First Time in 40 Years: James Webb Telescope Detects Forbidden Radiation from Trihydrogen Cation

The James Webb Space Telescope detected a rare type of light emitted by the trihydrogen cation, known as H3+, in a discovery never previously recorded in space or laboratories.

This observation provides scientists with a new tool to study cosmic chemistry and hot gases surrounding stars in the formation phase.

The discovery comes after nearly four decades of theoretical predictions regarding this type of emission, known as the pure rotational spectrum of the trihydrogen cation.

Researcher David Neufeld from Johns Hopkins University led the study, and its results have been accepted for publication in the journal "Astrophysical Journal Letters."

The signal originated from hot gas within the "Herbig-Haro 168" object, located in a star-forming region approximately 2,300 light-years from Earth.

Detecting the Rare Signal

The trihydrogen cation consists of three hydrogen nuclei sharing two electrons, taking the shape of an equilateral triangle, which gives it distinct electrical properties.

This ion lacks a permanent electric dipole moment, so it does not typically emit electromagnetic radiation during rotation.

However, astrophysicists Fu Shi Ban and Takeshi Oka predicted in 1986 that the ion might emit faint light due to slight distortion occurring during its rotation.

Centrifugal force causes a limited change in the ion's geometric symmetry, generating a small electric moment that allows for light emissions known as "forbidden transitions."

Describing them as forbidden does not mean they violate the laws of physics, but rather that they are weak transitions that do not occur according to standard spectral rules.

This signal remained undetected for about 40 years due to its extreme weakness, until the James Webb Telescope was able to discover it using the Mid-Infrared Instrument (MIRI).

Secrets of Cosmic Molecules

Herbig-Haro objects arise when jets ejected by newborn stars collide with the surrounding gases and dust.

This collision generates shock waves that heat the gas to thousands of degrees, causing it to glow and emit detectable radiation.

The James Webb Telescope managed to penetrate the cosmic dust surrounding star-forming regions thanks to its ability to observe infrared rays.

Researchers identified 26 spectral lines emitted by the trihydrogen cation, each exceeding five "sigma" strength in at least one of the two observation regions.

The strongest spectral line registered a significance of 72 sigma, a statistical measure indicating that the probability of the signal being caused by random noise is extremely low, and not a unit for measuring electric charges.

The results showed that emissions from the trihydrogen cation follow the distribution of hot molecular hydrogen within the gas affected by shock waves.

However, current models failed to fully explain the intensity of the signal, as some models underestimated the observed emissions by between five and six times.

These spectral lines may help in the future to study ionization rates within hot gases surrounding emerging stars and understand chemical reactions occurring in space.