An Etymological Dictionary of Astronomy and Astrophysics

The helium element created in the → early Universe, around 3 minutes after the → Big Bang, when the temperature dropped to 10⁹ degrees; in contrast to the helium being synthesized in stars.

Based on observations of helium → emission lines in → H II regions of metal-poor dwarf galaxies (→ metal-deficient galaxy), the primordial ⁴He → chemical abundance (by mass) is estimated to be Y_P = 0.24672 ± 0.00017. Moreover, using observations of a near-pristine → intergalactic cloud, a value of
0.250 ^+0.033_-0.025 has been reached
(Cooke & Fumagalli, 2018, Nature Astronomy, 2, 657). The theoretical He abundance predicted by → Big Bang nucleosynthesis is
0.24709 ± 0.00017 (Pitrou et al., 2018, arXiv:1801.08023).

See also: → primordial; → helium.