Magnetic Winds from a Young Star
Thursday, June 27, 2013
Science Update - A look at CfA discoveries from recent journals

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 the nebula and all of its clusters very well. Some contain dramatic outflows of material, for example, that may be driven by a single star or perhaps by a whole cluster. One reason for this ignorance is because the nebula is so crowded with stars, not to mention that dust obscures many of its regions from optical view.

On the far side of the optical nebula is a second nursery of still younger stars that can only be detected in infrared light because the intervening dust absorbs optical light. Astronomers have argued for decades about how to account for the enormous luminosity of this region, equal to about 100,000 suns, and what drives outflows of gas seen near its obscured center. One contributor to the outflow is an enigmatic object known as Radio Source I, apparently composed of two stars each about ten times more massive than the Sun and separated by a distance only a few times that of the Earth's orbit. Orbiting the stars is a disk of hot gas (smaller in dimensions than our solar system), and a strong wind blowing towards the poles.

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
tracking minute motions of bright spots in the outflowing gas. They found that the gas appears to spin around the polar axis in the same sense as the remnant disk, and what's more, the gas becomes focused downstream where there is no obvious confining material. The astronomers argue that rotation of the outflow and the change in its shape is evidence for magnetic fields emanating from the disk and wound into a helix-like configuration by the rotation. The fields could regulate the dynamics of gas with few other outward signs. While magnetic fields are widely believed to have a significant role in regulating how Sun-like stars form, the present study offers the first direct evidence that magnetic fields play a role in formation of very massive stars.