I have been wondering something. Assuming strange quark stars exist (and I know that this is still too early to call), is it possible that a black hole might just be an overgrown quark star that has gone over the required mass (say from feeding on a nearby star or a collision)? Is there any evidence that a black hole really has no surface, as I have read people say, or is it just assumed because there is no way to detect one? Finally, is there any evidence for a form of matter even more dense than a quark (and therefore something that black holes might be made of)? Thanks in advance - I know these might seem to be silly questions, but its something I have been wondering about.