“Webb” looked into the heart of the star-forming region

The James Webb Space Telescope has achieved another success. This time, the tireless telescope peered into the heart of a nearby star-forming region and captured an image of something astronomers have long wanted to see: aligned bipolar jets.

Webb's observing time is in high demand, and when one team of researchers had their turn, they pointed the infrared telescope at the Serpent Nebula. It's a young, nearby star-forming region known for containing the famous Pillars of Creation. (The Hubble Space Telescope made the Pillars famous, and Webb followed suit with its own stunning image).

But these researchers did not focus on the Pillars. The Serpent Nebula, a nearby star-forming region, is a natural laboratory for studying star formation and trying to answer some of the outstanding questions about the process. Webb coped with this task.

A team of astronomers from the United States, India and Taiwan explored this region and published their results in a paper entitled “Why are (almost) all protostellar streams aligned in the main part of the Serpentine Nebula?” Lead author is Joel Green of the Space Telescope Science Institute.

Stars form when giant molecular clouds of hydrogen collapse. They first become protostars — objects that have not yet begun thermonuclear fusion and continue to gain mass. As they grow, gas from the cloud gathers into a rotating accretion ring around the star. As the gas moves, it heats up and emits light.

When the cloud collapses into a protostar, some of the energy is converted into angular momentum, and the young star begins to rotate. In order for the young star to continue to gain mass, some of the rotational energy must be removed. This occurs when the rotating accretion disk ejects some of the gas from bipolar jets, also called protostellar outflows. With their help, stars regulate their growth process, and emanate from the poles of the young star, perpendicular to the spin. Magnetic fields around the star direct the jets away from the poles.

But there are still many details and unresolved issues in this process. Stars do not form alone; They usually form in clusters or groups and are subject to interlocking magnetic fields. The Serpent Nebula, located just 1,300 light-years away, is a great place to try to discern some of these features. Until Webb came along, these details were hidden from even the most powerful telescopes, leaving astrophysicists to theorize based on what they could observe.

“Star formation is thought to be partly controlled by magnetic fields with coherence scales of a few parsecs — smaller than giant molecular clouds but larger than individual protostars,” the authors write in their paper. “Magnetic fields likely play a key role in the collapse of the cloud cores, which are distributed into elongated structures called filaments.”

Cloud cores are the precursors of star clusters, and filaments are strands of gas within giant molecular clouds. Cloud cores cluster along these filaments, where gas density is higher. Much of what happens inside these environments is shrouded in gas and dust, so theories were based on what astronomers could observe before Webb arrived.

“Although theory often assumes an idealized alignment of protostellar disks, cores, and associated magnetic fields, feedback can lead to misalignment on very small scales (1,000 AU) as the protostar evolves,” the authors write. To understand what happens when protostars form under such conditions, the astrophysicists wanted to know whether the angular momentum in a group of stars that form together correlates with each other and with the magnetic field of the filament in which they form.

The key to understanding this is the protostellar jets that come from young protostars, as their direction is controlled by the magnetic field. Protostellar jets are a characteristic feature of young, still-forming stars, and when these jets collide with surrounding gas, they create “striking structures of impact-ionized, atomic and molecular gas,” the authors write.

“Because the jets are likely accelerated and collimated by the rapidly rotating poloidal magnetic field in the inner star-disk system, they emerge along the rotation axis of the star and thus track the angular momentum vector of the star itself,” the authors explain.

This brings us to the significance of Webb's new image of the Serpent Nebula. The researchers found a cluster of young protostars with aligned jets in the Serpent Nebula. These stars are only about 100,000 years old, making them desirable targets for understanding how stars form.

Jets in a group of young protostars are usually displaced. Previous studies, including those based on Webb images, have found only discordant jets in groups of stars in the same clusters and clouds. The jets of associated stars can be misaligned for many reasons, but the question remains whether stars that form together start out with the same magnetic field alignment.

In the Serpens Nebula, Webb discovered something different. The telescope discovered a group of 12 protostars whose jets were aligned with the magnetic field of the filament in which they formed.

“The axes of the 12 jets in the NW region are not randomly oriented and are aligned with the NW-SE filament direction,” the researchers wrote in their paper. They say the probability of this happening by chance is extremely low. “We estimate a <0.005% probability of the observed alignments if the sample is drawn from a uniform position angle distribution," they wrote.

The stars along the filament in the northwest region are aligned, but the stars along other filaments in other regions of Serpens are not aligned.

“It appears that star formation occurred along a magnetically confined filament that set the initial rotation for most protostars,” the authors write in their conclusion. “We suggest that in the northern region, which may be younger, the alignment was preserved, while the spin axes precessed or diverged as a result of dynamical interactions in the southern region.”

Webb needed just two NIRCam images of the Serpentine Nebula to answer a question fundamental to star formation. His work will not end there.

“We look forward to more detailed studies of star-forming filaments using Webb in the future,” the authors conclude.