Illustration of a star cluster forming from the
collision of turbulent molecular clouds, which appear as dark shadows in
front of the background galactic star field.Credits: NASA/SOFIA/Lynette Cook. Hi-res image
Illustration of the molecular clouds surrounded by
atomic envelopes, in green, which have been detected by SOFIA via
emission from ionized carbon. The spatial offset and motions of these
envelopes confirm predictions of simulations of cloud collisions.Credits: NASA/SOFIA/Lynette Cook. Hi-res image
The sun, like all stars, was born in a giant cold cloud of molecular gas
and dust. It may have had dozens or even hundreds of stellar siblings –
a star cluster
– but these early companions are now scattered throughout our Milky Way
galaxy. Although the remnants of this particular creation event have
long since dispersed, the process of star birth continues today within
our galaxy and beyond. Star clusters are conceived in the hearts of
optically dark clouds where the early phases of formation have
historically been hidden from view. But these cold, dusty clouds shine
brightly in the infrared, so telescopes like the Stratospheric
Observatory for Infrared Astronomy, SOFIA, can begin to reveal these
long-held secrets.
Traditional models claim that the force of gravity may be solely
responsible for the formation of stars and star clusters. More recent
observations suggest that magnetic fields, turbulence, or both are also
involved and may even dominate the creation process. But just what
triggers the events that lead to the formation of star clusters?
Astronomers using SOFIA’s instrument, the German Receiver for
Astronomy at Terahertz Frequencies, known as GREAT, have found new
evidence that star clusters form through collisions between giant
molecular clouds.
The results were published in the Monthly Notices of the Royal Astronomical Society.
"Stars are powered by nuclear reactions that create new chemical
elements," said Thomas Bisbas, a postdoctoral researcher at the
University of Virginia, Charlottesville, Virginia, and the lead author
on the paper describing these new results. "The very existence of life
on earth is the product of a star that exploded billions of years ago,
but we still don't know how these stars — including our own sun — form."
Researchers studied the distribution and motion of ionized carbon
around a molecular cloud where stars can form. There appear to be two
distinct components of molecular gas colliding with each other at speeds
of more than 20,000 miles per hour. The distribution and velocity of
the molecular and ionized gases are consistent with simulations of cloud
collisions, which indicate that star clusters form as the gas is
compressed in the shock wave created as the clouds collide.
“These star formation models are difficult to assess
observationally,” said Jonathan Tan, a professor at Chalmers University
of Technology in Gothenburg, Sweden, and the University of Virginia, and
a lead researcher on the paper. “We’re at a fascinating point in the
project, where the data we are getting with SOFIA can really test the
simulations.”
While there is not yet scientific consensus on the mechanism
responsible for driving the creation of star clusters, these SOFIA
observations have helped scientists take an important step toward
unraveling the mystery. This field of research remains an active one,
and these data provide crucial evidence in favor of the collision model.
The authors expect future observations will test this scenario to
determine if the process of cloud collisions is unique to this region,
more widespread, or even a universal mechanism for the formation of star
clusters.
“Our next step is to use SOFIA to observe a larger number of
molecular clouds that are forming star clusters,” added Tan. “Only then
can we understand how common cloud collisions are for triggering star
birth in our galaxy.”
SOFIA is a Boeing 747SP jetliner modified to carry a 106-inch
diameter telescope. It is a joint project of NASA and the German
Aerospace Center, DLR. NASA’s Ames Research Center in California’s
Silicon Valley manages the SOFIA program, science and mission operations
in cooperation with the Universities Space Research Association
headquartered in Columbia, Maryland, and the German SOFIA Institute
(DSI) at the University of Stuttgart. The aircraft is maintained and
operated from NASA’s Armstrong Flight Research Center Hangar 703, in
Palmdale, California.
Media Point of Contact
Nicholas A. Veronico
Nicholas.A.Veronico@nasa.gov • SOFIA Science Center
NASA Ames Research Center, Moffett Field, California
Nicholas A. Veronico
Nicholas.A.Veronico@nasa.gov • SOFIA Science Center
NASA Ames Research Center, Moffett Field, California
Editor: Kassandra Bell
