The Gravitational Wave Background of Supermassive Black Hole Mergers

The gravitational wave signals that we look for come from supermassive black holes, which are anywhere between 100 million to a billion times the mass of the sun. And so because our black holes are so much more massive, the signals that we're looking for in fact about a million times stronger than LIGO. So it's not just one signal. It's something like 100,000 potentially a million merging supermassive black hole binaries all at the same time creating this symphony of sound and very low frequencies.