I learned that when matter is transformed into energy in a fusion reaction that the gravity associated with the matter that has transformed into energy is not lost. Electromagnetic energy has gravity and is not just a property of mass. I was given this answer on a question about black holes that are very hot (trillions of degrees?) inside, transforming matter into energy passed the event horizon, but not losing any gravity in the process. How does a massless electromagnetic wave generate the property of gravity? Electromagnetic waves are two interacting fields. Light differs in energy based upon wavelength. The shorter the wave length, the higher the energy, and, if I understand, the greater the gravity. If gravity can be simplified to a property of two mutually supporting fields moving through a space then can gravity become a property of how much space a quantity travels through from point to point? A high energy light wave moves straighter through space than lower energy light wave.