Black Hole Suns

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Jason
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Black Hole Suns

Post by Jason » Wed Jan 08, 2014 10:31 pm

Laying in bed the other night I had a random thought: Shouldn't black holes have halos (actually spheres of light, but halos from any one perspective) as light the just grazes the event horizon escapes in a sort of hyperbolic arc? Black holes wouldn't be invisible if this were true, and it seems to me it should be, but would have bright 'rings' or 'halos' of light at the edge of the event horizon.

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Re: Black Hole Suns

Post by mistermack » Wed Jan 08, 2014 11:17 pm

For it to have a visible halo, brighter than the background, the light would need to be focused in some way. There's nothing I can think of that would do that. I would think that any light that escaped would be scattered in completely random fashion.

I do remember reading that when a giant gas cloud falls into a black hole, it gives off an extremely powerful burst of light as it is accelerated to close to the speed of light, and that that has been seen and used to confirm the existence of the black hole.
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Re: Black Hole Suns

Post by JimC » Wed Jan 08, 2014 11:31 pm

The idea of gravitational lensing may be relevant here: http://en.wikipedia.org/wiki/Gravitational_lenses
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Re: Black Hole Suns

Post by PsychoSerenity » Wed Jan 08, 2014 11:54 pm

Actually, what happened about the super massive black hole gas cloud thing this summer? I heard loads beforehand about the scientists excitedly looking forward to it, but nothing about the event or any images.
[Disclaimer - if this is comes across like I think I know what I'm talking about, I want to make it clear that I don't. I'm just trying to get my thoughts down]

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Re: Black Hole Suns

Post by Jason » Thu Jan 09, 2014 12:45 am

JimC wrote:The idea of gravitational lensing may be relevant here: http://en.wikipedia.org/wiki/Gravitational_lenses
That's exactly what I was thinking. I'm only some 80 years late on the theory.

Thanks Jim. :tup:

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Re: Black Hole Suns

Post by pErvinalia » Thu Jan 09, 2014 2:46 am

Your idea makes sense, but where is this light source coming from? I wouldn't think the collection of stars behind a black hole would make enough light to cause a halo.
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Re: Black Hole Suns

Post by pErvinalia » Thu Jan 09, 2014 2:47 am

mistermack wrote: I do remember reading that when a giant gas cloud falls into a black hole, it gives off an extremely powerful burst of light as it is accelerated to close to the speed of light, and that that has been seen and used to confirm the existence of the black hole.
Hawking Radiation.
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Re: Black Hole Suns

Post by JimC » Thu Jan 09, 2014 2:57 am

rEvolutionist wrote:Your idea makes sense, but where is this light source coming from? I wouldn't think the collection of stars behind a black hole would make enough light to cause a halo.
A galaxy directly behind can produce the effect...
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Re: Black Hole Suns

Post by JimC » Thu Jan 09, 2014 3:01 am

rEvolutionist wrote:
mistermack wrote: I do remember reading that when a giant gas cloud falls into a black hole, it gives off an extremely powerful burst of light as it is accelerated to close to the speed of light, and that that has been seen and used to confirm the existence of the black hole.
Hawking Radiation.
No, rEv. Hawking radiation is an odd quantum phenomenon, to do with the production of particle pairs from empty space; when this happens just beyond the event horizon, it has the effect of very slowly decreasing the mass/energy of the black hole. It would be very weak in comparison to gravitational lensing.

http://en.wikipedia.org/wiki/Hawking_radiation
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Re: Black Hole Suns

Post by pErvinalia » Thu Jan 09, 2014 3:08 am

I don't think mm was referring to gravitational lensing. Perhaps he was right, though. I think I've heard accounts of black holes and/or neutron stars etc stripping the gas of nearby stars. I guess when the gas accelerates enough, it probably turns to some sort of plasma and emits a lot of radiation.
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Re: Black Hole Suns

Post by mistermack » Thu Jan 16, 2014 2:13 pm

I don't think that gravitational lensing qualifies for what Făkünamę described in the op.

It's a lens effect, caused by the progressive bending of spacetime, around an extremely massive object, like a galaxy cluster or super super massive black hole, or summat simliar. So it doesn't cause a halo effect around a black hole from any direction, it just produces false images of bright objects that are perfectly in line with the observer and the massive object.

For a black hole to have a halo of light, that just evaded being sucked in, you would need a lot of very bright light sources, very close to it, and they would drown out any halo effect, even if it existed.

Looking backwards at it, if you tracked the light back to the black hole, there would need to be some kind of focussing effect, of most or all of the available light being concentrated to a small area around the black hole, and then released into space to be observed. I don't think there's any mechanism for that.
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Re: Black Hole Suns

Post by Mysturji » Thu Jan 16, 2014 2:33 pm

I think gravitational lensing is EXACTLY what Făkünamę described in the OP.
But there would have to be a fairly bright light source behind the black hole for it to be noticable.
Check out these images of gravitational lensing:
http://apod.nasa.gov/apod/ap130917.html
http://apod.nasa.gov/apod/ap111221.html
http://apod.nasa.gov/apod/ap111017.html
http://apod.nasa.gov/apod/ap100620.html
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Re: Black Hole Suns

Post by Scott1328 » Thu Jan 16, 2014 7:13 pm

Wouldn't the light that approached so close to the even horizon become deeply red shifted?

Gravitational lensing can happen over inter galactic distances and a black hole is not required and certainly wouldn't result in a halo.

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Re: Black Hole Suns

Post by Animavore » Thu Jan 16, 2014 7:18 pm

I've tried all day to resist, but I can't.

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Re: Black Hole Suns

Post by Animavore » Thu Jan 16, 2014 7:19 pm

Lol! Unintentional double entendre.
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