Black holes are the most mysterious objects in the universe. They’re places where physics is pushed to its most extreme, where light cannot escape and where space-time itself is twisted and even punctured, leading to the most incredible and counter-intuitive phenomena. A black hole is a region of space where gravity is so strong that nothing, not even light, can escape from its grasp. Within a certain proximity of one, closer than the black hole’s ‘event horizon’, you’d have to travel faster than light to get away from it. Since nothing can go faster than light – at least as far as scientists know – then whatever falls down a black hole stays down the black hole.
The discovery of black holes dates back to Einstein’s general theory of relativity. Einstein himself didn’t predict the existence of black holes per se, but general relativity, which describes mass, space, time and gravity, provides the mathematical foundations for understanding them. These were realised by Einstein’s German compatriot Karl Schwarzschild, who solved Einstein’s equations to describe the gravitational field around a nonrotating, spherical mass and to determine the Schwarzschild radius, which is the size of a black hole’s event horizon. In the 1960s, Roy Kerr solved Einstein’s equations for a more realistic scenario – that of a black hole that’s spinning.
We’ve already mentioned that light cannot escape a black hole, and the event horizon is its ultimate boundary of no return. Once something has crossed the event horizon’s invisible boundary, it can never return from the black hole. Let’s picture what is going on using an oft-mentioned analogy, that of a rubber sheet, which we have to imagine as being the fabric of space for this analogy to work. If you want to try this at home, a bedsheet held tight at each corner should suffice. a little. In general relativity, that dip in the fabric of space is called a gravitational well – it represents Earth’s gravitational field. Now put a tennis ball on the sheet, imagining that it’s the Sun. You’ll notice that it creates a bigger dip than the ‘Earth’, not necessarily because it’s larger, but because it has more mass. If you were to zip ball bearings past both the marble and the tennis ball,
