The quick answer would be to say they have an immense gravitational pull, and if you get close enough, past the event horizin, there is no way to escape or survive. They are extremely long lived, they are almost invisible unless they are absorbing an object and, surprisingly, they can be quite fast.
The more indepth answer would be that danger is a subjective term. Black holes certainly can be dangerous, but to us here on earth black holes dont present an immediate threat. The nearest one is 1600 light years away, far too far to exert any gravitational pull. Equally, scientist arent worried about a black hole being formed anywhere close anytime soon. And few scientists are worried about creating artificial black holes; not only would they radiate away far too quickly but ,even if they were stable, they would be too small and lite to 'suck' anything in.
But, having said all that, there is one final way a black hole could be dangerous. Black holes are one of the leading suspects in the creation of 'gamma ray bursts', massive explosions that dwarf even supernovas. If one happened in our galaxy, and was pointed as us, there is a small possibility it could cause an extinction event by messing with the ozone. Several mass-extinction events millions of years ago could possibly have been caused by such a blast.
Luckily there is only 1 of these bursts per 100000 or 1000000 years in our galaxy, and only a few percent of those would be angled at earth. So black holes, whilst certainly dangerous, pose little threat to humans here on earth.
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.
A black hole is more dangerous than a dark hole. Black holes are regions in space with gravitational forces so strong that not even light can escape, while a dark hole does not have a specific scientific definition and may refer to areas of space with lower light or energy levels.
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.
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
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.
A black hole is more dangerous than a dark hole. Black holes are regions in space with gravitational forces so strong that not even light can escape, while a dark hole does not have a specific scientific definition and may refer to areas of space with lower light or energy levels.
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.
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.
White holes are theoretical objects that are the opposite of black holes, expelling matter instead of absorbing it. They are not considered to be dangerous like black holes, as they do not have the same gravitational pull or ability to trap objects with their intense gravitational force. White holes are not thought to exist in our universe.