A Spider-Like Outflow in a Young Star Forming Region
Friday, July 4, 2014
Science Update - A look at CfA discoveries from recent journals

Astronomers in the past decade have been able to examine some of the key physical processes underway in early stages of stellar gestation, thanks in part to submillimeter and infrared telescopes that can peer through the heavy obscuration of dust in the birth clouds. One of the key current mysteries is how new stars rid themselves of the spin that has accumulated as material in the cloud contracted to form them. The answer is probably lies in the bipolar jets of material observed shooting from the stars. These jets can channel the spinning material into outflows that escape and allow the contraction to continue. Indeed these outflows, often dramatically narrow and long, are commonly seen. How and when these flows develop, and how effective are they at enabling a young star to continue its growth, remain key areas of research.

The leading theories on the origin of protostellar outflows suggest that they are generated through the interaction of ionized material in the star’s disk and the magnetic fields present in the star and/or the disc. Protostellar winds then entrain the host cloud’s molecular gas, thereby producing molecular outflows. There is substantial observational evidence showing that molecular outflows from low-mass young stars tend to have relatively well collimated lobes early in their development but that they tend to develop wider opening angle flows at later stages. There is, however, no consensus on the detailed physics that produces this evolutionary trend in molecular outflows: a wandering jet axis (precession) could for example produce wider cavities as the protostar evolves. Alternatively, protostellar winds could have both collimated and wide-angle components whose relative strengths vary with age.

CfA astronomers Erin Brassfield and Nimesh Patel, along with four colleagues, used the Submillimeter Array to study the outflow in the stellar nursery known as Barnard-5, located about 790 light-years away. The find that the flow actually has multiple arms with a spider-like complexity, and includes both narrow jets as well as a wide-angle component, with different velocity gas present in each arm. They are able for the first time to reveal the presence of intermediate speed shells of material emerging from close to the star as well as some bullet-like ejecta probably associated with the narrow jet. The new results are consistent with the view that young outflows have multiple components that evolve in relative importance with time, this particular source being observed in a unique, transitional stage between highly collimated activity and a wider-angle wind.

Reference(s): 

"A Spider-Like Outflow in Barnard 5 - IRS 1: The Transition from a Collimated Jet to a Wide-Angle Outflow?," Luis A. Zapata, Hector G. Arce, Erin Brassfield, Aina Palau, Nimesh Patel, and Jaime E. Pineda, MNRAS, 441, 3696, 2014.