In a monumental breakthrough, scientists have recreated the universe’s first molecule, helium hydride (HeH⁺), solving a puzzle that has baffled astronomers for over 13 billion years. The discovery could change how we understand the formation of stars in the early universe.
The Formation Of The First Molecules After The Big Bang
Immediately after the Big Bang, which occurred around 13.8 billion years ago, the universe was an extremely hot and dense place. However, in a matter of seconds, it cooled enough for the first elements to form—primarily hydrogen and helium. At this point, these elements were completely ionized, with free electrons and atomic nuclei floating around.
It wasn’t until nearly 380,000 years later that the universe cooled enough for neutral atoms to form through recombination, setting the stage for the first chemical reactions to take place.
Helium hydride (HeH⁺), the first molecule ever to form, came into existence when a neutral helium atom combined with an ionized hydrogen nucleus. This marked the beginning of a chemical chain reaction that ultimately led to the creation of molecular hydrogen (H₂), which remains the most abundant molecule in the universe.
The Role Of Helium Hydride In Star Formation
After the initial recombination, the universe entered what is known as the “dark age” of cosmology. During this time, while the universe became transparent, there were no light-emitting objects such as stars. It would take several hundred million years for the first stars to form. However, molecules like HeH⁺ and H₂ were essential to the process that led to the birth of stars.
As a protostar forms, a gas cloud collapses under gravity. This collapse generates heat, which must be dissipated for nuclear fusion to begin. At temperatures above 10,000°C, this dissipation was ineffective for hydrogen atoms.
The process only worked effectively with molecules that could emit energy through rotational and vibrational movements. HeH⁺, with its distinct dipole moment, was especially effective at lower temperatures.
Credit: W. B. Latter (SIRTF Science Center/Caltech) and NASA
New Experiments Challenge Old Assumptions
Researchers at the Max-Planck Institute for Nuclear Physics (MPIK) in Heidelberg, Germany, have now successfully recreated the HeH⁺ reaction under conditions simulating the early universe. The team conducted their experiment at the Cryogenic Storage Ring (CSR), an advanced facility that allows scientists to study molecular and atomic reactions in ultra-cold environments. They exposed HeH⁺ ions to deuterium, a hydrogen isotope, in a super-cooled setting of just a few kelvins (about -267°C).
The experiment revealed surprising results. Contrary to earlier predictions, the reaction between HeH⁺ and deuterium did not slow down as the temperature decreased. Instead, the rate of the reaction remained nearly constant, challenging long-held assumptions in cosmology.
“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 from MPIK.