MPIK experiments found helium hydride ions react at nearly constant rates even at temperatures just a few kelvins above absolute zero, overturning long-standing models that predicted a sharp slowdown in the early universe.
At Heidelberg’s 35-meter Cryogenic Storage Ring, researchers stored HeH+ for up to 60 seconds and collided it with neutral deuterium, a proxy that closely mimics the key primordial reaction with hydrogen.
The measurements and matching new calculations indicate the reaction is barrierless, while also pointing to an error in a widely used potential energy surface that had understated low-temperature reaction rates.
Because HeH+ formed about 380,000 years after the Big Bang and fed chemistry leading to molecular hydrogen, faster destruction of the ion could force a re-evaluation of how primordial gas cooled and the first stars formed.
If the universe's first chemical reaction was faster than believed, must we rewrite the story of how the very first stars were born?
How does this discovery change what astronomers search for with the James Webb Telescope?
Breakthrough in HeH⁺ Reaction Rates at Near-Absolute Zero Reshapes Primordial Star Formation Models
Overview
The report highlights how a neutral helium atom and an ionized hydrogen nucleus combine to form the helium hydride ion (HeH⁺), the universe’s oldest molecule. HeH⁺ plays a crucial role in the cosmic chain reaction that leads to the formation of molecular hydrogen (H₂), both of which are essential for the birth of the first stars. Recent experiments reveal that HeH⁺ reactions remain efficient even at near-absolute zero, challenging previous theories. This discovery reshapes our understanding of how early gas clouds cooled and collapsed, making star formation in the early universe more efficient than previously thought.