Astronomers have spotted the first molecule of the universe | Science

The very first molecule in the universe, which would have been created after the big bang, was detected in space for the first time. Helium hydride (HeH), a combination of helium and hydrogen, has been spotted some 3,000 light-years from Earth by an instrument on board the aircraft. Airborne observatory of the stratosphere for infrared astronomy (SOFIA). parts of the Earth's atmosphere.

It has long been thought that HeH marked "the dawn of chemistry," while the remains of the big bang cooled to about 4000 K and the ions began to associate with electrons to form neutral atoms. . The researchers believe that in this primordial gas, neutral helium reacted with hydrogen ions to form the first chemical bond connecting the very first molecule.

In 1925, chemists synthesized HeH in the laboratory. In the 1970s, theorists predicted that the molecule could exist today, probably formed again in planetary nebulae, clouds of gas ejected by stars similar to the dying sun. But decades of observations have not allowed to find any, which casts doubt on the theory.

To find the elusive molecule, astrochimists search for the characteristic frequencies of the light it emits, in particular a far-infrared spectral line typically blocked by the Earth's atmosphere. But a far infrared spectrometer embedded on SOFIA allowed them to find this signature for the first time in a planetary nebula called NGC 7027 (photo above), report today the researchers in Nature. The result shows that this unlikely molecule – involving generally unreactive helium – can be created in space. Once this cornerstone is confirmed, it seems that the evolution of the next 13 billion years of chemistry rests on a firmer ground.