Oldest type of molecule in the universe detected in space | Science

The oldest type of molecule in our universe has been detected in space, scientists have revealed, supporting theories of how the early chemistry of the universe developed after the Big Bang.

It is believed that the positively charged molecule known as helium hydride has played a prominent role in the early universe, forming when a helium atom shared its electrons with a hydrogen or proton nucleus. Not only is it thought to be the first molecular bond, and the first chemical compound, which appeared when the universe cooled after the Big Bang, but also opened the way for the formation of hydrogen molecules.

But while helium hydride was produced in the laboratory almost a century ago, it has proved difficult to detect in space, despite predictions that it should be present in the gas clouds in which the stars are born, as well as in the gas expelled by the stars when they die. .

"Although [helium hydride] It is of limited importance on Earth today, the chemistry of the universe began with this ion, "the authors write." The lack of definitive evidence of its existence in interstellar space has been a dilemma for astronomy. "

Now experts say they have finally discovered helium hydride in a small but bright planetary nebula 600 years old, about 3,000 light-years away, in the constellation Cygnus. While this helium hydride was formed by a process different from that of the early universe, the team says that its presence supports theories of what was happening in the "dawn of chemistry," which led to "a decades-long search for a happy ending in last ".

Dr. Jérôme Loreau, an expert in helium hydride at the Université Libre de Bruxelles, who was not involved in the study, said the findings were exciting, and noted that although large organic molecules had been found in space, helium hydride , much simpler, had proved difficult. to track down.

"Another reason why it's exciting is that HeH + [helium hydride] It is the first molecule that formed in the universe, approximately 380,000 years after the Big Bang, in an era known as the time of recombination, "said Loreau, adding that the molecules that appeared in this period, as the universe cooled, then led to the formation of stars and galaxies. "Therefore, it is very exciting to have finally observed one of the building blocks of the molecular universe."

One difficulty in detecting helium hydride is that the telltale signs based on the light it emits after the electrons hit them tend to be obscured by the almost superimposed "signatures" of a different molecule composed of carbon and hydrogen, without However, new instruments have been triumphant. .

Writing in the journal Nature, the team report they made their discovery by examining a planetary nebula known as NGC 7027 in which layers of gas are lost from its hot core, a white dwarf.

The data was collected using an instrument aboard a mission known as Sofia, a joint project between NASA and the German Aerospace Center, in which a specially modified Boeing 747SP aircraft flies very high in Earth's atmosphere, up to approximately 13,700 meters (45,000 feet). ), carrying a 2.7 meter telescope and other instruments. At this point, the instruments are above the vast majority of water vapor on Earth, which would otherwise hide the signals of other molecules.

Fundamentally, these instruments offer a very high resolution, allowing the light of the helium hydride to be distinguished from the signatures of other molecules at very similar wavelengths.

Professor Phillip Stancil, a helium hydride expert at the University of Georgia, also said the discovery was exciting, but noted that only one "signature" of helium hydride was detected, and two are generally necessary to be sure.

But Dr. Rolf Güsten, of the Max Planck Institute for Radio Astronomy in Bonn, Germany, and first author of the research, said the possibility that the identification is incorrect is negligible, adding that the findings solve a long-standing enigma.

"The lack of evidence of the very existence of helium hydride in the local universe has challenged our understanding of chemistry in the early universe," he said. "The detection reported here resolves such doubts."

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