The James Webb Space Telescope has unlocked another achievement. This time, the dynamic telescope has peered into the heart of a nearby star-forming region and imaged something astronomers have longed to see: aligned bipolar jets.
JWST observing time is in high demand, and when one group of researchers got their turn, they pointed the infrared telescope at the Serpens Nebula. It’s a young, nearby star-forming region known for being the home of the famous Pillars of Creation. (The Hubble Space Telescope made the pillars famous, and the JWST followed that up with its own stunning image.)
But these researchers weren’t focusing on the Pillars. As a nearby star-forming region, Serpens Nebula is a natural laboratory to study how stars form and to try to answer some outstanding questions about the process. The JWST delivered.
A team of astronomers from the USA, India, and Taiwan examined the region and published their results in a paper titled “Why are (almost) all the protostellar outflows aligned in Serpens Main?” The lead author is Joel Green from the Space Science Telescope Institute.
Stars form when Giant Molecular Clouds of hydrogen collapse. They start out as protostars, objects that haven’t begun fusion yet and are still acquiring mass. As they grow, gas from the cloud gathers in a swirling accretion ring around the star. As it moves, the gas heats up and emits light.
As the cloud collapses into a protostar, some of the energy is converted into angular momentum and the young star spins. For the young star to keep acquiring mass, some of the spin needs to be removed. That happens as the swirling accretion disk emits some of the gas from bipolar jets, also called protostellar outflows. They’re part of how stars regulate themselves as they grow, and they come from the young star’s poles, perpendicular to the spin. The magnetic fields around the star drive the jets out of the poles.
This artist’s illustration shows a young protostar and its protostellar jets. Image Credit: NASA/JPL-Caltech/R. Hurt (SSC)But there’s a lot more detail in the process and some outstanding questions. Stars don’t form in isolation; they usually form in clusters or groups, and there are intermingling magnetic fields at work. At only 1300 light-years away, Serpens Nebula is a good place to try to spy some of this detail. Until the JWST came along, the detail was hidden from even our most powerful telescopes, and astrophysicists were left to theorize with what they could observe.
“Star formation is thought to be partly regulated 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 cloud cores distributed in elongated structures called filaments.”
Cloud cores are the precursors to star clusters, and the filaments are filaments of gas inside giant molecular clouds. Cloud cores cluster along these filaments where the gas density is higher. Much of what goes inside these environments is shrouded by gas and dust, so theories were based on what astronomers were able to observe prior to the JWST.
“While theory often assumes idealized alignment of protostellar disks, cores, and associated magnetic fields, feedback may lead to misalignment on the smallest scales (1000 au) as the protostar evolves,” the authors write. To understand what happens when protostars form in these environments, astrophysicists wanted to know if the angular momentum in a group of stars that form together correlates with each other and with the magnetic field of the filament they form in.
The key to understanding this is the protostellar jets that come from young protostars since their direction is governed by magnetic fields. Protostellar outflows are a signature of young, still-forming stars, and when these outflows collide with the surrounding gas, they create “striking structures of shocked ionized, atomic, and molecular gas,” the authors write.
“Since the jets are likely accelerated and collimated by a rapidly rotating poloidal magnetic field in the inner star-disk system, they emerge along the stellar rotation axis and thus trace the angular momentum vector of the star itself,” the authors explain.
That leads us to the significance of the new JWST image of Serpens Nebula. The researchers found a group of young protostars in the Serpens Nebula with aligned jets. These stars are only about 100,000 years old, making them desirable observational targets in the effort to understand star formation.
This image from the NASA/ESA/CSA James Webb Space Telescope shows a portion of the Serpens Nebula, where astronomers have discovered a grouping of aligned protostellar outflows. These jets are signified by bright, clumpy streaks that appear red, which are shock waves from the jet hitting surrounding gas and dust. Here, the red colour represents the presence of molecular hydrogen and carbon monoxide. Image Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (NASA’s Jet Propulsion Laboratory), J. Green (Space Telescope Science Institute)The jets in a group of young protostars are usually misaligned. Previous research, including research based on JWST images, found only misaligned jets among groups of stars in the same clusters and clouds. Many things can misalign the jets in associated stars, but the outstanding question is if stars that form together start out with the same magnetic field alignment.
Webb found something different in the Serpens Nebula. The telescope found a group of 12 protostars whose jets are lined up with the magnetic field of the filament they formed in.
“The axes of the 12 outflows in the NW region are inconsistent with random orientations and align with the filament direction from NW to SE,” the researchers write in their paper. They say the probability of this happening randomly is extremely low. “We estimate <0.005% probability of the observed alignments if sampled from a uniform distribution in position angle,” they write.
The stars along the filament in the northwest region are aligned, but stars along other filaments in other regions of Serpens are not aligned.
“It appears that star formation proceeded along a magnetically confined filament that set the initial spin for most of the protostars,” the authors write in their conclusion. “We hypothesize that in the NW region, which may be younger, the alignment is preserved, whereas the spin axes have had time to precess or dissociate through dynamic interactions in the SE region.”
The JWST needed only two NIRCam images of the Serpens Nebula to answer a question that’s foundational to star formation. Its work won’t end here.
“We anticipate more detailed studies of star-forming filaments with JWST in the future,” the authors conclude.
