Originally posted by Grunt
Getting close is not a problem. Getting out is what I would be anxious about.
Concernig radiation, a BH is a safe place cos' it emits nothing.
Neutron star: Isn't it the thing which turns into a BH ?
I suppose the effect is similar. Enormous gravity which sucks in material from close stars.
Okay we have a case here where an example would prove useful.
Suppose tomorrow the sun magically (and it would have to be magically since it couldn`t occur naturally) turned into a black hole. What would happen to Earth.
The answer is surprisingly little. The Earth wouldn`t go spinning off it's axis and flying towards the sun like most people think it would. In fact the Earth would continue in its normal orbit with no new effect whatsoever from the black hole. (of course life would be wiped out due to the lack of a star etc)
The reason for this is that gravity is a function of mass. A black hole in the same place as the sun with the same mass as the sun would have exactly the same effect on the Earth as the sun.
So since a black hole has no more mass than the star that created it (in fact it has less since it loses mass during the supernova) it can`t really affect objects far away any more strongly than the star it was created from did.
However once you get within the radius of the original star then you get problems. 5000 miles into the sun the gravitational pull is actually less than on its surface. This is because the gravity inside a sphere actually gets less and less as you approach the centre (since some of the gravity from the mass below you is cancelled out by the gravity of the mass above you).
In a black hole you don`t get this effect. The gravity just keeps on increasing until you reach the singularity. That's what makes a black hole so dangerous. The closer you get to it the more strongly it pulls you, but as I said this effect only makes a black hole dangerous once you`re within the radius of a star of equal mass.
As for radiation black holes do in fact emit large amounts of gamma and x-rays whenever they eat something. (can't remember if they only emit from the poles or just mainly at the poles though).