Weekly Science Update

Friday, October 17, 2008
Double Jets in Young Binary Stars
Most stars the size of the sun or larger (in mass) are part of multiple stellar systems in which two or even three stars orbit around one another. This tendency presumably reflects the conditions that existed when stars were born, since it is unlikely that stars pair up later on in their lives. The local conditions during star formation in turn reveal the complex environments when planets (if there are any) form around these stars. Binary stars might tend to disrupt the formation of any planets around them, for example.

Star birth is typically accompanied by the production of narrow bipolar jets of gas that shoot out perpendicular to the (possibly protoplanetary) disks around the young stars. These jets of material provide important diagnostics of the young stars and their environments, and multiple stars should, it is thought, have multiple jets. But although multiplicity is common in young stellar nurseries, it has been extremely difficult to study multiple jets in such systems -- very high spatial resolution millimeter (or submillimeter) wavelength studies are necessary to disentangle the multiple streams of gas.

The Submillimeter Array (SMA) is uniquely capable of making just such precise spatial measurements of jets, and a team of two SAO astronomers, Xuepeng Chen and Tyler Bourke, along with two colleagues, have now done so. They studied a young binary system about 1200 light-years away; the two stars are separated by about 8700 astronomical units (one AU is equivalent to the average distance of the earth from the sun). Writing in last week's Astrophysical Journal Letters, the team reports mapping two jets, one from each star. They find that the jets are nearly perpendicular to each other, with the two flows apparently independent of each other. They also find that the more massive star in the pair has the more massive outflow, perhaps because it has a more massive disk that helps generate the outflow. Equally interesting, their results demonstrate that jets in binaries -- and so protostellar disks -- are not necessarily co-aligned with each other after the binary stars are produced. Why this should happen remains one of the important questions to be studied in future research.


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