The Origins of Dark Matter

To observe primordial black holes, we would have to observe their gravity affecting objects around them. We can do this with a technique called gravitational micro lensing. The idea here is that you could look at something like a star. And if a black hole happened to lie almost precisely between you and the star, that black hole's gravity will deflect the light from the star around it. But only about one in two million stars would be lensed at any given time.