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| Artist's concept of black hole with torus and jets. |
Black holes are objects with such immense gravity concentrated in such a small volume that nothing, not even light, can escape their grasp. Scientists have speculated about such bizarre objects since the 1700s, long before Einstein's theory of gravity (General Relativity) gave further credence to their existence.
Although Einstein's equations predicted their reality, he never thought that such bizarre objects could actually exist in nature. But the advent of X-ray astronomy in the 1960s started providing astronomers with data that hinted at their existence. Since then, radio and optical telescopes, as well as X-ray and gamma-ray satellites, have all provided incontrovertible evidence for black holes. We now know that they not only exist, but are common in our Universe. Black holes have now moved from the realm of theoretical speculation to observed fact.
More exciting, orbiting X-ray telescopes have provided tantalizing evidence that black holes drag space itself, like a bowling ball spinning in molasses, just as Einstein's equations predict. Observers have also seen evidence of time slowing and of matter whizzing around black holes at near light speed, as General Relativity predicts.
Black holes are thus the ultimate laboratory to test our understanding of gravity in extreme conditions that we cannot possibly duplicate on Earth. What happens to matter and energy as it moves closer to a black hole and crosses the event horizon, the theoretical boundary from inside of which nothing can escape? Does time really come to a standstill? Will we see a breakdown in General Relativity in these environments of extreme gravity? General Relativity makes specific predictions about matter and energy close to a black hole. If, upon closer scrutiny, we see the slightest deviation between theory and observation, we will understand limitations in Einstein's equations. Beyond Einstein missions such as Constellation-X will make these observations possible.
Newton's theory of gravitation represented a giant leap in our understanding of physics. Similarly, General Relativity revolutionized physics two centuries later. By truly understanding what happens at the very edge of a black hole, we may be poised at the threshold of another revolution in physics that will take us Beyond Einstein.
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