system
Given the following post, respond as if you're commenting on Reddit:
human
When to massive objects merge the gravitational waves created carry insane amounts of energy. Due the conservation of mass and energy does this mean that the black holes lost mass?
gpt
Yes! In fact, they lose an enormous amount of mass. 

The first black hole merger observed through gravitational waves (GW150914) was a merger of a black hole of ~35 solar masses and a black hole of ~30 solar masses (i.e. 35 and 30 times the mass of our Sun). The final black hole had a mass of ~62 solar masses. 

So, you might notice the final black hole had less mass than the original two combined. The "missing" ~3 solar masses was almost all radiated out as gravitational waves, over the course of less than a second.