Composition of the Early Universe:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jul 19, 2019.

  1. paddoboy Valued Senior Member

    Messages:
    27,543
    https://phys.org/news/2019-07-imply-higher-abundance-helium-hydride.html

    New measurements imply dramatically higher abundance of helium hydride ions in the early universe:

    Physicists report the first laboratory measurements of electron reactions with helium hydride ions in the cryogenic storage ring CSR at the Max Planck Institute for Nuclear Physics in Heidelberg. At temperatures down to 6 K, the reaction rates destroying the molecule were found to be significantly lower compared to previous measurements at room temperature. This translates into a strongly enhanced abundance of this primordial molecule acting as a coolant for first star and galaxy formation in the early universe.

    Just three minutes after the Big Bang, the chemical composition of the universe was settled: 75 percent hydrogen, 25 percent helium, and trace amounts of lithium, all created by primordial nucleosynthesis. However, in this early state, all matter was fully ionized, consisting of free bare nuclei and a hot electron gas, a "foggy" plasma for the cosmological background radiation.

    About 400,000 years later, the expanding universe cooled down to a level where electrons and nuclei started to combine into neutral atoms. Space became transparent, but no stars were yet born; thus, this era is called the "dark ages." As the temperature dropped further, collisions of neutral helium with still abundant free protons formed the first molecule—the helium hydride ion (HeH⁺), which marks the dawn of chemistry. HeH+ and other early molecular species played an essential role in cooling primordial gas clouds via infrared emission, a necessary step for star formation.
    more at link.....

    the paper:

    https://science.sciencemag.org/content/early/2019/07/17/science.aax5921


    Quantum-state–selective electron recombination studies suggest enhanced abundance of primordial HeH+

    Abstract:
    The epoch of first star formation in the early universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a dramatic decrease of the electron recombination rates for the lowest rotational states of HeH+, compared to previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.
     

Share This Page