1)yeah. It's why they talk about solar masses. It's also important to think about energy density. There's a thing hypothesized called a kugleblitz black hole that is formed out of energy or radiation, not matter. If a substance interacts with spacetime then in theory there is some concentration at which that substance can achieve sufficient density to warp spacetime the way we see matter warp it with black hol es.
2) you sure would think so. Their radius depends on the density of energy inside that radius. As that increases so would the radius. It brings up a few big picture problems that hawking, susskind, and many others spent a time formulating rigid answers to. Weird things like virtual particle pairs forming at the horizon and a black hole being some sort of reality generator in a sense, how they radiate energy, holographic firewalls to satisfy the information paradox of their blackness.
3) the black hole is the radius. What's inside, whatever it is, doesn't exist for us. It could be full of cotton candy and unicorns. Relativity doesn't even break, as such. You're not just approaching infinity, you're at infinity, so the questions become meaningless. unless you get more clever about formulating questions. It's not a theoretical boundary, it's a very real boundary. It's like division by zero. X/0 is possible, that's not why we don't do it. We don't do /0 because any number will solve it. It's indeterminite. What's the point of view of a photon? It doesn't have one, because it doesn't experience time. There are bad questions.
4) that radius denotes an area of change. Black holes shouldn't grow quickly, even if we naively assume they don't radiate. Think about the ratio. You're considering density, which is mass over volume. Mass has to grow faster than volume, volume is a cube. unless you're feeding a black hole to another black hole -- but that's supposed to explode mostly. Mass is kind of tricky, really. We're using it to mean "stuffness", but that's a big more vague than physicists prefer. ius good enough for me though. But yes, outside einstein. Inside we can't know. We can guess and susskind thinks that in principle we can find out if we need to (I don't mean humans, I mean the universe) Einstein was intentionally describing the outside, so we have no business considering that a failure. He published two papers later in his career about the inside which is where the idea of wormholes come from. Information can't pass through Einstein's wormholes though.
5) youd have to assume it's the same relationship as between dark matter and normal old matter. Dark matter reacts gravitationally, weakly. Can dark matter pass into and out of the event horizon? Well, if it can and you can prove it can, you've just proven that Einstein missed something. Since gravity indicates a curvature in spacetime, and the event horizon is the location at which spacetime folds back on itself (all degrees of freedom lead to the same point) if there is matter (stuffness) which can sidestep that -- you've proven a new aspect of reality. at least a degree of freedom uninhibited by spacetime, which seems like the same thing. A new dimension. I'm going to guess dark matter that crosses the horizon stays crossed. If there's stuff that doesn't we probably cannot empiracilly confirm it's existence.
arstechnica.com
