Post-Newtonian (PN) theory
Not explicitly mentioned in the crianca summary, but the general topic of supermassive black holes and gravitational waves is discussed. However, a related analogy can be found for the concept of "gravitational waves from single galaxy couples," which suggests a focus on understanding complex physical phenomena.
Technical definition
An extension of Newtonian gravity that accurately predicts gravitational wave emission in strong-field, relativistic situations.