From January 2026 issue
NASA’s IR Space Scope explores the Milky Way’s most abundant star-forming region, revealing new secrets of how stars form.
At near-infrared wavelengths, JWST shows the vast star-forming region Sagittarius B2 filled with young stars and dense clouds of gas and dust that give rise to future stellar generations. Credit: NASA, ESA, CSA, STSCI, A. Ginsberg (University of Florida), N. Budayev (University of Florida), T. Yu (University of Florida)
Giant stars have an enormous impact on their environment and the galaxies they call home. These giants have the highest surface temperatures of any normal star, so they emit abundant ultraviolet radiation that ionizes their surroundings. They also have fierce stellar winds that help shape their gaseous atmospheres. But these monster suns burn their nuclear fuel even faster, so they don’t live long and are therefore extremely rare.
It’s no surprise that astronomers were eager to turn the piercing gaze of the James Webb Space Telescope (JWST) to nearby regions of massive star formation. And what better place to aim than the Sagittarius B2 (Sgr B2) molecular cloud? This vast region of cold gas and dust is the largest and most active star-forming region in our galaxy. It is located a few hundred light years from the supermassive black hole, called Sagittarius A*, which lies at the center of the galaxy.
a milky way champion
At a distance of 27,000 light-years, SGR B2 is close enough to Earth that telescopes can provide a close-up view – just not at optical wavelengths. The dust covering the galaxy’s disk effectively blocks most of the visible light from this region, but the long infrared wavelengths observed by the JWST pass through relatively undamaged. Recent images show SGR B2’s many massive young stars, the hot dust that surrounds them, and more than a dozen previously unseen regions of ionized hydrogen.
“Webb’s powerful infrared instruments provide detail we’ve never been able to see before,” the project’s principal investigator, astronomer Adam Ginsberg of the University of Florida, said in a press release. “This will help us unravel the mysteries of giant star formation and why Sagittarius B2 is so active.”
How active is it? The so-called Central Molecular Zone (CMZ) extends more than 1,500 light years into our galaxy’s core and contains about 80 percent of the galaxy’s dense gas. Yet it makes up only 10 percent of the galaxy’s stars – less than a tenth of what theory suggests. The exception is Sgr B2, which makes up about half of the CMZ’s stars in its 150-light-year-wide volume. It churns out stars at a rate of about 4 solar masses per century, which translates into eight to 10 stars. (No, our galaxy is not a prolific star producer.)
The new images give some clues as to why Sgr B2 looks different. First, the clouds that give rise to the most massive stars appear to be particularly dense, which makes them more resistant to disruption. Second, a sharp boundary at the eastern edge of the cloud (visible at the top left of the images) indicates that a recent event, perhaps the passage of a shockwave from a nearby supernova, triggered the recent process of star formation.
tip of the iceberg
The researchers say their results show that SGR B2 has just begun forming stars. If so, the galaxy’s most active star-forming region has extended its lead to second place. As lead author Nazar Budaev of the University of Florida said, “In everything the Web shows us, there are new secrets to explore.”
Astronomers value every insight the JWST provides into massive star formation for what it reveals not only about the Milky Way, but also about distant galaxies. Studying SGR B2 will help scientists better understand the conditions of galaxies in earlier cosmic times, about 3.5 billion years after the Big Bang, when the rate of star formation peaked.
