What happens for a star to enter old age?

Because the interstellar medium is 97% hydrogen and 3% helium, with trace amounts of dust, etc., a star primarily burns hydrogen during its lifetime. A medium-size star will live in the hydrogen phase, called the main sequence phase, for about 50 million years. Once hydrogen fuel is gone, the star has entered “old age.”

for a star to start the process of become an old star it has to burn all the hydrogen in the star.

Explanation:

I hope this helps if not sorry :(

Have a good day :)

Stay motivated

the correct answer is boyle

let that person have a turn to speak : )