White hole

WHITE HOLE

In general relativity, a white hole is a hypothetical region of spacetime which cannot be entered from the outside, although matter and light can escape from it. In this sense, it is the reverse of a black hole which can only be entered from the outside and from which matter and light cannot escape.

White holes are considered as one of the outlet for another universe. White holes expel out mass and energy. 

White holes are door  for entering new universe. White holes combined with black hole can form a wormhole. Some scientists believed on multiple which binds each others by black hole and white hole. 

It is reverse of black hole. As any object enter in black hole nearly at speed of light, in case of worm hole it will thrown out in new universe or at distant place with almost speed of light. 

The possibility of the existence of white holes was put forward by Russian cosmologist 

Iron Nogovic. White holes still are hypothetical 

Here, "maximally extended" refers to the idea that the spacetime  should not have any "edges": for any possible trajectory of a free-falling particle  in the spacetime, it should be possible to continue this path arbitrarily far into the particle's future, unless the trajectory hits a singularity like the one at the center of the black hole's interior. In order to satisfy this requirement, it turns out that in addition to the black hole interior region which particles enter when they fall through the event horizon from the outside, there must be a separate white hole interior region, which allows us to extrapolate the trajectories of particles which an outside observer sees rising up away from the event horizon. For an observer outside using  sch co -ordinates , infalling particles take an infinite time to reach the black hole horizon infinitely far in the future, while outgoing particles which pass the observer have been traveling outward for an infinite time since crossing the white hole horizon infinitely far in the past (however, the particles or other objects experience only a finite time between crossing the horizon and passing the outside observer). There is little evidence of white holes, though. The black hole/white hole appears "eternal" from the perspective of an outside observer, in the sense that particles traveling outward from the white hole interior region can pass the observer at any time, and particles traveling inward which will eventually reach the black hole interior region can also pass the observer at any time.

White holes are extension of Einstein field equation with no charge and no rotation of black holes.