Astronomers have measured that there is more helium in the universe than can be explained by the fusion in stars over the last 13 billion years. How do they think the extra helium got into the universe

From big bang and stars.

Explanation:

The extra helium got into the universe through big bang and fusion reaction that occur in stars. Our universe formed about 13.7 billion years ago with big explosion, this event is known as big bang. The fusion of hydrogen nuclei in the stars produces helium and energy so we can say that most of the extra helium got into the universe through fusion reaction that occur in the stars continuously.

it is very well related to a lot of things but with my limited knowledge i can confidently say that the answer is space.

i think the answer would be reserve.