An international team of astronomers has pinned down the amount of helium created in the first five minutes after the Big Bang with unprecedented accuracy. By analyzing 15 exceptionally pristine galaxies with the Large Binocular Telescope, they reduced the uncertainty in this primordial abundance to 0.5% — three times better than earlier efforts. The findings appear in five papers in The Astrophysical Journal.
The selected galaxies act as cosmic time capsules, having undergone little chemical change over nearly 13.8 billion years. Using spectrographs developed at Ohio State University, the team examined more than 10 helium and 15 hydrogen spectral lines simultaneously, allowing them to correct subtle measurement errors that mattered once the target was sub-1% precision.
The improved helium abundance provides a direct test of the Standard Model of physics. Because the amount of helium formed depends on the physical conditions in the early Universe, the team used their measurement to calculate the number of neutrino families present at that time. As co-author Evan Skillman of the University of Minnesota put it, this is "a physics experiment on a grand scale" and one of the biggest findings of his 40-year career.