Optical and mm-wave overlay of dark cloud

Star formation is a longer process than previously thought,
and is heavily dependent on outside events, such as supernova
explosions, to trigger it, a team of astronomers has concluded.
The scientists reached their conclusions after making a
detailed study of a number of the dark gas clouds in which new
stars are formed.

“Our observations indicate that we need to drastically revise our
ideas about the very early stages of star formation,” said Claire
Chandler, an astronomer at the National Radio Astronomy Observatory
(NRAO) in Socorro, New Mexico. Chandler, who worked with John
Richer and Anja Visser at the Mullard Radio Astronomy Observatory
in the United Kingdom, presented the results at the American
Astronomical Society’s meeting in Washington, D.C.

The astronomers observed the gas clouds with the SCUBA camera
on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. This
instrument is sensitive to submillimeter-wavelength radiation,
which lies between radio waves and infrared waves in the
electromagnetic spectrum. They studied clouds that previously
had been observed with optical and infrared telescopes. The
SCUBA images allowed them to see aspects of the clouds not
visible at other wavelengths.

Some young “protostars” are so deeply embedded in their parent
gas clouds that they are invisible to infrared telescopes, while
others have become visible by consuming and blowing away much of
their surrounding clouds. Earlier studies had indicated that the
“invisible” stars are only about one-tenth as common as those
visible to infrared telescopes.

“What we see in our study, however, is equal numbers of both types,”
said Chandler, who added, “This means that both stages probably have
about the same lifetime — roughly 200,000 years each.”

Another conclusion coming from the study is that star formation is
heavily dependent on a triggering event to get it started. Such
a triggering event might be the shock wave from a supernova explosion
that causes gas clouds to begin the gravitational collapse that
ultimately results in a new star.

Another challenge to traditional wisdom about the early stages of
star formation came in the team’s analysis of data on starless
cores — gas clouds that have not yet begun their collapse into
stars. The astronomers found that the starless cores in their study
are on the verge of collapsing, and probably have shorter lifetimes
than previously thought.

“This means that, contrary to what we thought before, you don’t need
strong magnetic fields to hold these things up against gravitational
collapse, because they don’t last that long,” Chandler said. Much
theoretical work on early star formation that focuses on the role
of magnetic fields may need revision, the study indicates.

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