6 days ago
New findings on universe's first molecule reveal bigger role in forming early stars
The universe's first molecule just surprised us again.
In a discovery that could rewrite our understanding of how the first stars formed, researchers at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have revealed unexpected behavior in helium hydride (HeH⁺), the earliest known molecule in the cosmos.
Contrary to long-standing predictions, HeH⁺ remained chemically reactive even at extremely low temperatures: conditions that mimic the early universe.
To test how this ancient molecule behaved just after the Big Bang, researchers recreated early-universe conditions at the Cryogenic Storage Ring (CSR) in Heidelberg.
The world's only facility of its kind, CSR simulates space-like environments just a few degrees above absolute zero.
By colliding stored HeH⁺ ions with a beam of neutral deuterium atoms, the team was able to observe the molecule's reaction rates at ultra-cold temperatures for the first time.
Formed shortly after the Big Bang, HeH⁺ is a simple molecule made from a helium atom and a proton. It marked the beginning of chemical bonding in the universe and laid the foundation for molecular hydrogen (H₂), the fuel that powers stars.
For decades, HeH⁺ has been assumed to play a passive role in the cooling processes that allowed protostars to condense and ignite. But new experimental results challenge that narrative.
Molecule that changed everything
The researchers found that instead of slowing down as the temperature dropped, the reaction between HeH⁺ and deuterium remained surprisingly constant. This contradicts earlier models, which predicted a steep decline in reactivity at low temperatures.
'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,' said Dr. Holger Kreckel of MPIK.
This matters because in the young universe, during the so-called 'cosmic dark ages' before stars began to shine, molecules like HeH⁺ played a key role in cooling the primordial gas.
Effective cooling is necessary for gas clouds to collapse under gravity and form stars.
Since hydrogen atoms alone can't release heat efficiently below 10,000°C, molecules with dipole moments like HeH⁺ were critical for shedding energy via radiation.
HeH⁺ also degrades through collisions with hydrogen atoms, producing ions that eventually lead to molecular hydrogen formation.
This chain of reactions was vital to star formation, and the new findings suggest HeH⁺ was far more active in that chemistry than previously thought.
Rethinking star formation chemistry
The MPIK team's results also exposed flaws in older theoretical models. Collaborating with theoretical physicist Yohann Scribano, researchers found a long-standing error in the potential energy surface used to predict HeH⁺ behavior.
Correcting this surface brought simulations in line with experimental data, sharpening our understanding of early-universe chemistry.
These findings, published alongside complementary theoretical work, reframe HeH⁺ as a central player in star formation rather than a passive bystander. '
The reactions of HeH⁺ with neutral hydrogen and deuterium, therefore, appear to have been far more important… than previously assumed,' Kreckel added.
As the oldest molecule in the universe, HeH⁺ just reminded us that the earliest chemistry still holds secrets with implications that stretch across time and space.
The study has been published in the journal Astronomy Astrophysics.
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