Key Ideas

The Special Theory of Relativity: This theory, published by Einstein in 1905, describes how measurements of lengths and durations of time depend on the motion of an observer and can appear different to different observers.

The General Theory of Relativity: Published by Einstein in 1915, this is a theory of gravity. Any massive object causes space to curve 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.

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Black Holes: If a stellar corpse has a mass greater than about 2 to 3 M, gravitational compression will overwhelm any and all forms of internal pressure.

Observing Black Holes: Black holes have been detected using indirect methods.

Gamma-ray Bursts: Short, intense bursts of gamma rays are observed at random times coming from random parts of the sky.

Properties of Black Holes: The entire mass of a black hole gets quickly concentrated in a nearly infinitely dense singularity.