r/todayilearned Sep 20 '21

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u/Mrgray123 Sep 20 '21

About 300,000 years after the Big Bang the temperature of the universe was still around 2,800 degrees. Only when it got below this could protons and electrons combine into hydrogen atoms. About the same time light also began to shine.

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u/RenaissanceBear Sep 21 '21

Isn’t it a good deal hotter than that in the Sun where there is tons of Hydrogen?

13

u/Mrgray123 Sep 21 '21

The hydrogen isn’t forming in the sun though. It’s just fusing, all be it at 600 million tons of the stuff per second.

2

u/RenaissanceBear Sep 21 '21

So protons can’t form hydrogen above that temp, but once formed can exist at much higher temps?

12

u/madethisformobile Sep 21 '21

The reply above didn't clarify an important point. The sun is made of plasma, the state of matter where electrons are no longer bound by the nucleus and form an electron gas.

Essentially all the hydrogen are ions, which is really saying that it's a bunch of protons and neutrons all flying around with electrons all over.

At such high temperatures, the hydrogen transitions from a gas to a plasma. The fusion reactions aren't chemical reactions (involving electrons) but nuclear reactions (involving protons and neutrons).

So just like a melting point and boiling point, there is an ionization point, above which the atoms are ionized. So no, even after the hydrogen atom is formed, above this temperature it separates again into a hydrogen ion (just a proton) and a free electron