Question

what happens to stars after millions (or billions) of years? they continue to shine bright. they die down and go extinct.

Explanation:

Stars have a life - cycle. After millions or billions of years, when their nuclear fuel is exhausted, they die down and eventually go extinct. They do not continue to shine bright indefinitely as they rely on nuclear fusion reactions for their energy which will come to an end.

Answer:

They die down and go extinct.