In the atmosphere of brown dwarfs, cyanogen and acetylene were discovered for the first time.

Brown dwarfs are often referred to as "failed stars": their mass ranges from 13 to 80 times that of Jupiter, which is insufficient to initiate stable hydrogen fusion, a process characteristic of other celestial bodies. These objects form from gas clouds (similar to stars) and cool down over time. Scientists categorize brown dwarfs into four main spectral classes: M (up to M7), L, T, and Y (listed in order of decreasing temperature).

Specifically, the maximum temperature of L-class brown dwarfs does not exceed 2227°C, while the coldest among them (Y class) can reach 27°C. Under such conditions, complex compounds can form in the atmospheres of these celestial bodies, such as water (H₂O), methane (CH₄), and ammonia (NH₃), which leave distinctive signatures in infrared spectra.

Now, after examining the atmospheres of the stars in the WISE‑0458 system (or WISE J045853.90+643451.9) in the mid-infrared range using the MIRI spectrograph aboard the Webb telescope, the authors of a new scientific paper, published on the Cornell University preprint server, identified hydrogen cyanide (HCN) and acetylene (C₂H₂) in them.

It is noteworthy that both celestial bodies in the studied star system belong to one of the "coldest" categories: their temperatures are approximately 327°C and 227°C, respectively. Previously, it was believed that the atmospheres of T-class brown dwarfs were nearly identical.

A research team led by Elisabeth C. Matthews from the Max Planck Institute for Astronomy (Germany) analyzed the spectral data and expectedly found the presence of water, methane, and ammonia molecules, which create characteristic absorption lines.

The discovery of the two rare compounds, hydrogen cyanide and acetylene, was a surprise: the high concentration of HCN indicated strong vertical mixing of molecules in the atmosphere of WISE-0458, leading astronomers to conclude that hot gases from the deep layers of the stars' atmospheres were rapidly rising and "freezing" chemical reactions, preserving hydrogen cyanide at altitudes where it can be observed.

However, explaining the high concentrations of acetylene in the atmospheres of brown dwarfs proved challenging, as standard models did not predict this. On Jupiter, for example, C₂H₂ forms under the influence of sunlight, which breaks down methane, but WISE-0458 does not receive such radiation. Moreover, even maximum mixing or increased metallicity of the atmosphere does not account for its presence in such quantities.

Astronomers have proposed several hypotheses to explain the high concentrations of C₂H₂, including magnetic activity that generates auroras or lightning strikes that ionize gases and trigger unusual chemical processes.

"This discovery opens a new era in studying the chemistry of such substellar objects and allows for a detailed examination of the mechanisms of formation and evolution of molecular compositions not only of brown dwarfs but also of exoplanets with similar atmospheric conditions," explained the authors of the new study.

The results also demonstrated the exceptional capabilities of the Webb telescope for studying cold atmospheres, where even small quantities of molecules can be detected with high precision. Further research and observations using other astronomical instruments will help unravel the mysterious chemical processes identified in the WISE-0458 system and refine the data.