A false-color
image of the Orion Nebula as seen in the combined optical and infrared
with the Hubble and Spitzer Space Telescopes. A new study of a very
young, massive star embedded in the region finds evidence for magnetic
fields that have shaped and helped collimate the bipolar jets. Credit: NASA; Hubble and Spitzer. Low Resolution Image (jpg)
The Orion Nebula, one of the most famous
sights in the night sky, contains several clusters of hot young stars,
whose intense ultraviolet radiation prompts the gas and dust to glow
brightly. The nebula is about 1360 light-years away, making it the
closest nursery of massive stars and one of the best-studied such
regions. But despite its fame, brightness, and proximity,
astronomers still do not understand it very well. It contains dramatic
outflows of material, for example, that may be driven by a single star
or perhaps by a cluster of stars -- astronomers are not sure. The reason
for this ignorance is in part because the nebula is so crowded with
stars, and in part because its dust obscures many regions from optical
view.
The brightest object in the nebula shines with as much light as 100,000
suns. In the past decade astronomers found that this source was itself
comprised of several smaller ones, including an intense radio
source called "Source I." It is enigmatic, to put it mildly. Its
motions suggest that it
may have been ejected from another system just a few hundred years ago;
other evidence suggests it is surrounded by a circumstellar disk of
material containing natural masers (radio wavelength analogues of
lasers). Such masers typically signal dense material around young stars.
CfA astronomer Lincoln Greenhill and four of his colleagues have been
tracking the motions of the gas near Source I for over nine years using
the Very Large Array radio telescopes. The facility is capable of
resolving distances at Orion of only about twenty astronomical units
(AU) - smaller than our solar system (the average distance of Uranus
from the Sun is 19 AU). The goal of their research was to unravel the
relative roles of the three principal processes driving massive star
formation: gravity, radiation pressure, and magnetism. The effects these
processes are somewhat mysterious because it is so difficult to study
the densely packed regions of activity near the surface of the star
where stellar winds are launched and collimated (not to mention that the
region is heavily obscured by dust).
The astronomers report finding a dynamically active, bipolar flow in the
source, with strong shocks, motions of over 45,000 miles per hour, a
mass loss rate equivalent to about one Earth-mass per year, and (perhaps
most significantly) evidence for the influence of magnetic fields in
the collimation and rotation of the material over a scale between about
10-1000 AU. The results add an important link to the chain of evidence
for the role of magnetic fields in influencing the properties of massive
young stars.
