The NASA Chandra Space Telescope has just revealed the smallest black hole ever detected, just 2.7 times the mass of the Sun. It would be the result of the fusion of two neutron stars at the origin of the gravitational wave detected in August 2017.
GW170817 is the code name of the gravitational wave detected by the two antennas of the American LIGO detector on August 17, 2017. At the time, the cosmic wave had aroused great excitement among astrophysicists: the recordings showed that it was the result of the merger of two neutron stars, these dense hearts of big stars at the end of their life having already exploded. But GW170817 still hid a nice surprise that the Chandra space-sensitive X-ray telescope has just revealed: during this merger, the smallest black hole ever detected had formed, which barely collects 2.7 times the mass of the Sun.
If these deductions are confirmed, the researchers now hold the recipe for making featherweight black holes. Here it is: take two big stars at the end of life, wait for them to explode in a supernova, knowing that when a star explodes, its dense heart forms a neutron star. With great luck, the two would be close enough to enter the gravitational field of each other. Then wait for their orbit to get closer to the point where the two stars collide and emit a gravitational wave forming a tiny black hole.
We already know about supermassive black holes, at least several million solar masses, that are at the heart of galaxies and also the stellar black holes, which accumulate a few tens of solar masses, but this is a new category of black holes that was formed during the issue of GW170817.