A maelstrom of star formation close to the center of our galaxy has been revealed in two different wavelengths by the James Webb Space Telescope (JWST), its beautiful images highlighting the intensity of star-birth in the region and deepening the mystery of why star formation at the very heart of our galaxy is so sluggish.
Sagittarius B2 is a dense cloud of molecular gas located about 390 light-years from the black hole Sagittarius A* at the center of our Milky Way galaxy. At about 150 light-years across and containing enough gas to assemble 3 million sun-like stars, B2 is the largest, most massive and most active star-forming region in our entire galaxy.
Yet, B2 is at odds with the rest of the galactic center. As massive as B2 is, it contains only 10% of the molecular gas in the galactic center, gas that forms the building blocks of stars. Still, despite only having a modest fraction of gas relative to the galactic center as a whole, B2 produces half of all the stars there. It is an enduring mystery why B2 has such intense star formation while the rest of the galactic center has proportionately lower rates of star-birth.
That’s why the new observations by the JWST are so important in understanding what drives and what puts the brakes on star formation in the galactic center.
“Webb’s powerful infrared instruments provide detail we’ve never been able to see before, which will help us to understand some of the still-elusive mysteries of massive star formation and why Sagittarius B2 is so much more active than the rest of the galactic center,” said study co-author Adam Ginsburg of the University of Florida in a statement.
One theory is that powerful, complex magnetic fields that are entwined around the galactic center and its retinue of molecular clouds similar to B2 could play a deciding factor, but the hows and whys there are still to be determined.
For its part, JWST can get to the heart of the star formation in B2 thanks to the space telescope’s powerful infrared vision that can peer through much of the obscuring dust in the cloud. Presented here are two images, one taken at shorter infrared wavelengths by the JWST’s Near Infrared Camera (NIRCam) and the other captured at longer wavelengths by the telescope’s Mid-Infrared Instrument (MIRI).
In the NIRCam image, we see myriad stars in B2 amid hazy patches of nebulosity. In the darkest areas where we can’t see nebulosity there is cosmic dust too dense even for NIRCam to see through.
So, we turn to MIRI’s image, which is able to penetrate the thicker dust in B2. Here, all but the brightest stars have faded to invisibility since they do not radiate much at these long infrared wavelengths. Meanwhile, the nebulosity across the entire scene has blossomed into life, revealing the true scale of star-birth in the region as each of those bright clouds is being illuminated by the light of very young but massive stars that are still in the process of growing.
The aim of the JWST observations is to better understand the history of star formation in B2. Has it been ongoing for many millions of years and many generations of stars, or has it only recently ignited? The answer will help place B2 into context with the rest of the galactic center as astronomers search for clues as to what stifles star-birth at the heart of our galaxy.
The findings could have broader repercussions. The intensity of star formation in B2 is believed by astronomers to be similar to conditions in the early universe when the first stars were formed in a flurry of frenzied activity. By learning what governs star formation in the galactic center, we could also be learning about what governed star formation in the aftermath of the Big Bang.
A study about these results can be viewed on the paper repository arxiv.