There’s basically no way to answer these questions using real physics I’m afraid.
It definitely can’t close it’s mouth faster than the speed of light. Yes it would have a strong gravitational pull, almost definitely so strong that it would just collapse into a black hole and not be able to exist. If it weren’t that dense, then it would basically just be a big diffuse gas cloud that couldn’t do much anyway, it would basically have to be a proto galaxy to not collapse into one.
If it’s using magic to exist, then anything is on the table.
If you’re looking for books, then it depends on what field you want to study. Generally just I’d search for recommended textbooks for that field and then I’d definitely buy it and wouldn’t just download it from libgen.is