In the first three minutes of the universe after the big bang, nuclear fusion formed essentially only the elements hydrogen and helium. This process, known as big bang nucleosynthesis (BBN), generated insignificant amounts of heavier elements. There were no stars or galaxies yet.

Immediately after BBN, the extreme heat of the early universe prevented free electrons from combining with hydrogen and helium nuclei to form neutral atoms. As soon as a nucleus captured an electron, the heat of the universe would immediately rip the electron back off (through collisions either by high energy photons or by energetic electrons). Only after about 400,000 years of expanding did the universe cool down enough to allow nearly all the free electrons and nuclei to combine, thereby forming neutral hydrogen and helium atoms. There were still no stars or galaxies.

Out of giant clouds of atomic hydrogen and helium, the first stars ultimately formed. hublot replica replica watches replica watches uk


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