The Special Theory of Relativity: This theory, published by Einstein in 1905, is based on the notion that there is no such thing as absolute space.

-The speed of light is the same to all observers, no matter how fast they are moving.

-An observer will note a slowing of clocks and a shortening of rulers that are moving with respect to the observer. This effect becomes significant only if the clock or ruler is moving with a speed near the speed of light.

The General Theory of Relativity: Published by Einstein
in 1915, this is a theory of gravity. Any massive object causes space to become curved and time to slow down, and these effects manifest themselves as a gravitational force. These distortions of space and time are most noticeable in the vicinity of large masses or compact objects.

-The general theory of relativity is our most accurate description of gravitation. It predicts a number of phenomena, including the bending of light by gravity and the gravitational red shift, whose existence has been confirmed by observation and experiment.

-The general theory of relativity also predicts the existence of gravitational waves, which are ripples in the overall geometry of space and time produced by moving masses. Gravitational waves have been detected indirectly, and specialized antennas are under construction to make direct measurement of the gravitational waves from cosmic cataclysms.

Black Holes: If a stellar corpse has a mass greater than about 3 M0' gravitational compression will overwhelm any and all forms of internal pressure. The stellar corpse will collapse to such a high density that its escape speed exceeds the speed of light. The corpse then contracts rapidly to a single point called a singularity, where all of the mass is located.

-The singularity is surrounded by a surface called the event horizon, where the escape speed equals the speed of light. Nothing-not even light-can escape from inside the event horizon.

Properties of Black Holes: A black hole-a singularity surrounded by an event horizon-has only three physical properties: mass, electric charge, and angular momentum.

-A rotating black hole (one with angular momentum) has a region called the ergo sphere around the outside of the event horizon. In the ergo sphere, space and time themselves are dragged along with the rotation of the black hole.
Black Holes in Binary Systems: Some binary star systems are thought to contain a black hole. In such a system, gases captured from the companion star by the black hole emit detectable X rays.

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