Shortly after the Big Bang, around 13.8 billion years ago, the universe was incredibly hot and dense. Within seconds, it cooled enough for elements like hydrogen and helium to form. However, it took about 380,000 years for temperatures to drop sufficiently for neutral atoms to appear. This crucial step allowed for the first chemical reactions to kick off.
Interestingly, the oldest known molecule is the helium hydride ion (HeH+), created from a neutral helium atom and an ionized hydrogen nucleus. This marked the beginning of a series of reactions that ultimately led to molecular hydrogen (H2), the universe’s most abundant molecule.
After this recombination, the universe entered a “dark age.” Although it became transparent, it lacked any light-generating stars for several hundred million years. Yet, simple molecules like HeH+ and H2 were essential in forming those first stars. For a gas cloud to collapse and ignite nuclear fusion, it needed to cool down. This cooling happens through collisions that excite atoms, allowing them to release energy as light. Below around 10,000 degrees Celsius, hydrogen atoms alone can’t cool effectively. Instead, molecules, particularly HeH+, play a vital role due to their ability to lose energy through rotation and vibration. Thus, the presence of HeH+ could have significantly impacted early star formation.
As HeH+ interacted with free hydrogen atoms, it transformed into a neutral helium atom and an H2+ ion, which then reacted with another hydrogen atom. This led to the creation of molecular hydrogen and a proton.
Recently, researchers at the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg made a breakthrough. They recreated the early universe’s conditions to study how HeH+ reacts with deuterium, a hydrogen isotope. Instead of forming H2+, the reaction produced an HD+ ion alongside a neutral helium atom.
This experiment was conducted at the Cryogenic Storage Ring (CSR), a unique facility simulating space-like conditions. Scientists stored HeH+ ions in this ring, allowing them to collide with deuterium atoms. Surprisingly, they discovered that the reaction rate remained constant even at lower temperatures, contrary to past expectations. Dr. Holger Kreckel from MPIK noted that this finding suggests these reactions were more crucial for the universe’s early chemistry than previously believed.
This work aligns with new theoretical insights by physicists, who found errors in earlier calculations of the potential surfaces used in modeling these reactions. The improved models now closely match the experimental results, paving the way for a deeper understanding of how the first stars formed.
Overall, understanding molecules like HeH+ and H2 is vital for unraveling the story of star formation. This research not only sheds light on cosmic history but also informs fields like astrophysics and cosmology, crucial for exploring the universe’s evolution.
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Stars; Astrophysics; Space Exploration; Dark Matter; Chemistry; Inorganic Chemistry; Physics; Optics
