Black holes in space seem to be a recent phenomenon, yet Albert Einstein (1879-1955) predicted them in his theory of relativity in 1915.
They are the incredibly dense centres of dead stars.
Black holes appear black because their gravitational fields are so huge that even light can’t escape.
We find and measure black holes by calculating the orbits and other behaviors of nearby stars or gas clouds.
Black holes capture our imagination because we believe that should we fly a spacecraft anywhere near them they will capture us.
The Hubble Space Telescope has taken pictures of many suspected black holes.
One is the core of Galaxy NGC 4261.
Black holes are formed when a large star experience a gravitational collapse, usually at the end of its life, or when it becomes a supernova.
The idea of black holes was first proposed by geologist John Michell in a letter written to Henry Cavendish in 1783 to the Royal Society.