to acting as a base for a detailed study that
should provide new insights into the conditions required for creating
stars like the sun.

For more news about Vanderbilt research, visit Exploration, Vanderbilt's
online research magazine, at
http://www.exploration.vanderbilt.edu

IMAGE CAPTIONS:

[Image 1:
http://www.newswise.com/images/uploa...ion_insert.jpg
(528KB)]
The area of the Orion Nebula in the white box is enlarged on the left to
show some of the hundreds of shock waves that crisscross the region.

Courtesy of C. Robert O'Dell

[Image 2:
http://www.newswise.com/images/uploa...rped_shock.jpg
(50KB)]
The young star at the center of the image is ejecting material in narrow
jets from both poles. The presence of a strong cross-flow is shown by the
bright bow-shock on the star's left. As a result of this cross-current,
both jets bend to the right.

Courtesy of C. Robert O'Dell