Gravitational waves are energy carried in a form called Energy over “Reference Frame!” When two ultra-massive interstellar objects orbit each other, they lose some of their orbital energy over time, which is called ‘Orbital Decay’.
The energy lost during this orbital decay is converted into another form. That form is Gravitational Waves or Gravitational Radiation.
When decayed and ultra-massive objects collide with each other, they generate gravitational waves that carry large amounts of energy, such as gravitational waves captured by Ligo observatory in 2015 and the enistein’s theory together … about 3, + twice as many solar masses. Converting to Gravitational Radiation in some cases.