Also if you throw matter into a black hole just right you can get its equivalent (or half its equivalent I forgot which) out in energy.
Not in useful energy, if you're thinking of using Hawking radiation; it comes out in very high-entropy form. I was so sad when I realized that the "Hawking reactor" I'd invented in fifth grade would violate the Second Law of Thermodynamics.
I wasn't talking about Hawkings radiation. If I throw matter in a black hole just right, I can get half the mass to come out in low-entropy photons. That's why the brightest objects in the universe are black holes that are currently eating something.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.