It Takes Two

A very nice study was announced last week showing an environment where planets may be forming around a very young binary star system.  The object in question is called “SVS13” and it resides in the Perseus molecular cloud about 1,000 lightyears from the Sun.  In this case, the two previously known young binary objects are separated by a distance about 90 times that between the Earth and the Sun, giving it an orbital period of about 850 years.   Interestingly, the two protostars can’t be seen in optical light because they are so enshrouded by dust in their common birth cocoon that they are only detectable at high frequency radio waves.  In this new study, the team used ALMA and VLA data to explore the pair’s circumbinary environment, and amazingly they find that each protostar is surrounded by its own disk and the pair appears to be surrounded again by a circumbinary disk.  Also, this latter disk seems to have some rather well-defined spiral arm features, possibly resulting from the periodic gravitational tugs of the two protostars as they orbit each other in the middle. 

I’ve attached a picture of the spiral structure to this post, which has been specifically altered in the right panel to highlight features in the image with greater distance from the binary pair seen in the middle.  (In this image, low brightness has been colour coded blue, while high brightness has been coded as red, or white for the brightest fluxes.)  Two or maybe even three curved structures can be plainly seen.  Meanwhile, it’s possible that planets will eventually form in either the circumstellar or circumbinary gas in this system, should localized areas  in these structures produce the seeds that grow as surrounding mass is drawn toward them.  The team doesn’t see any features in the disks that suggest a particular protoplanet but perhaps further data at even higher resolution will be revelatory in that regard.  Meanwhile, here are links to the press release and the arXiv preprint for those who’d like more information.  (See the press release for a nice illustration of how this system is configured.)

Next, it appears that the sharp rise in brightness in the young star EX Lupi that I described yesterday was short-lived after all.  Doug reported later (which I read only after posting yesterday’s message – d’oh!) that the star dropped in brightness for two nights in a row over the weekend, suggesting what its noted increase was only due to a small localized burst in its disk and not the start of a major, disk-wide event.  Oh well!  The team will undoubtedly continue to monitor several young stars for future accretion events.