How many black holes are out there in the Universe? A new study has investigated the demographics of stellar mass black holes, which are black holes with masses between a few to some hundred solar masses, that originated at the end of the life of massive stars. According to the new piece of research, a remarkable amount around 1% of the overall ordinary matter of the Universe is locked up in stellar mass black holes. Astonishingly, the researchers have found that the number of black holes within the observable Universe (a sphere of diameter around 90 billions light years) at present time is about 40 trillions, 40 billion billions (i.e., about 40 x 1018, i.e. 4 followed by 19 zeros!).