Twisting in the Wind
A false color infrared image of the NGC 2264 G outflow (the green filamentary structure) taken by the Infrared Array Camera. The jet extends over 4 light-years in length, and its shape suggests that the star of origin (labeled VLA2) is slowly precessing. The axes label the spatial position of the object.
The process of star formation, once thought to involve just the simple coalescence of material under the influence of gravity, is now known to incorporate an exceedingly complex series of processes. Newly forming stars are often seen assembling circumstellar disks (possibly preplanetary in nature) while at the same time ejecting dramatic outflows of material in the form of jets blown outward in opposing directions perpendicular to such disks. These winds and outflows are significant because they disrupt the young star's environment, although how severely is still not clear.
Sometimes these outflows are narrowly collimated, but in other cases they are wide-angled flows, and, to make things even more confusing, the flows are often twisted or bent. A number of suggestions have been put forward to explain these features, and all of them carry implications about the star and its developing disk. A new paper by SAO astronomers Paola Teixeira and Charlie Lada and two colleagues considers five such options in the case of one prominent outflow that stretches and twists across its length of over four light-years: side winds or overlapping flows, magnetic forces, precession of the star ejecting the jet (perhaps due to the presence of a nearby star), deflection by knots in the interstellar medium, or motion of the stellar source perpendicular to the flow.
The scientists analyzed images of the jet obtained with the Infrared Array Camera on the Spitzer Space Telescope, images that clearly showed the shape of the entire jet as well as the locations of embedded knots of material and subsidiary structures. In particular, the team reports identifying the young star responsible for the flow (a star that had been obscured in the visible by its surrounding natal dust cloud).
After a careful analysis, the team concludes that the most probable cause for the outflow shape is the precession of the driving star; they derive a characteristic period of about 8000 years, consistent with other timescales derived for the young region. They caution, however, that some aspects of the shape seem to require a secondary role for one or more of the other scenario mechanisms. The results help to quantify the behavior of outflows around young stars, and demonstrate that protoplanetary disks or other structures in stellar nurseries are susceptible to a variety of disruptive phenomena.