Black holes hold many secrets of space and time.

Some of the great mysteries about black holes, and the nature of gravity itself, will come under the scrutiny of NASA's next generation of space telescopes and probes. Here is a sampling of the questions they will probe.

What happens to space and time near a black hole?  
At the edge of a black hole time should appear to slow to a halt, and if the black hole is spinning, the very fabric of space should be twisted, carrying any nearby objects around with it. Scientists can probe this hostile environment by observing nearby matter that spirals in towards the hole. The atoms in the matter emit X-ray light, whose vibrations serve as clocks that can help us precisely measure the flow of time and the distortion of space. This light will be collected by NASA's Constellation-X mission, revealing for the first time what conditions are like at the very edge of a black hole.

How do black holes create such powerful jets of energy?
A black hole is the most efficient and powerful engine in the universe: Somehow, much of the matter falling towards a black hole is instead propelled outward at close to the speed of light – an effect that came as a complete surprise to astronomers. These jets of matter seem to start near the edge of a black hole, and are probably set in motion by the tremendous magnetic fields produced by the spinning black hole. NASA's Constellation-X will probe the interaction between infalling matter, magnetic fields, and black holes, allowing scientists to understand how such powerful rays of matter could be created.

What role do black holes play in the unfolding universe?
It is now thought that almost every galaxy has a giant black hole at its center. These black holes were probably present when the galaxy itself was formed and may have aided in the galaxy's formation. If this is true, then black holes may play a pivotal role in the formation of conditions in the universe that are necessary for life. The very earliest galaxies in the universe cannot be observed with existing telescopes, but that is about to change: NASA's James Webb Space Telescope will be able to glimpse the earliest galaxies in the process of formation – galaxies whose light will have taken 13 billion years to reach Earth – and the Constellation-X mission will observe the giant black holes that live within them.

Do black holes send ripples of gravity through space?   Einstein's theory of gravity predicts that black holes can send ripples of gravity through the fabric of space itself. NASA's LISA space mission, planned for launch within a decade, should be able to detect these waves of gravity – acting as a kind of cosmic "seismograph." High on the cosmic Richter scale of quakes should be the collision of two black holes, or of a black hole with another star. LISA's ability to detect colliding black holes is only the first step in its voyage of discovery. Gravity waves are a completely new tool with which to explore the universe. Gravity-wave astronomy complements traditional astronomy, and can reveal events in the universe that could not be explored using light and conventional telescopes.

Can we see a black hole being formed?
About once a day, there is a dazzling flash in the sky. It is not a flash of visible light, but a flash of gamma rays, a high-energy form of light even more powerful than X-rays. These flashes, called gamma-ray bursts, come from the tremendous explosion of a star going "supernova." The event is the last gasp of a star's core before it collapses into a black hole. The bursts are being detected by NASA's HETE space telescope, which beams the location of the flash to other telescopes on the ground and in space. From these telescopes we see the fading glow of the dying star, and witness the birth of a black hole. NASA's new Swift mission will spot gamma-ray bursts more quickly, allowing the first few seconds of a black hole's life to be observed in detail.

What happens inside a black hole?
The only way to answer this question is by developing a better, more fundamental theory of space, time, and matter. Unfortunately, Einstein's theory of gravity – which gave us the idea of black holes in the first place – does not accurately predict what happens at the very smallest scales of distance. For example, the atoms in our body all contain electrons, yet electrons are so small and so dense that they ought to form black holes. Obviously, they don't. Why not? If new theories of physics, such as "string theory," are correct, then there may be additional dimensions of space beyond the three dimensions we see; these extra dimensions may be important in explaining the behavior of matter at very small scales of distance, including what happens at the center of a black hole.