"Different celestial sources emit their own sorts of gravitational waves, which means that LIGO and its successors could end up hearing something like a cosmic orchestra. 'The binary neutron stars are like the piccolos,' Reitze said. Isolated spinning pulsars, he added, might make a monochromatic 'ding' like a triangle, and black holes would fill in the string section, running from double bass on up, depending on their mass. LIGO, he said, will only ever be able to detect violins and violas; waves from supermassive black holes, like the one at the center of the Milky Way, will have to await future detectors, with different sensitivities."

http://www.newyorker.com/tech/elements/gravitational-waves-exist-heres-how-scientists-finally-found-them