The researchers of Japan shows that dark matter is not made up of tiny black holes

Researchers led by Kavli Institute for the Physics and Mathematics of the Universe in Japan has put a theory speculated by the late Stephen Hawking to its most rigorous test to date, and their results have ruled out the possibility that primordial black holes smaller than a tenth of a millimeter make up most of dark matter. They used the gravitational lensing effect to look for primordial black holes between Earth and the Andromeda galaxy. However, gravitational lensing effects are very rare events because it requires a star in the Andromeda galaxy, a primordial black hole acting as the gravitational lens, and an observer on Earth to be exactly in line with one another. In order to maximise the chances of capturing an event, the researchers used the Hyper Suprime-Cam digital camera on the Subaru telescope in Hawaii, which can capture the whole image of the Andromeda galaxy in one shot. Taking into account how fast primordial black holes are expected to move in interstellar space, the team took multiple images to be able to catch the flicker of a star as it brightens for a period of a few minutes to hours due to gravitational lensing. The team’s results showed primordial black holes can contribute no more than 0.1% of all dark matter mass. Therefore, it is unlikely the theory is true.