The most common kind of black hole we know of is a stellar-mass black hole; one with a few to a few dozen times the mass of the sun. There’s no clear upper limit, but astronomers consider any black holes of less than 100 solar masses to be in the stellar-mass black hole category. Current models of galaxy formation indicate that the mass of a galaxy is linked to the mass of its central black hole, too, with bigger galaxies tending to have a bigger central black hole. Encoded in those ripples is the mass of both converging black holes, as well as that of the final, somewhat larger black hole. Current detectors can only sense the mergers of stellar-mass black holes, but future space-based observatories such as LISA (Laser Interferometer Space Antenna) should also be able to “hear” the waves from colliding supermassive black holes.