Two forces oppose each other while a star is stable. The first is gravity pulling inward. What is the

other force?

the radiation pressure that has to push the star

Explanation:

In the stars there are two forces that act in the opposite direction.

- On the one hand there is the force of gravity that the star has to collapse

- On the other is the radiation pressure that has to push the star. This pressure comes from the radiation and velocity of the particles involved in nuclear reactions.