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Webb’s Star Formation Discoveries

Identifying what’s in molecular clouds and detailing stars in the process of forming.

In just two years, the James Webb Space Telescope has delivered invaluable details that are reshaping researchers’ understanding of how young stars form. It has identified ices and many other complex organic molecules in the clouds where stars begin gathering mass. This includes new details about their histories of gobbling up and ejecting material. Webb has also pinpointed clear evidence of how water begins as ice and becomes vapor as it travels closer to a young star, creating a rich environment where Earth-like planets may take shape.

In This Article:

How Do Stars Form?

Stars form in super cold environments, known as molecular clouds over millions of years. These clouds are as cold as 10 kelvin (negative 260 Celsius or negative 440 Fahrenheit), and are filled with gas and dust. Denser areas of these clouds collapse gravitationally into clumps, which then collapse into many cores. Those cores further collapse into individual protostars. As they form, protostars will continue to pull in surrounding gas. Some molecular clouds are dominated by massive stars, and others have a greater number of smaller stars.

Video: Exploring Star and Planet Formation

This animation explores the stages in the formation of stars and planets. Within a large, dense cloud, thousands of protostars collapse due to gravity. The infalling material forms a disk around the protostar, with jets emitted perpendicular to the disk. Planets condense and build up within the disk, establishing a new solar system. The Webb Space Telescope’s infrared observations will peer into these dark clouds and dusty disks to examine this formation process with unprecedented clarity.
Video: NASA, ESA, CSA, STScI; Animation: Dani Player (STScI), Frank Summers (STScI); Audio: Joseph DePasquale (STScI)

Download the video captions (VTT), and transcript of the audio description (Word Doc, 19 KB).

Let’s consider the “heavyweights” first. Massive young stars form and accumulate their mass over tens of thousands of years. As they take shape, these stars inject an incredible amount of energy into their environments. For example, massive stars send out stellar winds and emit ultraviolet light, which disrupt the bulk of the surrounding molecular cloud and limit how many other stars — and planets — can form near them. The reverse is also true: These same processes can compact surrounding dense gas, and can trigger new star formation.

In contrast, smaller young stars (like our Sun once was) form more slowly, over a few million years. During this process, smaller stars periodically shoot out jets and outflows, but do not influence their local environments as significantly as massive stars. Over time, a flattened circumstellar disk forms around these smaller stars, where planets may eventually take shape.

Analyzing the Contents of Molecular Clouds

Stars form in molecular clouds that are seeded with dust grains, elements, and molecules that may end up in the stars themselves — or near them, where planets may eventually form. Thanks to Webb’s sensitive near- and mid-infrared instruments, researchers can now better identify materials that exist in molecular clouds and the stars within them.

A black background is filled with pinpoints of light, which are distant galaxies, in different shades of red, orange, and blue. In the foreground and taking up most of the image are blue, smoky, translucent wisps. They begin at bottom left and make their way through the center before going out toward the top. On the left top side, some of the wisps are orange and white. Below them are four bright points of light, which are stars. Three are orange, and the one at far left appears orange-white. The stars have Webb’s signature 8-point diffraction spikes, which are also orange.
Webb’s near-infrared image of the central region of the Chamaeleon I molecular cloud features cold, wispy cloud material in blue. Astronomers studying this molecular cloud discovered diverse ices in the darkest regions measured to date. Learn more about what they found.
Image: NASA, ESA, CSA; Science: IceAge ERS Team, Fengwu Sun (Steward Observatory), Zak Smith (The Open University); Image Processing: Mahdi Zamani (ESA/Webb)
Graphic titled "NGC 1333 IRAS 2A Protostar, MIRI Medium-Resolution Spectroscopy" shows a graph of optical depth versus wavelength from 6.8 to 8.6 microns, with a variety of molecules highlighted.
In another location, NGC 1333 IRAS 2A, Webb detected a wealth of complex, carbon-containing molecules surrounding two protostars, including acetaldehyde, ethanol, and methyl formate in mid-infrared light. These and other molecules detected by Webb represent key ingredients for making potentially habitable worlds. Read more about what researchers identified.
Illustration: NASA, ESA, CSA, Leah Hustak (STScI)

In the Chamaeleon I molecular cloud, Webb obtained an in-depth inventory of the deepest, coldest ices measured to date in any molecular cloud. The telescope identified simple ices like water, along with frozen forms of a wide range of molecules, from carbonyl sulfide, ammonia, and methane to the simplest complex organic molecule, methanol. These detections are crucial, since ices are vital ingredients for habitable planets and are the main sources of several key elements, including carbon, hydrogen, oxygen, nitrogen, and sulfur.

Studying Individual Young Stars in Detail

Researchers using Webb found new evidence of the growth cycles of smaller stars, including the shape and history of their ejections. First up: Webb’s tight view of the protostar within the molecular cloud L1527. Observations were taken in two types of light, near-infrared and mid-infrared, which revealed the star’s once-hidden features, like its past outbursts that form an hourglass shape. Look first at the dark regions that form a rough bowtie shape along the sides of the bright hourglass, and the small edge-on disk at the center. These darker areas are remnants of the molecular cloud that led to the star’s formation, and they block light from distant stars and galaxies. Now, focus on the center and the brightly lit regions: As the forming star gathers mass from the disk, it also ejects some material in outflows. The star’s light shines through these areas.

Not all ejections are alike. Sometimes, a star builds mass in periodic bursts, and later “burps” or ejects material. This star’s activities are also visible in these outflows — look for bubble-like shapes. Not only can researchers use the shapes of the outflows to trace the history of the star’s activity, they can also search for specific molecules and elements throughout the scene.

