Black Hole

This video is about how efficient various reactions are at converting mass to energy, as we know from the Einstein mass-energy equivalence of E=mc^2.

Antimatter is very efficient but it is not naturally-occurring. Chemical reactions like fire or explosions are very inefficient. Nuclear fission and nuclear fusion are better, but not amazing on an absolute scale. Non-rotating black holes (Schwarzschild) and rotating (Kerr) are by far the most efficient, due to their accretion disks and very small radius of their innermost stable circular orbits.

The unreasonable Efficiency of Black Holes