[imatfaal]

That's interesting!  Does everyone agree? 
I always understood that nothing could cross the event horizon from inside to outside.
If space time is so highly curved at the event horizon that not even light can escape how can charge escape be felt outside?
If the charge is felt outside of the event horizon could this not in some sense radiate away energy/mass?
It's also telling you something (information) about the inside of the black hole, isn't this also forbidden?

I understand that 'charge' is conserved in a black hole but does that imply that charge is felt outside the event horizon?  (see last paragraph above)

Gravity is felt o/s the EH - this gives us a measure of mass of the black hole ie information about it.  I do not think we can assume that charge would not also be felt.

[MikeS (OP)]

imatfaal

Can I extrapolate from the above that you think charge would be felt?

Granted gravity is felt outside the EH, that's why space-time is so extremely curved at the event horizon of a black hole that not even light can escape.
Charge would have to propagate faster than the speed of light to stand any chance of escaping.
The EH effectively acts as a shield.
You can think of charge as being similar to the lines of force surrounding a magnet.  These 'lines of force' within the event horizon are so curved they cannot penetrate the EH.
I really don't see any mechanism whereby charge can penetrate (from inside to out) the event horizon.

I would be very interested to hear by what mechanism you think that charge could be felt outside the event horizon?

[Soul Surfer]

As I understand it all the fields propagate through all space and the electric and magnetic fields are no exception to this the effect is that the event horizons for a charged black hole could well be in different places for positively charged negatively charged and neutral particles.

[JP]

I did a bit of searching around the web to find a decent answer to that, Soul Surfer.  It seems there are two effects that allow the field of a charged black hole to interact with matter outside of itself.

The first is that, using only classical results, in-falling matter gives off a field.  Since any external observer would see matter take infinitely long to fall in, I suspect you would get a field from that falling electron forever(?)  But the field would get weaker and weaker and isn't the full answer.

Invoking quantum mechanics, the electrostatic force is mediated by virtual photons.  Virtual particles can cross the event horizon (e.g. Hawking radiation), so a charged black hole can in fact interact via electromagnetism with other stuff. 

All the explanations I found were a bit hand-wavy and I don't really have the time to pick up a book on GR and try to figure it out in more detail, but it seems plausible...

[Geezer]

There's an easy enough way to find out. All you have to do is bombard a BH with charged particles for a bit then see if the field strength in its vicinity (outside the event horizon) has intensified.

Seems simple enough......

[CliffordK]

There's an easy enough way to find out. All you have to do is bombard a BH with charged particles for a bit then see if the field strength in its vicinity (outside the event horizon) has intensified.

Seems simple enough......

Now, why didn't I think of that.
I'll make a quick jaunt over to the nearest black hole, 1,600 light years away.

Just after I figure out how to harvest and transport every electron in our sun to see if it will give it black hole indigestion.

[MikeS (OP)]

If a black hole had charge and it rotated (which it almost certainly would) then presumably it would have a magnetic field.  If the charge can be felt external to the EH then I can see no reason why the magnetic field would not be felt external to the EH.

Is this the case? I don't believe it is.