In the depths of space and the hearts of galaxies lurk monsters: holes in space that drag passers-by to certain doom if they venture too close. That’s the popular image of black holes, but these ravenous cosmic beasts are proving to be even more fascinating – and fearsome – than their reputation suggests.

The concept of an object so massive that not even light can escape the pull of its gravity was first mooted way back in 1783. Geologist John Michell wrote in a letter to the Royal Society that if a star were massive enough, “a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light… all light emitted from such a body would be made to return towards it by its own proper gravity”.

That insight went neglected for more than a century, because physicists came to believe that light could not be deflected by gravity. However, Einstein’s 1915 theory of general relativity predicted that such deflection could in fact occur – a prediction subsequently borne out by experiment. That meant the light-capturing bodies suggested by Michell were actually possible – although Einstein himself was reluctant to accept that such a weird object could really exist.

The term “black hole” was coined by the quantum physicist John Wheeler, who also gave us “wormhole”. Theoretical physicists spent decades demonstrating that black holes really were consistent with Einstein’s ideas and working out how they should behave. And then the hunt was on to find one.

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