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The Question

(Submitted January 08, 1998)

Which came first in the formation of the universe as we see it today? Stars or galaxies? I've heard that many books have discussed this topic, but many say that it could have been either way.

The Answer

You've asked a very interesting question that I'm afraid I can't give you a good answer to. This is a sort of chicken-and-egg question that has not been scientifically resolved yet. People who work on the dynamics of galaxy formation say that the galaxy-mass gas clouds should form first. But in the "earliest" galaxies we see, the gas contains heavy elements that seem to have come from a first generation of stars. The big bang (by current theory) should have produced only hydrogen, helium, and a trace amount of lithium. So where did these first generation stars form? We don't have the answer, but it's one of the things that astrophysicists are trying to resolve.

Thanks for your question.

Eric Christian
for Ask an Astrophysicist

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