Mystery in the Orion Nebula
Thursday, June 11, 2009
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. In fact, the nebula's bright glow comes from gas and dust that are illuminated by the intense ultraviolet radiation from these stars. The nebula is about 1300 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 quite 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, but in the last decade astronomers found that this source was itself comprised of several smaller ones. It turns out that one of these objects, an intense radio source called "Source I," is the dominant young star in the region, and an enigmatic one at that. Its motions suggest that it was ejected from another system just a few hundred years ago; other evidence suggests it is surrounded by natural masers (radio wavelength analogues
of lasers) that lie in a circumstellar disk of material. Such masers typically signal dense material around young stars.

CfA astronomers Ciriaco Goddi, Lincoln Greenhill, Liz Humphries, and Lynn Matthews, together with two colleagues, have used very high angular resolution radio images,
to probe the activity around Source I. By studying several isotopes of the molecular gas in the region they are able to confirm for the first time that masers are indeed present. Moreover, they can attribute the outflow to a complex bipolar structure, and trace it to its origin in a region very close to Source I roughly comparable in size to that of our solar system. Some modeling remains to be completed, but the results so far go a long way towards figuring out what is going on in at least this region of the Orion Nebula, and offering clues about similar activity elsewhere in young stellar clusters.