Webb provides closest look yet at one of Milky Way’s most extreme environments

Sagittarius C is one of the most extreme environments in the Milky Way galaxy. This cloudy region of space sits about 200 light-years from the supermassive black hole at the center of our galaxy. Here, a massive and dense cloud of interstellar gas and dust has collapsed on itself over millions of years to form thousands of new stars.

In a new study, a team of scientists used observations from NASA’s James Webb Space Telescope to study Sagittarius C in unprecedented detail. The research was led by University of Colorado Boulder astrophysicist John Bally, Samuel Crowe at the University of Virginia, Rubén Fedriani at the Instituto de Astrofísica de Andalucía in Granada and their colleagues.

The findings could help solve a long-running mystery about the innermost stretches of the galaxy, or what scientists call the Central Molecular Zone (CMZ): The region hosts high densities of interstellar gas. So why are fewer new stars born here than scientists once predicted?

The researchers discovered that powerful magnetic field lines seem to be threading through Sagittarius C, forming long and bright filaments of hot hydrogen gas that look a little like spaghetti noodles—a phenomenon that could slow down the pace of star formation in the surrounding gas.

“It’s in a part of the galaxy with the highest density of stars and massive, dense clouds of hydrogen, helium and organic molecules,” said Bally, professor in the Department of Astrophysical and Planetary Sciences at CU Boulder. “It’s one of the closest regions we know of that has extreme conditions similar to those in the young universe.”

He and his colleagues published their findings April 2 in The Astrophysical Journal. The research is part of an observation campaign proposed and led by Crowe, a fourth-year undergraduate student at the University of Virginia who was recently named a Rhodes Scholar.

And, Crowe noted, the Webb telescope’s startling images show Sagittarius C as it’s never been seen before.

“Because of these magnetic fields, Sagittarius C has a fundamentally different shape, a different look than any other star forming region in the galaxy away from the galactic center,” Crowe said.

Stellar nurseries

The research sheds light on the violent births and deaths of stars in the Milky Way galaxy.

Stars tend to form within what scientists call “molecular clouds,” or regions of space containing dense clouds of gas and dust. The closest such stellar nursery to Earth lies in the Orion Nebula, just below Orion’s belt. There, molecular clouds have collapsed over millions of years, forming a cluster of new stars.

Such active sites of star formation also spell their own demise. As new stars grow, they begin to emit vast amounts of radiation into space. That radiation, in turn, blows away the surrounding cloud, stripping the region of the matter it needs to build more new stars.

“Even the sun, we think, formed in a massive cluster like this,” Bally said. “Over billions of years, all of our sibling stars have drifted away.”

In a separate study published today in the same journal, Crowe and his colleagues, including Bally, dove into the growing “protostars” forming in Sagittarius. Their data reveal a detailed picture of how these young stars eject radiation and blow away the gas and dust around them.

Magnetic fields

In his study, Bally explored Sagittarius C’s unusual appearance. He explained that while the Orion Nebula looks mostly smooth, Sagittarius C is anything but. Weaving in and out of this region are dozens of bright filaments, some several light-years long. These filaments are made up of plasma, a hot gas of charged particles.

“We were definitely not expecting those filaments,” said Rubén Fedriani, a co-author of the study and postdoctoral researcher at the Instituto de Astrofísica de Andalucía in Spain. “It was a completely serendipitous discovery.”

Bally noted that the secret to Sagittarius C’s filaments, and the nature of its star formation, likely comes down to magnetic fields.

A supermassive black hole with a mass about four million times greater than our sun sits at the center of the galaxy. The motion of gas swirling around this behemoth can stretch and amplify the surrounding magnetic fields. Those fields, in turn, shape the plasma in Sagittarius C.

Bally suspects that the Orion Nebula looks much smoother because it resides within a much weaker magnetic environment.

Scientists, he added, have long known that the galaxy’s innermost regions are an important birthplace for new stars. But some calculations have suggested that the region should be producing a lot more young stars than observed. In the CMZ, magnetic forces may be strong enough to resist the gravitational collapse of molecular clouds, limiting the rate of new star formation.

Regardless, Sagittarius C’s own time may be drawing to a close. The region’s stars have blown away much of its molecular cloud already, and that nursery could disappear entirely in a few hundred thousand years.

“It’s almost the end of the story,” Bally said.