Baby 'failed star' has unusually rich planet-forming disk, James Webb Space Telescope finds

Astronomers using NASA's James Webb Space Telescope (JWST) have spotted the most chemically rich disk ever observed around a brown dwarf, a cool, faint object sometimes dubbed a "failed star."

The finding comes from Cha Hα 1, a young brown dwarf encircled by a swirling disk of gas and dust where planets may one day take shape.

Though they never sustain hydrogen fusion like true stars, brown dwarfs and their disks offer vital clues about how planetary systems form. Webb's detection of this unprecedented chemical brew suggests that even these stellar underdogs could host the raw ingredients for planet birth.

This is because low-mass stars and brown dwarfs don't produce as much radiation or heat as stars like our sun. Their surrounding disks of gas and dust are therefore cooler, thinner and have weaker pressure and turbulence. These conditions change how dust grains and molecules behave: icy, water-rich particles can drift inward more rapidly and get swallowed by the star, while lighter carbon-rich material is more likely to remain behind.

The calmer environment also slows down mixing in the disk, meaning that chemical differences between regions can persist longer than they would around hotter, more energetic stars.

"In the disks [around low-mass stars and brown dwarfs], water-rich dust grains move quickly and are accreted by the star, leaving behind the more carbon-rich dust," Kamber Schwarz, a postdoctoral researcher at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, told Space.com.

"Planets that form in these disks are likely to have a much different chemical composition than planets that form around more sun-like stars," added Schwarz, a co-author of a study about the new results that's available on the preprint site arXiv.

"The results provide a rare, detailed look at how planet-forming chemistry operates in the extreme environments around brown dwarfs, potentially offering clues to the diversity of worlds beyond our solar system," added Thomas Henning, a professor at MPIA.

The researchers observed Cha Hα 1 with JWST's Mid-Infrared Instrument (MIRI) in August 2022, and the results line up closely with data collected nearly two decades earlier by NASA's now-retired Spitzer Space Telescope.

That agreement is important, because it confirms that the rich chemistry seen with Webb isn't just a fleeting feature or an observational artifact but rather a persistent characteristic of the brown dwarf's disk. Spitzer hinted at this complexity back in 2005, but Webb's sharper vision now reveals the full inventory of molecules with far greater clarity.

Cha Hα 1 is encircled by a disk rich in hydrocarbons like methane, acetylene, ethane and benzene, along with water, hydrogen, carbon dioxide (CO2) and large silicate dust grains.

"It is interesting that we see both hydrocarbons and oxygen-bearing molecules in the JWST data," said Schwarz. "Carbon loves bonding with oxygen, [and the fact that] we don't see any oxygen in these hydrocarbons tells us that they formed in a very oxygen-poor region of the disk, different from the region the water and CO2 is coming from."

Typically, older disks lean one way or the other: oxygen-rich environments produce abundant water and silicates, while carbon-rich environments favor carbon- and hydrogen-based molecules called hydrocarbons. Seeing both at once suggests that the chemistry of Cha Hα 1's disk is complex, perhaps shaped by temperature differences across the disk, turbulence that mixes material or simply its age.

"We think, [as a result], this disk is younger than disks around other brown dwarfs," said Schwartz.

The MIRI data also revealed emission from large silicate dust grains in the upper layers of the inner disk, showing that dust grains are already starting to grow even at this very young stage.

"Dust creates a solid surface in space, which is essential to form complex molecules," said Henning. "Large dust grains don't exist in the interstellar medium but are important for planet formation. Having dust grains in a range of sizes … allows giant planet cores to grow much more quickly than if all the dust was the same size."

The fact that simpler molecules like carbon dioxide and hydroxide (-OH) are largely absent, while larger, more complex molecules are present, suggests that the disk is already at an advanced stage of chemical evolution.

"[Comparing] disks at different points in their evolution lets us test our theories about what is driving this evolution and ultimately gives us a better understanding of the material available to forming planets at different times," said Schwartz.

The team say there are some spectral features in Cha Hα 1's disk that don't match any molecules studied in Earth-based labs, suggesting the presence of previously unobserved or poorly understood molecules that need resolving.

"We've also only been able to characterize the gas properties and dust properties separately," said Henning. The team have identified what is in the disk, but not yet how the dust and gas work together to shape its evolution. To do that, "we need to look more at how the dust and gas interact with each other," Henning added.

The disk's unusually rich mix of molecules offers a rare chance to study how chemistry shapes planet formation. Understanding these molecular reservoirs could reveal what kinds of planets might eventually emerge around brown dwarfs.