A team led by David Neufeld of Johns Hopkins University has detected a 'forbidden' spectral signal from the trihydrogen cation (H3+), a molecule of three hydrogen nuclei sharing two electrons that is often called 'the molecule that made the Universe.'

The signal was found in Herbig-Haro 168, a region of gas and dust in the Cepheus A star-forming region, and in archive data from a second object, Herbig-Haro 211. The study has been accepted for publication in The Astrophysical Journal Letters.

H3+ helps drive the chemistry that builds complex molecules in cold interstellar clouds and acts as a coolant that lets those clouds collapse under gravity to form stars.

The molecule's shape is the key: trihydrogen forms a perfect equilateral triangle, so its electrical charge is evenly distributed, meaning quantum rules dictate it cannot emit conventional radiation as it rotates.

In 1986, Fu-Shih Pan and Takeshi Oka of the University of Chicago calculated a loophole — centrifugal forces distort the molecule's symmetry just enough to create a tiny electric imbalance, allowing extraordinarily faint emission.

Clarín reports that this light is so weak it went undetected for 40 years both in space and in terrestrial laboratories, but in the near vacuum of interstellar space even forbidden transitions can build up enough light to be seen with a telescope sensitive enough — and Webb, the largest telescope ever flown, proved sensitive enough.

The evidence is overwhelming: the team identified 26 distinct spectral lines from trihydrogen, with wavelengths that perfectly matched the forbidden rotational transitions calculated by Pan and Oka.

The strongest line registered a massive 72 sigma — a level of statistical certainty far beyond what scientists normally require to claim a definitive detection. The finding was not an isolated event either.

When the team reviewed archival Webb observations of Herbig-Haro 211, they found the same telltale trihydrogen emission, confirming the result in a second object.

According to Clarín, the newly detected H3+ signals closely tracked emissions of ordinary molecular hydrogen, suggesting both molecules respond to the same violent shock conditions.

Herbig-Haro objects form when newborn stars fire jets of gas at hundreds of kilometers per second into surrounding clouds, generating shock waves that heat the gas to thousands of degrees. The new lines come from these heated regions and can reveal details that other signals cannot.

Clarín reports that current computer shock models cannot yet fully explain why the trihydrogen emission burned so brightly — an open puzzle.

By reading these forbidden signals, astronomers can now measure temperature, density and energy flow inside the dusty stellar nurseries where stars are born and the chemical foundations of the cosmos are built.