Webb Released One of Its Largest Images Yet, a Star Nursery 1,000 Light-Years Away in Perseus. Hiding in It Are Brown Dwarfs Just Twice the Mass of Jupiter, Smaller Than Theory Says Should Be Possible.

NASA released one of the largest images yet produced by the James Webb Space Telescope on Tuesday: a sweeping near-infrared view of IC 348, a star-forming region roughly 1,000 light-years from Earth in the constellation Perseus. The picture is full of the usual drama of a stellar nursery, with newborn stars blasting jets into the gas and dust around them. But the objects the astronomers were hunting are the ones you can barely see.

The team, led by Kevin Luhman of Penn State with Catarina Alves de Oliveira of the European Space Agency, used Webb to answer a deceptively simple question: how small can the smallest object made by star formation be? Stars form when cold clouds of molecular hydrogen collapse under their own gravity. Anything that ends up below about 8% of the Sun's mass never gets hot enough in its core to fuse ordinary hydrogen and becomes a brown dwarf, an object that forms like a star but never ignites like one. The lower limit of that process is where the models get shaky.

In 2022 the same group used Webb to find brown dwarfs in IC 348 with masses of just three to four Jupiters. For the new work they went deeper. NIRCam, Webb's near-infrared camera, imaged the region in 2024 to pick out the warm glow of young brown dwarfs and protostars, and candidates were selected by color and brightness. In 2025 the team followed up with NIRSpec, the spectrograph, to measure the objects' masses directly. The results, published last year in The Astrophysical Journal Letters, turned up brown dwarfs with masses as low as twice that of Jupiter, about 0.19% of the Sun's mass. That is smaller than the collapse of a gas cloud is supposed to be able to produce, and it makes these the least massive brown dwarfs known.

Two other findings came out of the spectra. One of the lightest new brown dwarfs shows signs of a surrounding disk, which raises the possibility of small planets forming around an object that is itself only planet-sized. And the spectra of the lowest-mass objects carry an absorption feature the team attributes to an unidentified hydrocarbon, a molecule built only of hydrogen and carbon. That signature has only ever been seen in the coolest, lightest brown dwarfs, which suggests they may deserve a spectral class of their own.

The rest of the image rewards a closer look. The upper right corner holds a dense cluster of protostars, several accompanied by Herbig-Haro objects, the glowing shock fronts that appear where a young star's jet slams into surrounding gas. The long horizontal streak there is HH 797, which on inspection turns out to be two protostars driving nearly parallel outflows. Just to its right is HH 211, shaped like a propeller, with both narrow jets and broad outflows. NASA's collage of insets from the image adds embedded stars, the central cluster, faint outflows, a gravitationally lensed background source and a handful of distant spiral galaxies that happened to be in the field.

The data come from Webb General Observer Program 4866, which will go on to compare how the population of planetary-mass objects differs from one star-forming region to the next and to chase down the origin of that hydrocarbon feature. The immediate lesson is that the boundary between what counts as a star and what counts as a planet is blurrier, and lower, than the textbooks have it. Something twice the mass of Jupiter, formed from a collapsing cloud rather than in a disk around a star, is now a thing that exists.