Question: what is a white hole

Nicolas Labrosse answered on 20 Jun 2017:

Good question! I’m not enough of a specialist on this, but I would say it’s the reverse of a black hole. What is a black hole then? It’s an astrophysical object that has such a strong gravitational pull that nothing can escape from it, not even light. So, matter will fall on a black hole, with no light being able to escape it – hence its name.
Black holes can be formed under relatively well-understood processes, for instance when a massive star dies. They are quite well documented, and there is enough observational evidence that shows black holes exist in the universe.
A white hole would then be something on which nothing could fall, and which would emit a huge amount of light. There is no known physical process that could produce a white hole under standard physics conditions, and there is no observational evidence that convincingly shows white holes exist, so this is more a hypothetical, theoretical object at this stage.
But science will never stop surprising us… so who knows? Perhaps white holes can be found in the Universe? That’s why we need new enthusiastic young people to study physics (and maths) at University and then make science progress!