What is a white hole?
The concept of a white hole only appears as part of the vacuum solution to Einstein’s field equations that are used to describe a Schwarzschild wormhole. A wormhole is a black hole on one end, drawing in matter, and a white hole on the other to emit matter. Schwarzschild wormholes are unstable. They collapse as soon as they form. Also, wormholes are only a solution to the Einstein field equations in a vacuum where no matter interacts with the hole. Real black holes are formed by the collapse of stars, but white holes shrink from matter so they could not exist in connection with true black holes because the presence of matter would cause them to collapse.