3
$\begingroup$

This seems to be a chicken and egg problem, the sun begins shining due to hydrogen becoming helium, but it's odd that there was no helium initially without the stars.

Is my logic flawed?

(Note: First year astronomy student)

Improve this question
$\endgroup$
2
  • $\begingroup$ The helium abundance in the universe has hardly changed since after nucleosynthesis in the big bang which created about 23% He by mass. The figure now in the interstellar medium of our Galaxy is estimated to be around 25%. $\endgroup$
    – ProfRob
    Mar 18, 2015 at 10:40
  • $\begingroup$ This may not be what you intended by this question, but the object that would become the sun was 'shining' before the p-p chain was able to activate in the core, due to gravitational contraction. This proto-sun of course developed from a cloud with ~24% He, so He existed before the sun on all accounts. $\endgroup$
    – ShroomZed
    Aug 1, 2019 at 13:20

1 Answer 1

Reset to default
4
$\begingroup$

The Big Bang theory predicts that (depending what assumptions you choose) the initial elements were formed from 10 seconds to 20 minutes after the Big Bang.

The initial elements were

  • mostly hydrogen

  • some deuterium

  • some helium-3 and helium-4

  • a little lithium-7

  • a couple of unstable isotopes that decayed to lithium-7 or helium-3.

As the linked Wikipedia article says

Essentially all of the elements that are heavier than lithium and beryllium were created much later, by stellar nucleosynthesis in evolving and exploding stars.

So the answer to your question is: the Helium came first.

Improve this answer
$\endgroup$
4
  • $\begingroup$ Correction: most helium came first. $\endgroup$
    – Florin Andrei
    Mar 18, 2015 at 18:01
  • $\begingroup$ @Florin Not sure what you mean; can you clarify? The answer says the helium came first, before stars. 75% of BBN output was hydrogen by mass. $\endgroup$
    – andy256
    Mar 18, 2015 at 21:22
  • $\begingroup$ Right. I'm just saying, some of the helium that exists today, a fraction of it, was made by stars, much later after the Big Bang. $\endgroup$
    – Florin Andrei
    Mar 18, 2015 at 23:11
  • $\begingroup$ @Florin Ok. Interestingly, most of the helium on Earth comes from radioactive decay of heavy elements. $\endgroup$
    – andy256
    Mar 18, 2015 at 23:51

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .