How to think about... Black holes

2019-03-15 07:12:01

Dimitar Todorov/Alamy Stock Photo By Daniel Cossins THE starting point is familiar enough. “A black hole is a part of space-time so incredibly warped, and where gravity becomes so incredibly intense, that nothing can escape, not even light,” says physicist Pedro Ferreira at the University of Oxford. That is also where the problems begin. Black holes are cast-iron predictions of general relativity, Einstein’s peerless theory of gravity, and yet they stretch it to breaking point. Its equations fail catastrophically at a black hole’s centre, known as its singularity, where the warping of space-time simply goes off the scale. “Everything you calculate goes to infinity,” says Ferreira. “It has no meaning.” Even Einstein thought that black holes were too absurd to be real. They emit no light, so we cannot see them. Yet we infer their presence from their influence on nearby matter as they suck in gas and dust and stars, the contortions of which produce awesome light shows. In 2015, when we detected gravitational waves for the first time, the observed ripples in space-time matched the predicted signal from two black holes spiralling into one another and merging. Actually, black holes are rather common. Space is pockmarked with ones formed when over-massive stars collapse and die: