The one thing that doesn't get trapped by black holes is gravity... which in turn can be considered a form of energy.
What Hawking proposed back in the mid 70's as I recall (and now known as
Hawking Radiation) is a marriage of two areas of physics (quantum mechanics and general relativity) to provide a solution for one of the oldest laws in physics... conservation of energy.
As most people who have heard of black holes know,
nothing can escape them, not even light. But this concept troubled physicists because this idea lead to loss of energy. The relativistic math of black holes was very straight forward and became evident with the
Schartzschild Solution*, but that left a lot of other questions unanswered. Infact, the name
Black Hole was originally a term of ridicule towards people that believed in these objects.
What was put forward by Hawking was based on virtual particles from quantum theory in which everywhere in the universe particle-pairs (a particle and an antiparticle) pop into and out of existence**. Hawking realized that at the event horizon*** of a black hole the gravitational tidal forces could be so great as to separate these virtual particles from each other. Most of the time, both particles get swallowed up by the black hole, but every so often half of a virtual pair might escape. The loss of that particle translates into a loss of energy for the black hole. The energy from the black hole was transmitted by gravity to the virtual pair of particles and was lost when part of the pair escaped. The particle being given off from the black hole is
Hawking Radiation.
Hawking theorized that if this happened enough, the black hole would eventually lose so much energy that it would evaporate completely.
Please note that the particles in Hawking Radiation
do not have a causal path**** back to the black hole itself. Because of this, no information from a black hole escapes.
I think that covers most of the information requested without having to get into the mathematics of all this (which is really great, and how I fell in love with mathematics, and specifically differential geometry and differential topology to begin with).
* The Schartzschild Solution is an application of general relativity centered around a spherical mass... which as I recall was one of the first applications of mathematics developed by Levi-Civitia to provide the ability to apply general relativity at all. Before Einstein's theory of gravity was released in 1916, the area of differential geometry in mathematics had changed very little since the mid 19th century, mainly with the work of Riemann. General relativity revitalized differential geometry in many ways.
** Virtual pairs are best thought of as a single particle traveling in a circular path in space-time, which while moving forward in time it appears as a particle, and which while moving backwards in time it appears as an antiparticle.
*** The event horizon of a black hole is a sphere with a radius equivalent to twice the mass of the black hole. What was noticed in the Schartzschild Solution was that if the radius of a massive body became smaller than this Schartzschild Radius, the body would continue to collapse without end... this part of the solution produces a singularity in local space-time which is outside what the mathematics can deal with (which is why we don't know much about what happens in a black hole).
**** An important aspect of space-time singularities is that they are isolated from the rest of the universe. This means that there are no causal paths back inside of an event horizon. This is generally put forward as there can be no naked singularities (where the singularity is the black hole itself). This idea was altered slightly with Big Bang Theory because the Big Bang is a singularity and everything has a causal path back to it.
Suggested Reading and References:
- Gravitation by Charles Misner, Kip Thorne and John Wheeler
- Large Scale Structure of Space-Time by Stephen Hawking and GFR Ellis
- Gravitational Curvature by Theodore Frankel
- Techniques of Differential Topology in Relativity by Roger Penrose
- The Geometry of Physics by Theodore Frankel
For full disclosure, Professor Frankel was a professor at UCSD while I was attending. I have met (but do not know personally) both Professor Thorne and Professor Penrose... just in case someone thinks any of these suggestions are to push book sales.
