NASA’s Webb unveils young stars in early stages of formation

The Cosmic Cliffs, a region at the edge of a gigantic, gaseous cavity within the star cluster NGC 3324, has long intrigued astronomers as a hotbed for star formation. While well-studied by the Hubble Space Telescope, many details of star formation in NGC 3324 remain hidden at visible-light wavelengths. Webb is perfectly primed to tease out these long-sought-after details since it is built to detect jets and outflows seen only in the infrared at high resolution. Webb’s capabilities also allow researchers to track the movement of other features previously captured by Hubble.

Recently, by analysing data from a specific wavelength of infrared light (4.7 microns), astronomers discovered two dozen previously unknown outflows from extremely young stars revealed by molecular hydrogen. Webb’s observations uncovered a gallery of objects ranging from small fountains to burbling behemoths that extend light-years from the forming stars. Many of these protostars are poised to become low mass stars, like our Sun.

Dr Kuhn’s work on the project involved identifying and characterising the young stars that produce the outflows. “Some of these stars are too bright in the infrared for JWST, so they saturate its detectors”, Dr Kuhn explained. “I therefore used data from the Spitzer Space Telescope to classify young stars in the region. One important diagnostic is how the stars' emitted energy is distributed in the infrared, since stars at earlier stages of formation tend to have more energy at longer infrared wavelengths. We found that the outflows seen in the JWST images preferentially come from stars in the earliest stages of evolution”.

Molecular hydrogen is a vital ingredient for making new stars and an excellent tracer of the early stages of their formation. As young stars gather material from the gas and dust that surround them, most also eject a fraction of that material back out again from their polar regions in jets and outflows. These jets then act like a snowplow, bulldozing into the surrounding environment. Visible in Webb’s observations is the molecular hydrogen getting swept up and excited by these jets.

“Jets like these are signposts for the most exciting part of the star formation process. We only see them during a brief window of time when the protostar is actively accreting,” explained co-author Nathan Smith of the University of Arizona in Tucson.

Previous observations of jets and outflows looked mostly at nearby regions and more evolved objects that are already detectable in the visual wavelengths seen by Hubble. The unparalleled sensitivity of Webb allows observations of more distant regions, while its infrared optimisation probes into the dust-sampling younger stages. Together this provides astronomers with an unprecedented view into environments that resemble the birthplace of our solar system.

This period of very early star formation is especially difficult to capture because, for each individual star, it’s a relatively fleeting event – just a few thousand to 100,000 years amid a multi-million-year process of star formation.

Dr Kuhn commented: "The Early Release Observation program is an amazing showcase of Webb's capabilities. It’s exciting to see star formation at this level of detail in a distant, extreme environment like the Cosmic Cliffs."

In analysing the new Webb observations, astronomers are also gaining insights into how active these star-forming regions are, even in a relatively short time span. By comparing the position of previously known outflows in this region caught by Webb, to archival data by Hubble from 16 years ago, the scientists were able to track the speed and direction in which the jets are moving.

This science was conducted on observations collected as part of Webb’s Early Release Observations Program. The paper was published in the Monthly Notices of the Royal Astronomical Society in December 2022.

Image credit: NASA, ESA, CSA, and STScI. Image processing: J. DePasquale (STScI).