It's easy enough for us to change matter into energy, take a wood log and burn it, but is there any way we know to change energy to matter? What if black holes were doing it? Catching and compacting energy and assembling it into a particle that has no gravity (or maybe has anti-gravity?) so it can float free from the black hole. I know this is highly speculative and it would be an unknown particle, one that we would have trouble detecting.