Chemistry at the Beginning: How Molecular Reactions Influenced the Formation of the First Stars
28.07.2025

Researchers have discovered new insights into the reaction pathways of the first molecule in space.

• The HeH⁺ ion was the first molecule to form in the early universe, before the first stars were born.
• Researchers have investigated reactions of HeH⁺ with hydrogen atoms under conditions similar to those in the early universe for the first time, revealing significant discrepancies with previous theories.
• The results significantly impact our understanding of the early chemistry of the universe and the processes that contributed to the formation of the first stars.

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They found that, contrary to earlier predictions, the rate at which this reaction proceeds does not slow down with decreasing temperature, but remains almost constant. “Previous theories predicted a significant decrease in the reaction probability at low temperatures, but we were unable to verify this in either the experiment or new theoretical calculations by our colleagues,” explains Dr Holger Kreckel from the MPIK. ‘The reactions of HeH⁺ with neutral hydrogen and deuterium therefore appear to have been far more important for chemistry in the early universe than previously assumed,’ he continues. This observation is consistent with the findings of a group of theoretical physicists led by Yohann Scribano, who identified an error in the calculation of the potential surface used in all previous calculations for this reaction. The new calculations using the improved potential surface now align closely with the CSR experiment.

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