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Space Telescopes Find Trigger-Happy Star Formation



 
 
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Old August 12th 09, 08:21 PM posted to sci.space.news
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Default Space Telescopes Find Trigger-Happy Star Formation

http://www.jpl.nasa.gov/news/news.cfm?release=2009-123

Space Telescopes Find Trigger-Happy Star Formation
Jet Propulsion Laboratory
August 12, 2009

PASADENA, Calif. -- A new study from two of NASA's Great Observatories
provides fresh insight into how some stars are born, along with a
beautiful new image of a stellar nursery in our Milky Way galaxy. The
research shows that radiation from massive stars may trigger the
formation of many more stars than previously thought.

While astronomers have long understood that stars and planets form
from
the collapse of a cloud of gas, the question of the main causes of
this
process has remained open.

One option is that the cloud cools, gravity gets the upper hand, and
the
cloud falls in on itself. The other possibility is that a "trigger"
from
some external source -- like radiation from a massive star or a shock
from a supernova -- initiates the collapse. Some previous studies have
noted a combination of triggering mechanisms in effect.

By combining observations of the star-forming cloud Cepheus B from the
Chandra X-ray Observatory and the Spitzer Space Telescope, researchers
have taken an important step in addressing this question. Cepheus B is
a
cloud of mainly cool molecular hydrogen located about 2,400 light
years
from Earth. There are hundreds of very young stars inside and around
the
cloud -- ranging from a few million years old outside the cloud to
less
than a million in the interior -- making it an important testing
ground
for star formation.

"Astronomers have generally believed that it's somewhat rare for stars
and planets to be triggered into formation by radiation from massive
stars," said Konstantin Getman of Penn State University, University
Park, Pa., lead author of the study. "Our new result shows this belief
is likely to be wrong."

This particular type of triggered star formation had previously been
seen in small populations of a few dozen stars, but the latest result
is
the first time it has been clearly observed in a rich population of
several hundred stars.

While slightly farther away than the famous Orion star-forming region,
Cepheus B is at a better orientation for astronomers to observe the
triggering process. The Chandra observations allowed the astronomers
to
pick out young stars within and around Cepheus B. Young stars have
turbulent interiors that generate highly active magnetic fields,
which,
in turn, produce strong and identifiable X-ray signatures.

The Spitzer data revealed whether the young stars have a disk of
material (known as "protoplanetary" disks) around them. Since they
only
exist in very young systems where planets are still forming, the
presence of protoplanetary disks -- or lack thereof -- is an
indication
of the age of a star system.

The new study suggests that star formation in Cepheus B is mainly
triggered by radiation from one bright, massive star outside the
molecular cloud. According to theoretical models, radiation from this
star would drive a compression wave into the cloud-triggering star
formation in the interior, while evaporating the cloud's outer layers.
The Chandra-Spitzer analysis revealed slightly older stars outside the
cloud, and the youngest stars with the most protoplanetary disks in
the
cloud interior -- exactly what is predicted from the triggered star
formation scenario.

"We essentially see a wave of star and planet formation that is
rippling
through this cloud," said co-author Eric Feigelson, also of Penn
State.
"It's clear that we can learn a lot about stellar nurseries by
combining
data from these two Great Observatories."

A paper describing these results was published in the July 10 issue of
the Astrophysical Journal. The team of astronomers that worked with
Getman and Feigelson also included Kevin Luhman and Gordon Garmire
from
Penn State; Aurora Sicilia-Aguilar from Max-Planck-Institut fur
Astronomie in Germany; and Junfeng Wang from Harvard-Smithsonian
Center
for Astrophysics, Cambridge, Mass.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science
and
flight operations from Cambridge, Mass. NASA's Jet Propulsion
Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science
operations are conducted at the Spitzer Science Center at the
California
Institute of Technology in Pasadena. Caltech manages JPL for NASA. The
Spitzer observations were taken during the observatory's "cold"
mission,
before its coolant ran out and it began operating at a warmer
temperature.

The new image and information about Spitzer are online at
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer
..
The image and information about Chandra are online at
http://chandra.harvard.edu and http://chandra.nasa.gov .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.


Megan Watzke 617-496-7998
Chandra X-ray Center, Cambridge, Mass.


Janet Anderson 256-544-6162
NASA Marshall Space Flight Center, Ala.


2009-123
 




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