The first molecule of the universe detected in space

Scientists have detected for the first time the oldest molecule type of our universe in space.

Helium hydride ion (HeH +) was the first molecule to form when, nearly 14 billion years ago, temperatures dropped in the young universe allowed the recombination of light elements produced in the Big Bang.

At that time, the atoms of ionized hydrogen and neutral helium reacted to form HeH +, said researchers at the Max Planck Institute for Radioastronomy (MPIfR) in Germany.

Despite its importance in the history of the primitive universe, HeH + has so far escaped any detection in astrophysical nebulae – cloud of gas and dust in outer space.

Exploiting the BIG far infrared spectrometer aboard the SOFIA flying observatory, an international team reported unambiguous detection of the molecule in the planetary nebula NGC 7027.

At the beginning of the chemistry, when the temperature in the young universe had fallen below 4000 Kelvin, the ions of the light elements (hydrogen, helium, deuterium and lithium traces) produced in the nucleosynthesis of the Big Bang recombined in the reverse order of their ionization potential.

Helium first combined with free electrons to form the very first neutral atom, according to the study published in the journal Nature.

At that time, hydrogen was still ionized or present as bare protons.

Helium atoms combined with these protons form the helium hydride ion HeH +, the first molecular bond in the universe.

As recombination progressed, HeH + reacted with then neutral hydrogen and created a first path to molecular hydrogen formation – marking the beginning of the modern universe.

Despite its undisputed importance in the history of the primitive universe, the HeH + molecule has so far eluded detection in interstellar space, researchers said.

Studied in the laboratory since 1925, the specialized research carried out during the last decades was unsuccessful, thus putting into question our understanding of the underlying chemical networks, they declared.

"The chemistry of the universe began with HeH +. The absence of definitive proof of its very existence in interstellar space has been a dilemma for astronomy for a long time, "said Rolf Gusten of MPIfR.

By the late 1970s, astro-chemical models suggested the possibility that HeH + would exist at detectable abundances in local astrophysical nebulae and be more easily observed in so-called planetary nebulae, ejected by Sun-like stars at the last stage of their life. .

The hard radiation field produced by the central white dwarf star with a temperature of more than 100 000 degrees causes the ionization fronts in the ejected envelope, where it 's possible. expect HeH + to be formed.

The molecule will emit its most powerful spectral line at a characteristic wavelength of 0.149 mm.

However, the atmosphere of the Earth is opaque at this wavelength for terrestrial observatories, which makes it necessary to carry out this research in space or in a high-altitude observatory such as SOFIA navigating above the absorbing layers of the lower atmosphere.

"With the recent advancements in terahertz technologies, it is now possible to perform high resolution spectroscopy at the required wavelength in the far infrared," Gusten said.

Using the BIG spectrometer onboard SOFIA, the team is now reporting the unequivocal detection of HeH + on the envelope of the NGC 7027 planetary nebula.

"The discovery of HeH + is a spectacular and magnificent demonstration of nature's tendency to form molecules," said David Neufeld of Johns Hopkins University in the United States.

"Despite the unpromising ingredients that are available, a mixture of hydrogen and helium, a nonreactive rare gas, and a hostile environment, at thousands of degrees Celsius, form a fragile molecule," Neufeld said.

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"Notably, this phenomenon can not only be observed by astronomers but also understood with the help of the theoretical models we have developed," he said.

The detection of this special molecule brings a long search to a happy ending and eliminates the doubts that we could not understand the underlying formation and destruction as well as we thought, researchers said.