ASTRON 2B03 Lecture Notes - Lecture 12: Helium-3, Before Present, Universe Today
10 Apr 2018
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Astronomy 2b03 lecture: combine 2p + 2n to make one nucleus of a helium atom. This initial period of big-bang nucleosynthesis only lasts a few minutes. All the gas is expanding and cooling o , so after a while the particle interactions stop. What"s left after this stage is a gas mixture of: hydrogen (9 atoms out of 10) 75% by mass, helium (1 atom out of 10) - radiation (photons) Lithium was tiny part of 1%, it was helium 3 and 4 combined. Hot ionized gas in the early universe, have electrons and protons (neg and pos) Photons of light whenever they encounter an electron will bounce o of it and scatter. But now, as the universe expands, this hot gas gets cooler and more spread-out (less dense). Eventually a very important event happens: the electrons latch on to the nuclei (protons) to produce normal atoms atom of hydrogen, have a sea of neutral particles and photons forms neutral.
