Unusual 'ingredients' helped stars form in a galaxy near the Milky Way

Some newly found stars in a small galaxy called Sextans A are forming without some of the usual "ingredients" — raising questions about how the early universe evolved.

The astronomers behind a new study of these stars likened the stars' environment to a cosmic kitchen. Usually, stars being "cooked" in these kitchens are made up of essential ingredients like silicon, carbon and iron. Sextans A, however, is missing almost all of those ingredients, creating a situation where something as essential as metaphorical sugar, or flour, is absent from the "kitchen" where the stars form, researchers stated.

"Every discovery in Sextans A reminds us that the early universe was more inventive than we imagined," lead author Martha Boyer, an associate astronomer at the Space Telescope Science Institute in Baltimore, said in a NASA statement. (The institute operates JWST, and coordinates its observations.)

Boyer was part of the team studying these stars, and the environment between them, with the James Webb Space Telescope. Scientists published the work in two studies highlighted in a press conference this week at the American Astronomical Association's annual meeting in Phoenix. One study was published in September 2025 in the peer-reviewed Astrophysical Journal Letters (ApJ), while the other study is awaiting peer review after being published on preprint server arXiv in December.

The ApJ study examined the spectra, or light signatures, of half a dozen stars in Sextans A, which is near our home Milky Way galaxy. Sextans A has a very low metal content, or metallicity, compared to the sun — just 3% to 7%. That's because the galaxy is not massive enough to hold on to heavier elements, like iron and oxygen, produced by old stars and supernovas (the explosions of massive, old stars that run out of fuel to burn).

Using JWST's Mid-Infrared Instrument, the scientists honed in on stars, all between one and eight times the mass of the sun, that are late in their lifetimes. These are called asymptomatic giant branch (ASB) stars at the red giant phase of existence, before they explode and collapse into white dwarfs.

Usually, ASB stars produce silicate dust in metal-rich galaxies, said Boyer, who led the ApJ study. "However, at such low metallicity [in the galaxy], we expect these stars to be nearly dust-free," she added. "Instead, Webb revealed a star forging dust grains made almost entirely of iron. This is something we've never seen in stars that are analogs of stars in the early universe."

Astronomers wouldn't expect stars missing those key 'ingredients' to be able to create much dust at all. The JWST revealed that not only are the stars producing dust, but one of them was able to do so using an entirely different chemical "recipe."

The second study in arXiv looked at the interstellar medium (the environment between stars) in Sextans A, searching for carbon-bearing molecules called polycyclic aromatic hydrocarbons (PAHs). Models suggest that PAHs would best form in metal-rich galaxies, unlike Sextans A. Yet scientists still found "pockets" of PAHs in the dwarf galaxy.

"Webb shows that PAHs can form and survive even in the most metal-starved galaxies, but only in small, protected islands of dense gas," Arxiv study lead author Elizabeth Tarantino, a postdoctoral researcher at the Space Telescope Science Institute, said in the same statement.

The study authors suggest the PAHs came together where the density of gas, and shielding of dust, gave just enough protection. By association, this would mean that PAHs tend to be difficult to find in metal-poor galaxies because these galaxies often lack such protection.

Astronomers plan to peer at Sextans A again with JWST to search out more PAHs, using high-resolution spectroscopy. The planned observations may give more information about the PAH clump chemistry. But in the meantime, team members stated, the two studies show potential other ways of creating dust than supernovas, and that cosmic environments with low metallicity have more dust than models predicted.