Two views of the same object, a forming protostar surrounded by a large hourglass-shaped nebula known as L1527. Webb’s near-infrared image is at left, and its mid-infrared image is at right. The hourglass is slightly larger in near-infrared. Click View Description for more information.
Webb captured the protostar within the molecular cloud L1527 in near-infrared light, at left, and mid-infrared light, at right. Near-infrared shows a more extensive hourglass shape. The upper central region has bubble-like areas that are the result of the central star’s sporadic ejections. Webb also detected filaments made of molecular hydrogen that have been shocked by past stellar ejections. Learn more about what near-infrared light shows. In mid-infrared light at right, the circumstellar disk, set off in pink and white close to the star, is clearer, while the hourglass shape appears smaller. Webb’s mid-infrared observations showed this region is a mixture of hydrocarbons, ionized neon, and thick dust. See what else mid-infrared light reveals.
NASA, ESA, CSA, STScI

Webb recently studied Herbig-Haro 211, ejections around another small, actively forming star. In the telescope’s near-infrared image, its outflows play the starring role. (The star itself is covered by its circumstellar disk at the center.) The protostar has repeatedly spewed stellar winds and jets, which cause high-speed shock waves that bend when they encounter nearby gas and dust, known as bow shocks. Webb’s highly detailed observations have helped researchers map the star’s outflows and show that the inner jet “wiggles” with mirror symmetry on either side of the central protostar.

The telescope has also surveyed wider areas of star formation, including the iconic Pillars of Creation. The Hubble Space Telescope made these pillars famous decades ago, showing them to be huge columns of gas and dust that have not yet been eroded by nearby hot, massive stars. Webb’s near-infrared observations allow it to peer inside the pillars, revealing additional and complex star formation. Webb’s mid-infrared light view shows even more, including that the stars in the red tips are slowly eroding the dust immediately around them. Want to see this scene in greater detail? Learn how massive young stars just off frame are also eroding the pillars.

Layers of semi-opaque brown- and purple-colored gas and dust that starts at the bottom left and goes toward the top right. There are three prominent pillars rising toward the top right. The top pillar is the largest and widest. The peaks of the second and third pillars are set off in darker shades of brown and have red areas.
This image combines data from Webb’s near- and mid-infrared observations of the Pillars of Creation, including thousands of stars that show up in near-infrared light, and all the dust that pops out in mid-infrared light. Examine the image in detail.
NASA, ESA, CSA, STScI; Image Processing: Joseph DePasquale (STScI), Alyssa Pagan (STScI), Anton Koekemoer (STScI)

Scrutinizing the Environments Around New Stars

As smaller stars finish forming, leftover material known as circumstellar disks orbit them. This is where planets can form over millions of years. Before Webb, researchers theorized that pebbles and rocks delivered molecules and elements as they drifted from the outer to the inner disk around the star. Webb’s observations confirmed this prediction, definitively proving that icy pebbles can drift toward the inner disk, subsequently warming to release cold water vapor into the disk.

Infographic comparing pebble drift in a compact protoplanetary disk to pebble drift an extended protoplanetary disk.
This illustration shows the difference between pebble drift and water content in a circumstellar disk around a star based on data from Webb’s Mid-Infrared Instrument (MIRI). In the compact disk on the left, as the ice-covered pebbles drift inward toward the warmer region closer to the star, their ice turns to vapor and provides a large amount of water. On the right is an extended disk with rings and gaps. As the ice-covered pebbles begin their journey inward, many become stopped by the gaps and trapped in the rings, and fewer icy pebbles are able to deliver water to the inner region of the disk.
Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

Webb has identified water elsewhere, too. The telescope also confirmed water in the inner disk of planetary system PDS 70. Where the telescope located water is critical. At less than 100 million miles (160 million kilometers) from the star, water was found where rocky, terrestrial protoplanets may be gathering mass, which means that if planets do form there, water is immediately available.

Within the Orion Bar, Webb identified a crucial carbon molecule known as methyl cation (pronounced cat-eye-on) for the first time. This complex molecule has been long theorized to aid the formation of additional complex carbon-based molecules. Webb’s detection confirms the importance of methyl cation in the chemical reactions that happen on the surface of cold dust grains. These reactions can build up additional complex molecules, which may also lead to the production of amino acids and the building blocks of life — exciting news that will help researchers update models of star and planet formation.

Webb isn’t doing this work alone. Its observations of circumstellar disks are supported by ongoing, extensive observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. ALMA has delivered detailed information in radio light about the cooler, outer regions of circumstellar disks for over a decade, while Webb specializes in observing warm gas and dust their inner disks. Now that Webb has proven material can migrate from the outer to the inner disk, researchers will establish a more complete picture of actively developing planetary systems.

What’s Next for Webb

Webb’s discoveries about star-forming regions have only begun. Researchers are poring over copious images and datasets in both near- and mid-infrared light to continue advancing what we know. Expect to learn a lot more about fitful, actively forming stars along with the elements and molecules that surround them. We will continue to see high-resolution portraits of star forming regions throughout our Milky Way galaxy and also learn about star formation in nearby galaxies, including those already observed. Webb will also gather information about star formation where there are fewer elements other than hydrogen and helium, helping researchers better theorize how stars formed in the early universe. Soon, researchers using Webb will improve models of star formation, and more accurately trace the star formation process from start to finish.

Keep Up to Date with Webb Science

Keep an eye on the news and follow Webb on Facebook, X, and Instagram.