Brown dwarfs in Webb's stellar nursery

At first glance, it is pure wonder. Then the eye adjusts, slows down, begins to follow the filaments, to distinguish the jets, to search among the stars for what was previously missed. This image of Ic 348, obtained from the James Webb Space Telescope, shows a star-forming region about a thousand light-years away from us, in the constellation of Perseus. Here cold clouds of molecular gas collapse under the action of gravity, giving rise to new stars. In the upper right, among the clouds, several protostars appear, some of which expel powerful jets of matter into space. When these jets collide with the surrounding gas and dust, they produce luminous regions called Herbig-Haro objects. The long, almost horizontal structure is Hh 797 and looking more closely, it is discovered that it actually hides two protostars, each with its own jet of matter oriented almost in the same direction as the other. A little further to the right, Hh 211 appears, with its characteristic spiral shape, accompanied by thin jets of matter and broader outflows. Some of these details, along with others more difficult to grasp in the overall view, are collected in a collage that NASA created from the Webb image. But the most interesting surprises of Ic 348 are hidden in the less obvious details. Among the young stars in the region Webb has searched for brown dwarfs, objects that form similarly to stars from the collapse of a molecular cloud, but which do not reach enough mass to sustain hydrogen fusion in their core. The smaller stars have masses around eight percent of the Sun's mass; below this threshold begins the territory of brown dwarfs. One of the goals of the observations of Ic 348 is to understand how small brown dwarfs can be. Kevin Luhman of the Pennsylvania State University and his group had already observed this region with Webb in 2022, identifying brown dwarfs with masses equal to about three or four times that of Jupiter. The new observations went even deeper and, in 2024, the Webb Near-Infrared Camera recorded the weak infrared emission of young brown dwarfs and newborn stars. After selecting the candidates based on color and luminosity, in 2025 the research group studied them with NirSpec, the spectrograph operating in the near-infrared. And this is where the surprise arrived: some of the brown dwarfs identified have a mass equal to just twice that of Jupiter, about 0.19 percent of the Sun's mass. These are the least massive brown dwarfs known so far. Such light objects are not easy to explain with current stellar formation models. The collapse of a cloud should indeed face difficulties in producing bodies of such reduced mass, so their existence suggests that the process leading to the birth of stars and brown dwarfs may push towards even smaller masses than predicted. There is another curious detail: one of the lightest brown dwarfs shows signs of the presence of a disk of material around it. From disks like this, planets can be born, but here the central body already has a mass similar to that of a giant planet. In the spectra of the brown dwarfs, the group has also identified a feature attributed to a hydrocarbon not yet identified, a molecule composed only of hydrogen and carbon: this particular signal has so far been observed only in the atmospheres of the least massive brown dwarfs and could indicate that these extreme objects might belong to a spectral class all their own. Within a single frame coexist collapsing clouds, protostars emitting jets of matter, young stars, tiny brown dwarfs, and distant galaxies in the background. Is it just a photo? Don't tell me about those from Webb.