A team of astrophysicists from Italy and the United Kingdom has calculated that in the observable Universe, a sphere of diameter around 90 billion light-years, there are at least 40*1018 stellar-mass black holes. An artist’s impression of a group of stellar-mass black holes. Image credit: NASA / ESA / Hubble / N. Bartmann. The formation and evolution of black holes in the Universe is one of the major issues to be addressed by the modern research...
