The NGC 7027 nebula, nicknamed the “jewelry nebula”, captured by the Hubble space telescope. This dying star expels ionized gas jets forming a recently observed clover motif, testifying to a much more dynamic activity than expected. A cosmic environment rich in molecular hydrogen, closely linked to the chemistry of the origins of the universe. © NASA, ESA, et J. Kastner (Rochester Institute of Technology)
Long considered the very first molecule formed in the universe, the Helium Hydride (HEH⁺) has just been recreated in extreme conditions by German researchers. Their goal: to test how this molecule reacts at very low temperature. Their discovery? In reverse of theoretical predictions, this reaction does not slow down. A fascinating anomaly… and fraught with consequences for cosmology.
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Big Bang: a discovery calls into question 40 years of cosmic models
Previous theories predicted a sharp drop in probability of a low -temperature reaction, but neither the experience nor the new calculations made it possible to confirm this.
At Max-Planck-Institut Für Kernphysik, in Heidelberg, Dr Holger Kreckel’s team managed to simulate the reaction of the Heh⁺ ion with Deuterium in an environment close to the interstellar vacuum, only a few kelvins. The experiment, carried out in the CSR cryogenic ring 35 meters in diameter, made it possible to maintain the ions for 60 seconds while precisely controlling the energy of the collisions.
“Previous theories predicted a sharp drop in probability of low -temperature reaction, but neither the experience nor the new calculations made it possible to confirm this,” Explain Dr Kreckel. In other words, the more temperature we went down, the more physicists thought that the molecule would become lazy, almost unable to react.
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Diagram of the reaction studied between the Helium Hydride (HEH⁺) and a deuterium atom, recreated in the laboratory. Unlike old theories, the reaction is done without energy bar and remains effective even at very low temperature. In the background: the planetary nebula NGC 7027, rich in molecular hydrogen (in red). © Schéma : MPIK Heidelberg. Image de fond : W. B. Latter (SIRTF Science Center/Caltech) et NASA.
However, surprise: even in a cold close to absolute zero, the Heh⁺ ion continues to react with the Deuterium at a stable rate. As if the cold had little effect on his chemistry. This unusual behavior forced researchers to review the old models, and to correct an error in the theoretical calculations used for decades.
This unexpected result supports the new calculations carried out by the group of the theorist physicist Yohann Scribano, who has corrected an error in the potential surface used so far. “The reactions between HEH⁺ and hydrogen or deuterium therefore played a much more important role than expected in the chemistry of the primordial universe,” concludes Kreckel.
The reactions between Heh⁺ and hydrogen or deuterium therefore played a much more important role than expected in the chemistry of the primordial universe.
The involvement is direct: if Heh⁺ reacts as well even in the extreme cold, it means that it could help the first clouds of gas to cool much faster than we thought. However, this cooling is essential for these clouds to collapse under their own weight and give birth to the first stars. Thanks to its ability to “evacuate” energy in the form of light (by vibrating and turning like a tiny antenna), this small ion could therefore have played a key role in the appearance of the very first light sources of the universe.
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