Space is pockmarked with ones formed when over-massive stars collapse and die: our galaxy alone holds perhaps 100 million of these smaller ones. Whatever they are, we think that black holes are really rather common. String theory offers one way, and might turn what we think are black holes into “fuzzballs” with no singularity and no event horizon – dense, star-like objects that essentially amount to a tangled ball of space-time string. A unified theory requires us to somehow reconcile the two, probably by reimagining space-time as only an approximate thing. General relativity says that when matter falls into a black hole, information is destroyed, but quantum mechanics says firmly it can’t be. To get down to the nitty-gritty of what happens there, you need to bring quantum theory into the picture – but quantum theory and general relativity famously don’t agree on anything. The event horizon is where the problems start.

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. Though we can’t see them, 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. General relativity’s equations fail catastrophically at a black hole’s centre, known as its singularity, where the warping of space-time simply goes off the scale.Įven Einstein thought that these cosmic objects were too absurd to be real. General relativity says that matter warps space and time black holes are simply very dense agglomerations of matter. We’ve even caught one on camera in 2019, when we finally took a direct picture of the “event horizon” that marks the point of no escape from a black hole. But why do we care?īlack holes are cast-iron predictions of general relativity, Einstein’s peerless theory of gravity, and yet they stretch it to breaking point. Over the past few years, spectacular observations using gravitational wave detectors and vast telescope arrays have given us pretty good reasons to believe that black holes are lurking out there in the darkness. This makes them impossible to see directly, and so astronomers have had to use a variety of clever techniques to confirm that they actually exist. Eek.Black holes are objects with an intense gravitational pull so strong that not even beams of light, the fastest things in the universe, can escape.

But even Einstein couldn't make black holes go away, and in 1971, astronomers discovered the first clear evidence that Schwarzschild had been right all along. However, it wasn't Einstein himself that made the leap from that theory to the idea of black holes - it was German physicist Karl Schwarzschild, who realized that if a body was heavy enough, the speed another object would have to attain to escape its gravity would be greater than the speed of light.Īccording to Scientific American, though, Einstein himself disliked the idea of black holes, and he even published a paper in 1939 that he clearly hoped would dismantle the idea once and for all. The rubber bends under the weight of the bowling ball, so smaller objects will roll towards the bowling ball, not because the ball itself has some mysterious attractive force but because they're following the dip in the sheet of rubber. According to Einstein's theory, space and matter interact kind of like a flat sheet of rubber with a bowling ball on it.

Center of a blackhole