Space Telescopes Find Trigger-Happy Star Formation

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Megan Watzke 617-496-7998
Chandra X-ray Center, Cambridge, Mass.
mwatzke@cfa.harvard.edu

Janet Anderson 256-544-6162
NASA Marshall Space Flight Center, Ala.
janet.l.anderson@nasa.gov

NEWS RELEASE: 2009-123 August 12, 2009

Space Telescopes Find Trigger-Happy Star Formation

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 .

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