BBC Science Focus Magazine Advertisement In the very beginning, the Universe was incredibly hot and dense – so much so that a random local fluctuation that increased the density of an area by only 50 per cent would be enough to spark gravitational collapse into a black hole. Unlike the black holes we see in our modern Universe, the hypothetical ‘primordial’ black holes created at this time didn’t form from a collapsing star, which means they could have a wide range of masses, including very small ones. Since they can be tiny and give out no light, primordial black holes are a potential candidate for dark matter, the mysterious material that makes up about 85 per cent of all matter in the Universe and can’t be seen through telescopes.