Star-forming cloud Sagittarius B2 explored with JWST

Using the James Webb Space Telescope (JWST), astronomers from the University of Florida and elsewhere have performed infrared observations of a star-forming cloud known as Sagittarius B2. Results of the observational campaign, published September 15 on the arXiv preprint server, provide important insights into the properties of this cloud.

Sagittarius B2 is a star-forming cloud in the Milky Way, located some 27,000 light years away and 330 light years away in projection from the galactic center. The cloud is forming stars at a rate of 0.04 solar masses per year, which makes it one of the most active sites of star formation in our galaxy.

Previous observations of Sagittarius B2 have found that it contains over 700 young stellar objects (YSOs), over 50 regions of ionized atomic hydrogen (H II regions), many outflows, dozens of hot cores, and hundreds of masers. More recently, a team of astronomers led by University of Florida’s Nazar Budaiev decided to take a closer look at Sagittarius B2 using JWST’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

“We presented JWST’s NIRCam and MIRI first view of the most vigorously star forming cloud in the CMZ [Central Molecular Zone], Sagittarius B2,” the researchers write.

JWST observations found that Sagittarius B2 has a very structured morphology. While the earliest stages of star formation are present in the western side of the cloud as seen by previous observations, JWST detected recent star formation in the eastern, less dense part of the cloud. One region of Sagittarius B2 is seen being backlit by extended recombination line emission showing a sharp cloud edge on one side.

The observations revealed that Sagittarius B2 contains both a revealed low-extinction and hidden high-extinction population of massive stars. Moreover, by analyzing JWST imaging, the astronomers identified new candidate H II regions around massive stars previously missed by radio telescopes.

MIRI allowed the team to find that radiation is escaping from one of the star-forming regions in the cloud, designated Sgr B2 N, along its outflow cavities. This finding shows that infrared photons do not get trapped within dense clusters, but can find geometric escape routes even in the densest, most heavily embedded regions in the universe.

The astronomers noted that although JWST observations had high sensitivity, they were not able to detect an extended population of YSOs in Sagittarius B2. This, according to the scientists, suggests that star formation has only just begun in the cloud.

The authors of the paper concluded that their study underscores the capabilities of JWST instruments regarding star formation in extreme environments.

“JWST unveils previously hidden massive stars and ionized structures, offering a transformative view of how stars form under some of the most extreme galactic conditions,” the researchers conclude.

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