white hole

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A hypothetical space-time singularity similar to a black hole except that matter and energy are emitted rather than absorbed at the event horizon. Though theoretically possible according to general relativity, the existence of isolated white holes is generally considered to be physically impossible because they would violate the second law of thermodynamics, which prohibits the spontaneous reversal of many natural processes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A theoretically possible but physically highly unlikely singularity from which matter and energy are able to escape; the antithesis of a black hole.