At what distance is black hole noticible?

Question

If a black hole (mass = M(Sun)) approaches us,
how close it could get before astronomers notice?

I am not sure about velocity, but say it has typical
velocity of nearest local stars.

Answer 1

A black hole is typically "noticed" by x-ray emission from a surrounding disc of matter that is spiraling into it (the "accretion disc"). The closest black holes to Earth of about the mass of the Sun are several thousand light years away. As you get much closer than that, the x-ray emission becomes very very noticeable to space astronomy satellites.

Answer 2

I don't know the exactly answer, but according to what I've read about black holes I know that astronomers are able to detect them by the way in which close starts modified their orbits and speed. A few years ago I saw in Discovery Channel that if a black hole approach us, it's magnetic field would affect the Kuiper's belt and the great Oort cloud and thousands of that objects would fall to the Sun, and many of them would crash the Earth and other planets. And they said that even when the black hole be at that distance, the Earth would have catastrophic earthquakes and volcano eruptions caused by the strenght of the black hole magnetic field.

Answer 3

The first poster is correct; If a black hole forms with nothing nearby (nothing to suck in), then it could sneak up very close to us before we would notice. It's only when it's in the vicinity of something (another star, a gas or matter cloud), with objects falling, do we actually "see" the black hole.... usually. The other time we'd be able to see it OUTSIDE the presence of matter would be if it causes gravitational lensing - bending the light we see coming from objects further away. But... we'd have to notice it.

Answer 4

Black holes are normally in the center of the Galaxy and furnish the gravity that holds everything around it for 10 t0 100 light years.

Answer 5

It depends on what is around the black hole. You can't see a black hole. They are the absence of everything, including light. You can only indirectly observe a black hole by overserving the material that is being sucked into it. In that case, scientists have supposedly indirecty observed the supermassive black hole at the center of our galaxy so as to the question, quite a long ways away. Iminient danger from a black hole swallowing our solar system is nonexistent.

Answer 6

A black hole if it could exist would make itself known by it's gravity.
If you couldn't see the moon the tides on earth would act the same.
No evidence exists that there are black holes .
Right now they are theoretical entities,but there are many characteristics about them that make them nonviable entities.