Astronomers have found cosmic clumps so
dark, dense and dusty that they throw the deepest shadows ever recorded.
Image credit: NASA/JPL-Caltech/University of Zurich. Full image and caption
Astronomers have found cosmic clumps so dark, dense and dusty that
they throw the deepest shadows ever recorded. Infrared observations from
NASA's Spitzer Space Telescope of these blackest-of-black regions
paradoxically light the way to understanding how the brightest stars
form.
The clumps represent the darkest portions of a huge, cosmic cloud of
gas and dust located about 16,000 light-years away. A new study takes
advantage of the shadows cast by these clumps to measure the cloud's
structure and mass.
The dusty cloud, results suggest, will likely evolve into one of the
most massive young clusters of stars in our galaxy. The densest clumps
will blossom into the cluster's biggest, most powerful stars, called
O-type stars, the formation of which has long puzzled scientists. These
hulking stars have major impacts on their local stellar environments
while also helping to create the heavy elements needed for life.
"The map of the structure of the cloud and its dense cores we have
made in this study reveals a lot of fine details about the massive star
and star cluster formation process," said Michael Butler, a postdoctoral
researcher at the University of Zurich in Switzerland and lead author
of the study, published in The Astrophysical Journal Letters.
The state-of-the-art map has helped pin down the cloud's mass to the
equivalent of 7,000 suns packed into an area spanning about 50
light-years in diameter. The map comes courtesy of Spitzer observing in
infrared light, which can more easily penetrate gas and dust than
short-wavelength visible light. The effect is similar to that behind the
deep red color of sunsets on smoggy days -- longer-wavelength red light
more readily reaches our eyes through the haze, which scatters and
absorbs shorter-wavelength blue light. In this case, however, the
densest pockets of star-forming material within the cloud are so thick
with dust that they scatter and block not only visible light, but also
almost all background infrared light.
Observing in infrared lets scientists peer into otherwise inscrutable
cosmic clouds and catch the early phases of star and star cluster
formation. Typically, Spitzer detects infrared light emitted by young
stars still shrouded in their dusty cocoons. For the new study,
astronomers instead gauged the amount of background infrared light
obscured by the cloud, using these shadows to infer where material had
lumped together within the cloud. These blobs of gas and dust will
eventually collapse gravitationally to make hundreds of thousands of new
stars.
Most stars in the universe, perhaps our sun included, are thought to
have formed en masse in these sorts of environments. Clusters of
low-mass stars are quite common and well-studied. But clusters giving
birth to higher-mass stars, like the cluster described here, are scarce
and distant, which makes them harder to examine.
"In this rare kind of cloud, Spitzer has provided us with an
important picture of massive star cluster formation caught in its
earliest, embryonic stages," said Jonathan Tan, an associate professor
of astronomy at the University of Florida, Gainesville, and co-author of
the study.
The new findings will also help reveal how O-type stars form. O-type
stars shine a brilliant white-blue, possess at least 16 times the sun's
mass and have surface temperatures above 54,000 degrees Fahrenheit
(30,000 degrees Celsius). These giant stars have a tremendous influence
on their local stellar neighborhoods. Their winds and intense radiation
blow away material that might draw together to create other stars and
planetary systems. O-type stars are short-lived and quickly explode as
supernovas, releasing enormous amounts of energy and forging the heavy
elements needed to form planets and living organisms.
Researchers are not sure how, in O-type stars, it is possible for
material to accumulate on scales of tens to 100 times the mass of our
sun without dissipating or breaking down into multiple, smaller stars.
"We still do not have a settled theory or explanation of how these
massive stars form," said Tan. "Therefore, detailed measurements of the
birth clouds of future massive stars, as we have recorded in this study,
are important for guiding new theoretical understanding."
NASA's Jet Propulsion Laboratory, Pasadena, California, 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. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA.
For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, California
whitney.clavin@jpl.nasa.gov
Jet Propulsion Laboratory, Pasadena, California
whitney.clavin@jpl.nasa.gov
