[dd_xplore]

Also to put in perspective, most of the mass isn't converted to energy in either nuclear or hydrogen bombs, it's just the bond energy. Pure energy for a given quantity of matter is released only in case of annihilation-like event(merging with anti matter). So even fusion releases max 0.7% energy of the mass

I'm not sure what happens in black hole merger.. is it an annihilation like event or is just fusion...

[simonh]

The black holes orbit each other, and get closer and closer. This emits gravity waves, and when they merge a large proportion of their combined mass gets emitted as gravity waves. These are what LIGO is detecting.

[arbitrandomuser]

The bond energy is also mass . Energy is mass , If you had a nuclear reactor surrounded by gas and this setup ran a turbine which compressed a humungous spring and this whole setup was completely sealed and sits on a gigantic weighing scale. You run the nuclear reactor, the spring compresses gaining potential energy, waste heat goes into the gas molecules as kinetic energy. As the reactor progresses converting "mass to energy" does the weighing scale become lighter ?

[deepsun]

Well, weighing scale doesn't measure mass, it measures weight. It's just scales' UI converts it to kg/lb for usability, instead of showing N it actually measures (weight is a force, and force is measured in newtons).