Observations confirmed a leading theory that a
doughnut-shaped ring of material could be responsible for the formation
of massive
stars, scientists reported today.
Smaller stars
typically form when clouds of dust and gas collapse
into a ball of compact material.
Stars that are 10 times more massive than the Sun, however, generate powerful stellar
radiation, which can prevent the accumulation of material.
Doughnut disk
One model suggests that the radiation shoots out stronger at
the poles of the star and is much weaker in the equator regions. Matter
therefore forms a whirling disk, much like a doughnut, around the equator of
the star. Most of the radiation escapes without hitting the disk so material
keeps falling onto the star from the disk.
"If this model is correct, there should be material
falling inward, rushing outward and rotating around the star all at the same
time," said leader Maria Teresa Beltran, of the University of Barcelona in
Spain.
Beltran and colleagues found one such star, G24 A1, a young
object some 25,000 light-years from Earth and up to 20 times more massive than
our Sun.
"For the first time, we have revealed the simultaneous
presence in the same massive object of material moving outward, material moving
inward, and rotation," Beltran said. "These three elements, outflow,
infall and rotation, are commonly found during the formation process of low
mass stars."
Tracing gas
Using the National Science Foundation's Very
Large Array (VLA) radio telescope, the researchers traced the inward motion
of the material.
"By studying the velocity field of the gas we
detected a Doppler
shift toward positive velocities of the surrounding gas, which indicates
that the gas is moving inward the star," Beltran told SPACE.com.
The Doppler shift
in the frequency of radio waves emitted by ammonia molecules present in the
material gave scientist information on the motion of the gas.
Beltran says that the detection of gas falling inward toward
the star is an important milestone and supports one of several proposed ways
for massive stars to accumulate their great bulk. But she does not exclude the
theory of smaller star collision.
"We
think that the coalescence mechanism to form massive stars could still be
required to form even more massive stars, or to form massive stars where the
stellar densities are very large."
The study is detailed in the Sept. 28 issue of the journal Nature.
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