Wandering Black Holes: Do they pose a danger?

[Manuel I Komnenos]

1) What do we know about them?
Have scientists actually witnessed wandering black holes or is their existence based on speculation just like the wormholes? My guess is that if they were generally million times smaller than the black holes in the centers of the galaxies it would be difficult for astronomers to witness or calculate any changes in solar systems far away.

2) However, if they do exist, how common are they?

3) What kind of damage would a wandering black hole inflict if it passed through our solar system? Would it alter the movement of any planets, say Venus, causing it to wreck havoc in the solar system and collide with other planets? I guess this depends on its size and how close it would pass to the planets.

4) What kind of damage would it inflict if it passed close to Earth? Depending on size, would this result in relatively small damage such as loss of an amount of Earth's atmosphere and high volcanic activity and tsunamis, or would the Earth simply get eaten by the black hole?

5) When would we get notified of it? Would there be any way to stop this doomsday event?

[Randarkmaan]

Well, considering how very small they would be, this means that it's mass is much smaller, and so is it's gravitational attraction, not to mention the event horiszon. One would have to be very close for it to be very dangerous at all. It's not like something so small just wandering about has any real chance of actually hitting everything.

Black Holes are basically what you get if you if you just compress a mass together so dense that you can get a region of space where the gravitational field is so strong that the escape velocity is greater than the speed of light. However depending on the mass that is compressed the radius in which the field is this strong varies. So when you have teensy tiny black holes, you have to get very close for it to be like that. Though if you're not a photon, then the event horizon is the farthest you can go, though I guess that if the black hole is really small, then this is not as impressive either. In fact I believe some thirty or fourty years ago, maybe more, there were many scientists who thought there were miniscule black holes everywhere, such as electrons actually being this.

Also what what many fail to take into account is that the normal gravitational effects as felt across astronomical distances will not be that cataclysmic at all really for 'normal' black holes resulting from supernovae, where black holes may form if the remaning mass (most of it having been blown away) is above like 2-2,5 solar masses. So the actual gravitational pull from such a black hole over normal (that is astronomical) distances should not be greater than for stars with masses 2 or 3 times that of the Sun. Though ofcourse such an object intruding into the solar system would be rather disastrous. But this does not seem to happen all too often, and if it does we will probably be warned (in wain ofcourse).

As for very, very small black holes that are undetectable even at relatively short distances... you should not really worry about them. Granted we can hardly detect the big ones, but we can see detect their gravitational impact in for instance binary systems, and since the gravitational force gets exponentially larger as the distance becomes smaller... well you see where I'm going.


Noticed I didn't answer too many of the questions. But I read an article in Science how there don't really seem to be any wandering black holes, though here they were thinking of the really big monsters in galactic cores and such.

[Gordon Freynman]

1) What do we know about them?
Have scientists actually witnessed wandering black holes or is their existence based on speculation just like the wormholes? My guess is that if they were generally million times smaller than the black holes in the centers of the galaxies it would be difficult for astronomers to witness or calculate any changes in solar systems far away.

2) However, if they do exist, how common are they?

3) What kind of damage would a wandering black hole inflict if it passed through our solar system? Would it alter the movement of any planets, say Venus, causing it to wreck havoc in the solar system and collide with other planets? I guess this depends on its size and how close it would pass to the planets.

4) What kind of damage would it inflict if it passed close to Earth? Depending on size, would this result in relatively small damage such as loss of an amount of Earth's atmosphere and high volcanic activity and tsunamis, or would the Earth simply get eaten by the black hole?

5) When would we get notified of it? Would there be any way to stop this doomsday event?

1) I don't believe there have been any wandering black holes witnessed, but they are predicted to exist.

2) No one knows.

3) Depending on the size and how close it got, the effects could be anywhere from disrupting the orbits of the outer planets to completely erasing all traces of our solar system from the face of the universe.

4) If a black hole of any reasonable size got close enough to us, say with in the distance of the sun, in all likelihood we would get sucked into it eventually.

5) We'd certainly know of it for at least a few days or weeks in advance, possibly months or years if astronomers got "lucky". It wouldn't matter however, there would be nothing we could do to stop it.