ABOUT BLACKHOLE

In general relativity, a black hole is a region of space in which the gravity well is so deep that gravitational time dilation halts time completely forming an event horizon, a one-way surface into which objects can fall, but out of which nothing can come. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black-body in thermodynamics.Quantum analysis of black holes shows them to possess a temperature and Hawking radiation.
Despite its invisible interior, a black hole can reveal its presence through interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Alternatively, one can see gas falling into a relatively small black hole, from a companion star. This gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and earth-orbiting telescopes. Such observations have resulted in the scientific consensus that, barring a breakdown in our understanding of nature, black holes exist in our universe.
The No hair theorem states that, once it settles down, a black hole has only three independent physical properties: mass, charge, and angular momentum.Any two black holes that share the same values for these properties, or parameters, are classically indistinguishable.
These properties are special because they are visible from outside the black hole. For example, a charged black hole repels other like charges just like any other charged object, despite the fact that photons, the particles responsible for electric and magnetic forces, cannot escape from the interior region. The reason is Gauss's law, the total electric flux going out of a big sphere always stays the same, and measures the total charge inside the sphere. When charge falls into a black hole, electric field lines still remain, poking out of the horizon, and these field lines conserve the total charge of all the infalling matter. The electric field lines eventually spread out evenly over the surface of the black hole, settling down to a uniform field-line density on the surface. The black hole acts in this regard like a classical conducting sphere with a definite resistivity.
Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, far away from the black hole. Likewise, the angular momentum can be measured from far away using frame dragging by the gravitomagnetic field.
When a black hole swallows any form of matter, its horizon oscillates like a stretchy membrane with friction, a dissipative system, until it settles down to a simple final state. This is different from other field theories like electromagnetism or gauge theory, which never have any friction or resistivity, because they are time reversible. Because the black hole eventually settles down into a final state with only three parameters, there is no way to avoid losing information about the initial conditions: The gravitational and electric fields of the black hole give very little information about what went in. The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including the total baryon number, lepton number, and all the other nearly conserved pseudo-charges of particle physics. This behavior is so puzzling, that it has been called the black hole information loss paradox.
The loss of information in black holes is puzzling even classically, because general relativity is a Lagrangian theory, which superficially appears to be time reversible and Hamiltonian. But because of the horizon, a black hole is not time reversible: matter can enter but it cannot escape. The time reverse of a classical black hole has been called a white hole, although entropy considerations and quantum mechanics suggest that white holes are just the same as black holes.
The no-hair theorem makes some assumptions about the nature of our universe and the matter it contains, and other assumptions lead to different conclusions. For example, if Magnetic monopoles exist, as predicted by some theories, the magnetic charge would be a fourth parameter for a classical black hole.