Stars are usually in equilibrium, which means they are making enough energy to push their mass outward against the force of gravity. When the star runs out of fuel to make energy, gravity takes over. Gravity pulls the center of the star inward very quickly. A white hole, in general relativity, is a hypothetical region of space time which cannot be entered from the outside, but from which matter and light may escape. In this sense it is the reverse of a black hole, which can be entered from the outside, but from which nothing, including light, may escape.
However, it is theoretically possible for a traveler to enter a rotating black hole, avoid the singularity, and travel into a rotating white hole which allows the traveler to escape into another universe. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein equations has a white hole region in its past. However, this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed. Like black holes, white holes have properties like mass, charge, and angular momentum. They attract matter like any other mass, but objects falling towards a white hole would never actually reach the white holes event horizon. The white hole event horizon in the past becomes a black hole event horizon in the future, so any object falling towards it will eventually reach the black hole horizon. They are, predicted as a possible other end of a black hole that has a worm hole through space, ut black holes are most likely just a point in space without an other side. A white hole is the theorized time reversal of a black hole. The event horizon of a black hole attracts matter, so event horizon of a white hole ejects matter even though the white hole itself still attracts matter. The main difference between the two is the action of the event horizon. As you can see, this is what a black hole and a white holes are