Sagittarius C: James Webb Space Telescope Unveils Magnetic Secrets of the Milky Way’s Heart

Astronomers are finally unveiling the secrets of Sagittarius C with the James Webb Space Telescope (JWST) — and the story is far stranger than anyone expected. New observations and analyses released in 2025 show that this bustling stellar nursery near the Milky Way’s central black hole is being quietly throttled by powerful magnetic fields, reshaping how scientists think stars are born in extreme galactic environments. ^[1]

In a series of papers and coordinated press releases from NASA, ESA, the Space Telescope Science Institute and European research institutes, astronomers have used Webb, South Africa’s MeerKAT radio array and earlier data from ALMA, Spitzer, SOFIA and Herschel to build the most complete picture yet of Sagittarius C — or Sgr C — a dense cloud of gas and dust just a few hundred light‑years from the Milky Way’s central black hole, Sagittarius A. ^[2]

What and where is Sagittarius C?

Sagittarius C is a massive star‑forming cloud embedded in the Central Molecular Zone (CMZ) — the inner few hundred parsecs of the Milky Way, packed with tens of millions of solar masses of dense, turbulent molecular gas. ^[3]

Key facts about Sgr C:

It lies in the direction of the constellation Sagittarius, about 25,000–26,000 light‑years from Earth, near the very center of our galaxy. ^[4]
The cloud itself sits roughly ~200 light‑years from Sagittarius A, the Milky Way’s supermassive black hole of about four million solar masses. ^[5]
Over millions of years, this huge, dense cloud has collapsed in places, forming thousands of young stars and protostars. ^[6]

On paper, this should be one of the Galaxy’s most efficient stellar nurseries. The CMZ harbors some of the densest gas in the Milky Way, and Sgr C is one of its standout clouds. Yet, paradoxically, far fewer stars form there than standard star‑formation laws would predict — a long‑standing puzzle known as star‑formation “suppression” in the galactic center. ^[7]

The 2023 James Webb image that changed everything

The turning point came on 20 November 2023, when NASA and ESA released Webb’s first high‑resolution near‑infrared image of Sagittarius C, taken with the NIRCam instrument in September 2023. ^[8]

That image revealed:

A 44–50 light‑year‑wide swath of the Milky Way’s dense center. ^[9]
An estimated 500,000 stars shining through the dust — everything from massive newborns to older populations in the background. ^[10]
A huge region of ionized hydrogen wrapping around an infrared‑dark cloud — a super‑dense clump of dust that blocks the starlight behind it. ^[11]
A cluster of protostars buried at the base of that dark cloud, their outflows lighting up the gas “like a bonfire” in the middle of the shadowed region. ^[12]
Dozens of thin, needle‑like structures in the ionized gas, whose strange geometry immediately caught astronomers’ attention. ^[13]

Webb’s sensitivity and sharp vision at infrared wavelengths allowed astronomers to peer through the obscuring dust with unprecedented clarity. As one of the principal investigators put it in NASA’s 2023 release, this region had never been seen in such detail before, and many of its features were completely new to science. ^[14]

At the time, researchers knew they had something special. They also knew the snapshot raised more questions than it answered.

2025: Protostars, jets and a hidden cloud revealed

Those questions drove a deeper investigation. In April 2025, teams led from the University of Virginia, the University of Colorado Boulder and the Instituto de Astrofísica de Andalucía published two companion papers in The Astrophysical Journal:

The JWST‑NIRCam View of Sagittarius C. I. Massive Star Formation and Protostellar Outflows ^[15]
The JWST‑NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the Central Molecular Zone ^[16]

These studies, along with a NASA press release and institutional updates from Spain and Colorado, turned the pretty picture into a fully fledged physical story. ^[17]

Massive baby stars in an extreme nursery

By combining Webb data with earlier observations from ALMA, Spitzer, SOFIA and Herschel, the team dissected the brightest cluster in Sagittarius C. They found: ^[18]

Two very massive protostars, each already around 20 times the mass of the Sun, still wrapped in envelopes of roughly 100 solar masses of gas and dust.
Bright, collimated outflows (jets) blasting out from these giants, now clearly visible in infrared for the first time in this region.
Dozens of lower‑mass protostars, identified by matching Webb’s infrared detections to compact dust cores previously mapped by ALMA.
At least 88 knots of shocked hydrogen gas, where jets slam into the surrounding cloud, traced in Webb’s narrow‑band imaging.

