None, really. At least, for us, and now. A black hole can be dangerous if it's very massive (such as a supermassive black hole). But mainly, a black hole would be completely harmless, unless it gets close - and the nearest known black hole is at a distance of about 3000 light-years. Even a supermassive black hole would be harmless at such a distance.
There is no evidence that white holes exist.
Hardly any. The nearest known black hole is at a distance of about 3000 light-years; even if one of the nearest stars were actually a black hole, it wouldn't be particularly dangerous.
Not much. The closest (known) black hole is at a distance of about 3000 light-years.
When you get close to a black hole, it will stretch you to where all your insides get crushed.
Anything that falls into a black hole becomes part of that black hole's mass, which makes the gravity stronger and causes the event horizon to grow larger.
Very, even light ain't escape their gravity. A black hole might be the ultimate Doomsday weapon, scientists are attempting to create the phenomena on a smaller scale in the lab. for an interesting story about the subject, see Disney's "The Black Hole"
They vaporize anything in their path. Well, it stretches so much that all of the particles are separated and sucked into the black hole.
That would depend on the mass of the black hole, and how close it came. A black hole the size of a star, a few light-years distance, would not be any more dangerous than a star at the same distance.
The collapses star gets squeezed by collapses gas and turns into a black hole.
A Schwarzschild black hole is a non-rotating black hole. The Kerr black hole is a rotating black hole. Since the latter is more complicated to describe, it was developed much later.A Schwarzschild black hole is a non-rotating black hole. The Kerr black hole is a rotating black hole. Since the latter is more complicated to describe, it was developed much later.A Schwarzschild black hole is a non-rotating black hole. The Kerr black hole is a rotating black hole. Since the latter is more complicated to describe, it was developed much later.A Schwarzschild black hole is a non-rotating black hole. The Kerr black hole is a rotating black hole. Since the latter is more complicated to describe, it was developed much later.
It is dangerous for anybody who gets near it. Please note that the nearest known black hole is at a distance of a few thousand light-years, and the Sagitarius A* supermassive black hole - the one at the center of our galaxy - is at a distance of about 26,000 light-years, so they pose no immediate danger. basically no one knows and yes it is quite dangerous, no one so far reached it as does take a distance of 26,000 light years, scientists are trying to design a new type of rocket which can travel very fast.