Scientists recreate universe's first molecule to solve 14-billion-year-old mystery

Irish Independent

05-08-2025

The universe was unimaginably hot and dense immediately after it formed about 13.8 billion years ago, and cooled down seconds later to form the first elements, hydrogen and helium, albeit in a completely ionised form.
It then took another 380,000 years for the temperature in the early universe to drop enough for neutral atoms to form, by combining with free electrons to pave the way for the first chemical reactions.
The first molecule created this way is thought to be helium hydride ion (HeH+), formed from a neutral helium atom and ionised hydrogen.
Helium hydride's origin also marked the beginning of a chain reaction that led to the formation of molecular hydrogen (H2), which is by far the most common molecule in the universe, scientists said.
Although the infant universe at this point was transparent due to the binding of free electrons, there were still no light-emitting objects, such as stars.
Researchers found that this helium hydride molecule helped cool the universe over a process lasting several hundred million years before the first stars ignited.
Stars are powered by nuclear fusion. However, for any early contracting gas cloud of a protostar to collapse to the point where nuclear fusion can begin, heat must be dissipated through collisions between atoms and molecules.
But below 10,000C, this process becomes ineffective for the dominant hydrogen atoms.
So researchers have long considered helium hydride ions as a potentially important candidate for cooling in the formation of the first stars.
New research, published in the journal Astronomy and Astrophysics, used a special ultra-cold lab setup to mimic conditions from over 13 billion years ago that led to the formation of these molecules.
ADVERTISEMENT
Using the Cryogenic Storage Ring instrument at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, scientists superimposed HeH+ ions stored in a 35-metre-diameter storage ring for up to just a minute at a few kelvins (-267C) with a beam of neutral hydrogen atoms.
They studied how the collision rate varied with temperature and found that, contrary to earlier predictions, the rate at which this reaction proceeds does not slow down with decreasing temperature.