One of the surprises was the discovery of a previously unknown star‑forming pocket within Sgr C, hosting a high‑mass protostar of ~9 solar masses embedded in a massive dust core and associated with strong water maser emission — a classic sign of vigorous, ongoing star formation. ^[19]

In Spanish researchers’ summary, the region shows more than a hundred detected jets from low‑mass protostars, plus the first infrared detection of jets from these two massive stars — clear evidence that, despite the hostile conditions, the basic physics of star formation looks surprisingly familiar to what we see in calmer nurseries like the Orion Nebula. ^[20]

Magnetic fields that choke off star birth

If Sagittarius C has plenty of gas and is clearly forming stars, why is the overall star‑formation rate in the CMZ so low? That is where the second paper — and the most visually striking feature of the Webb images — comes in.

Filaments that trace invisible forces

Webb’s 4.05‑micron Brackett‑α images show that the ionized gas in Sgr C is dominated by bright filaments, many stretching over several light‑years and forming a broken, π‑shaped arc around the central molecular clump, with fainter strands radiating outward. ^[21]

When astronomers compared Webb’s view to:

MeerKAT radio data spanning 1,000 light‑years across the galactic center, and
ALMA radio observations at higher frequencies,

they found that these filaments emit a mix of thermal and non‑thermal radio emission, and that their shapes and brightness changes are consistent with plasma confined and guided by strong magnetic fields. ^[22]

In technical terms, the plasma in Sgr C’s H II region appears to be magnetically dominated, with a plasma β (thermal pressure divided by magnetic pressure) less than one — meaning magnetic forces outweigh gas pressure in controlling the flow. ^[23]

A magnetic brake on star formation

Taken together, Webb’s filaments and the radio data point to a clear picture:

Gas spiraling in the strong gravitational and tidal field of Sagittarius A stretches and amplifies ambient magnetic fields near the galactic center. ^[24]
Those enhanced magnetic fields thread the gas in Sgr C, confining hot plasma into narrow filaments and arcs rather than letting it expand freely. ^[25]
Crucially, the same fields likely resist the gravitational collapse of dense molecular clouds, acting as a kind of magnetic “scaffolding” that slows or even prevents the gas from forming new stars. ^[26]

This is the leading explanation for why Sagittarius C — and the CMZ as a whole — produces fewer stars than expected, even though the region is packed with gas that, in other parts of the galaxy, would be explosively star‑forming. ^[27]

One of the study’s authors has even suggested that most mature H II regions in the CMZ, and perhaps in many galactic nuclei, evolve in this magnetically dominated regime, implying that magnetic suppression of star formation may be a common feature near galaxy centers. ^[28]

A stellar nursery near the end of its life

Despite the hypnotic beauty of the Webb images, Sagittarius C itself appears to be in its later stages as a star‑forming cloud.

According to the 2025 analyses:

The young stars it has already produced are blowing away the remaining molecular gas with radiation and stellar winds.
Over the next few hundred thousand years, the cloud’s dense reservoir may disperse altogether, effectively shutting down further star formation in this particular nursery. ^[29]

In that sense, astronomers are catching Sgr C “before the end credits roll” — a final, detailed look at how a massive stellar nursery lives, forms stars, and ultimately destroys the very cloud that birthed it.

How Sagittarius C compares to other star‑forming regions

To appreciate how extreme Sagittarius C is, it helps to compare it with other well‑known nurseries.

