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. 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.

Black hole definition