Spaghettification

Spaghettification is what happens to anything that falls too close to a black hole. The end nearer to the black hole is pulled harder than the far end, so the object is stretched out along the line towards it and squeezed in from the sides, into a long, thin strand. The effect is the same tide that raises the oceans on Earth. Near a black hole it becomes strong enough to tear apart a person, a planet or a star.

Why size matters

The stretch depends on how quickly gravity changes over the length of your body, and it grows with the inverse cube of distance: halve the distance and it is eight times stronger. On Earth, the difference between the pull on your head and your feet is about 0.0000055 metres per second squared, far too small to notice.

At the event horizon of a black hole with the mass of the Sun, only 2.9 kilometres from its centre, the stretch on a 1.8-metre person would be about 19.6 billion metres per second squared. Nobody would get that far in one piece. Stellar-mass black holes, up to about 30 times the Sun’s mass, tear things apart well before they reach the horizon.

A huge black hole is gentler. The horizon of one with 100 million times the Sun’s mass lies 295 million kilometres out, and there the stretch is only about 0.0000019 metres per second squared, less than Earth’s tide on you. You could cross that horizon without feeling the stretch. “If you have the choice, you want to fall into a supermassive black hole,” said Schnittman of NASA, who in 2024 made a simulation of a fall into a black hole of 4.3 million Suns, like the one at the centre of the Milky Way. His virtual camera crossed the horizon intact and was spaghettified 12.8 seconds later, about 128 000 kilometres from the centre.

Stars torn apart

Spaghettification has never been seen happen to anything as small as a person, but it is seen happening to stars. When a star strays too close to a supermassive black hole, it is drawn out into long streams of gas. In 1988 Rees calculated that about half of the star stays bound to the black hole and the rest is flung away. The gas falling back lights up as a brilliant flare. About 100 of these tidal disruption events were known by May 2024. Around the very largest black holes, above about 100 million Suns, a star like the Sun crosses the horizon before it can be torn apart and is swallowed whole without a flare.

When ESO reported it in 2020, AT2019qiz was the closest such flare yet recorded, just over 215 million light-years away in a spiral galaxy in Eridanus. A star of about the Sun’s mass lost about half of it to a black hole more than a million times heavier, and gas streamed away at up to 10 000 kilometres per second. In 2024 Nicholl and colleagues reported that, years later, the spot was erupting in X-rays about once every 48 hours.

The word

Stephen Hawking made the word famous in A Brief History of Time in 1988, with his image of an astronaut stretched like spaghetti. It is older than his book: it appears in print in 1977, in Nigel Calder’s The Key to the Universe.