Orion vs. the galactic center

The Orion Nebula, a favorite of backyard telescopes, is a relatively nearby and “normal” star‑forming region. Its gas appears comparatively smooth in infrared images, and magnetic fields, while present, don’t carve the same kind of dramatic filament network seen in Sgr C. ^[30]

Researchers argue that the difference comes down largely to environment: Orion lives in the Milky Way’s calm disk, far from the maelstrom around the central black hole, while Sagittarius C is marinating in: ^[31]

Much denser and hotter gas
Stronger turbulence and cosmic‑ray flux
Far more intense UV and X‑ray radiation
Stronger, more tangled magnetic fields

Sagittarius B2: The overachieving neighbor

Only a few hundred light‑years away within the CMZ, Sagittarius B2 (Sgr B2) tells the opposite story. Recent Webb images of Sgr B2 show a gargantuan, dust‑rich cloud that holds only around 10% of the region’s gas but seems to power roughly half of the star‑formation activity near the galactic center. ^[32]

Where Sagittarius C is comparatively under‑productive, Sagittarius B2 is a star‑formation powerhouse, underscoring that the CMZ is anything but uniform — and hinting that local conditions, including magnetic field geometry and cloud history, play a huge role in determining whether gas becomes stars or remains stalled.

A multi‑wavelength view of the Milky Way’s core

One of the most striking aspects of the new Sagittarius C results is how different telescopes and wavelengths come together:

JWST (near‑infrared) sees embedded stars, protostars, ionized gas and dust structures with exquisite detail. ^[33]
MeerKAT (radio) reveals extended vertical filaments and shells across a 1,000‑light‑year stretch of the galactic center, putting Sgr C’s Webb field — just 44 light‑years wide — into context. ^[34]
ALMA and other radio observatories trace dense cores, jets and non‑thermal emission from relativistic electrons spiraling along magnetic field lines. ^[35]

Together, they paint a picture of a dynamic, magnetized ecosystem around Sagittarius A, where gas flows, explodes, collapses and sometimes stubbornly refuses to form stars.

Those insights dovetail with separate JWST observations of Sagittarius A* itself, which show the accretion region flickering constantly with flares and turbulent emission over timescales of hours to days. ^[36] The result is a unified, evolving view of the Milky Way’s core — from the black hole’s immediate surroundings out into star‑forming clouds like Sgr C and Sgr B2.

Why Sagittarius C matters far beyond our own galaxy

Studying Sagittarius C isn’t just about understanding one cloud; it’s about testing the physics of star formation and feedback in galactic nuclei in a laboratory we can resolve star by star.

The new JWST‑driven picture has several big implications: ^[37]

Magnetic fields matter more than we thought
Many galaxy‑evolution models focus on gravity, turbulence and radiation feedback. Sgr C shows that strong magnetic fields can rival or exceed these in regulating how efficiently gas turns into stars, especially near supermassive black holes.
Galactic centers can self‑regulate star formation
If magnetic fields amplified by black‑hole‑driven dynamics can suppress star formation, then central regions of galaxies may naturally cycle between active, star‑bursting phases and quieter, magnetically “locked” periods.
Other galaxies likely hide similar magnetized nurseries
The authors of the magnetically dominated H II‑region study argue that what’s seen in Sgr C may be common across other galactic nuclei — we just can’t resolve them as clearly as in our own Milky Way. JWST observations of nearby galaxy centers will be a crucial test.

What’s next for Webb and the galactic center?

The story of Sagittarius C is still unfolding. Looking ahead, astronomers plan to: ^[38]

Use future JWST cycles to image other CMZ clouds, testing whether the same filament‑rich, magnetically dominated structures appear elsewhere.
Combine MeerKAT and upcoming Square Kilometre Array (SKA) data for even more precise maps of the magnetic fields threading the galactic center.
Extend detailed modeling of star‑formation suppression to galaxy centers beyond the Milky Way, checking whether similar mechanisms can explain puzzlingly low star‑formation rates observed in some galactic nuclei.

For now, though, Sagittarius C stands as a showcase of what the James Webb Space Telescope was built to do: turn breathtaking images into hard physics, revealing that the heart of our galaxy is not just beautiful, but governed by invisible forces powerful enough to sculpt stars themselves.

James Webb Reveals Milky Way’s Biggest Star Factory | Sagittarius B2