The signal hunted for 40 years: astronomers detect H₃⁺ ion radiation in space for the first time

Astronomers have for the first time detected in space the radiation of a molecule consisting of three hydrogen atoms and carrying an electric charge — the H₃⁺ ion. This is reported by RBC-Ukraine with reference to a study published on the arXiv preprint server. Physicists predicted the existence of such a signal back in 1986, but it has taken scientists almost four decades to confirm it with observations.

How a molecule that «should not» glow radiates anyway

The mechanism was explained in 1986 by astrophysicists Fu-Shi Pan and Takeshi Oka from the University of Chicago. At rest, the H₃⁺ ion has a symmetric shape close to an ideal triangle and is incapable of emitting light. But when rotating, its shape slightly distorts: a minor asymmetry arises, which causes a weak electric field to appear. It is this field that allows the molecule to radiate. The problem was that the signal turned out to be extremely weak — for almost 40 years it could not be detected even under laboratory conditions.

Why the discovery became possible only now

The breakthrough came with the James Webb Space Telescope (JWST), which is capable of recording extremely weak infrared radiation. Astronomers pointed it at young stars ejecting powerful gas flows into space at speeds of hundreds of kilometers per second. When these flows collide with surrounding gas clouds, shock waves and bright regions known as Herbig-Haro objects arise. By analyzing the telescope's infrared data on object HH 168 in the Cepheus A star-forming region, the researchers noticed a series of very weak signals whose characteristics matched the H₃⁺ ion radiation predicted by Pan and Oka in 1986.

26 signals and 72-sigma statistical significance

In total, the scientists found 26 such signals. The strongest one exceeded a statistical threshold of 72 sigma, which means the probability of a random coincidence is practically zero. Later, astronomers found the same radiation in archival data of another similar object — HH 211, which further confirms the result.

What this means for astronomy

According to the researchers, the discovery provides a new tool for studying gas flow collisions in space and the processes occurring around young stars. The H₃⁺ ion, which remained «invisible» for decades, can now become a marker for analyzing shock waves and chemistry in star-forming regions.