Newly Seen Force May Help Gravity in Star Formation:
Scientists have pierced through a dusty stellar nursery to capture the earliest and most
detailed view of a collapsing gas cloud turning into a star, analogous to a baby's first ultrasound.
The observation, made primarily with the European Space Agency's
XMM-Newton observatory, suggests that some unrealized, energetic
process - likely related to magnetic fields - is superheating the
surface of the cloud core, nudging the cloud ever closer to becoming
a star.
The observation marks the first clear detection of X-rays from
a nascent yet frigid precursor to a star, called a Class 0 protostar,
far earlier in a star's evolution than most experts in this field
thought possible. X-rays are produced in space by processes that
release a lot of energy and heat. The surprise detection of X-rays
from such a cold object reveals that matter is falling toward the
protostar core 10 times faster than expected from gravity alone.
"We are seeing star formation at its embryonic stage,"
said Dr. Kenji Hamaguchi, a NASA-funded researcher at NASA Goddard
Space Flight Center in Greenbelt, Md., lead author on a report in
The Astrophysical Journal. "Previous observations have captured
the shape of such gas clouds but have never been able to peer inside.
The detection of X-rays this early indicates that gravity alone
is not the only force shaping young stars." Supporting data
came from NASA's Chandra X-ray Observatory, Japan's Subaru telescope
in Hawaii, and the University of Hawaii 2.2 metre telescope. Hamaguchi's
team discovered X-rays from a Class 0 protostar in the R Corona
Australis star-forming region, about 500 light years from Earth.
Class 0 is the youngest class of protostellar object, about 10
000 to 100 000 years into the assimilation process. The cloud temperature
is about 33 K (-240 °C). After a few million years, nuclear
fusion ignites at the center of the collapsing protostellar cloud,
and a new star is formed.
The team speculates that magnetic fields in the spinning protostar
core accelerate infalling matter to high speeds, producing high
temperatures and X-rays in the process. These X- rays can penetrate
the dusty region to reveal the core.
"This is no gentle freefall of gas," said Dr. Michael
Corcoran of NASA Goddard, a co-author on the report. "The X-ray
emission shows that forces appear to be accelerating matter to high
speeds, heating regions of this cold gas cloud to over 100 million
degrees Fahrenheit (around 55 million degress Celsius). The X-ray
emission from the core gives us a window to probe the hidden processes
by which cold gas clouds collapse to stars."
Hamaguchi likened the generation of X-rays in the Class 0 protostar
to what happens during solar flares on our Sun. The solar surface
has lots of magnetic loops, which sometimes get tangled and release
large amounts of energy. This energy can accelerate electrically-charged
particles (electrons and ionized atoms) to velocities of 7 million
miles an hour. The particles smash against the solar surface and
create X-rays. Similarly tangled magnetic fields might be responsible
for X-rays observed by Hamaguchi and his collaborators.
The detection of magnetic fields from an extremely young Class
0 protostar provides a crucial link in understanding the star formation
process, because magnetic field loops are believed to play a critical
role in moderating the cloud collapse. Only electrically-charged
particles, called ions, respond to magnetic fields. The scientists
are not sure where the magnetic fields or ions come from. However,
X-rays will ionize atoms, creating more ions to feed the magnet
and create more X-rays.
The team used XMM-Newton for its powerful light-collecting capability,
necessary for this type of observation where so few X-rays penetrate
the dusty region, and the exquisite resolving power of Chandra to
pinpoint the X-ray source position. The team used the infrared Subaru
telescope to determine the protostar's age.
"The age is based on a well-established chart of spectra,
or characteristics of the infrared light, as the protostar evolves
over the course of a million years," said Ko Nedachi, a doctoral
student at the University of Tokyo who led the Subaru observation.
The science team also includes Drs. Rob Petre and Nicholas White
of NASA Goddard, Dr. Beate Stelzer of the Astronomy Observatory
in Palermo, Italy, and Dr. Naoto Kobayashi of University of Tokyo.
Kenji Hamaguchi is funded through the National Research Council;
Michael Corcoran is funded through Universities Space Research Association.
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