In Einstein’s theory of relativity, black holes first came about in 1916 when Karl Schwarzschild found a formula which described the spacetime around a spherically symmetric (shaped like a football) and static (doesn’t move at all, completely still) body. Around 10 years later, people realised that this was a black hole! The first “observation” of a black hole was probably the one at the centre of our own galaxy. The first proper direct evidence of a black hole was in 2015 when two black holes smashed into each other and we were able to detect their effect on the spacetime around them (gravitational waves!!!).