Theory about black holes

[alan2here]

If a light particle went neer a black hole, then it would be pulled towards it, if it was close enough it would be pulled into the black hole. If not it would just be pulled off its otherwise straight path slightly.

 

At some radius light must be able to orbit the black hole, we wouldn't see this light from a distance as it would be going round and round the black hole in the same way as a plant goes round and round a star.

 

If anything large (like a space ship) was pulled into the black hole then it would hit (or float though) this layer of light particles that would seem like a very bright line crossing the ship, possibly damaging the ship due to it's intensity.

 

Of couse this is assuming that light goes at a costant speed, im shure u will prove me wrong on this point.

 

Also check out my other theory thread (about time)

http://www.scienceforums.net/forums/showthread.php?t=22163

[5614]

Sounds reasonable; that there is some projection with which an object could orbit a black hole.

 

Just like a plannet can orbit a star, so a photon could orbit a black hole.

 

However just like there are many different orbital paths around a star, there would be many different orbital paths around a black hole. So you wouldn't suddenly reach a point where there is very intense light, however as you approach the black hole you could come across orbitting photons.

 

Now I'm thinking; what would these photons show you? Well if the photon came from, say, a red dwarf star then you would observer a single red-frequency photon. It would look a bit out of place. You obvserve many distant galaxies and then some red-frequency photon which has been orbitting the black hole for the last 5 light years comes into your eye.

 

Now despite the fact that the human eye is not sensitive enough to detect a single photon if there were many 'old' photons orbitting a black hole then as you approach it you will see lots of random photons from all over the galaxy all at the same time, it would look quite confusing.

[insane_alien]

what you say is pretty accurate. and yeah the orbiting photons would be extremely intense but i think that any ship crossing the event horizon will not be worrying about damage from the light.

[5614]

I suppose there would be a band of orbitting photons.

 

And thinking about it again I suppose it would be very intense, because the number of orbitting photons would be quite high. The number of photons would probably reach some net constant, where the number of photons entering orbit equalled the number being absorbed, but I think it would be quite a high number of photons, so quite/very intense light.

[Klaynos]

 

The energy/radius graph for orbits....

[CPL.Luke]

klaynos could you explain that graph a bit more please?

[5614]

klaynos could you explain that graph a bit more please?

Ye, I second that... what does the graph show?

[Spyman]

The layer of light particles is called a photon sphere.

A photon sphere is a spherical region of space surrounding extremely massive objects such as black holes. At a particular distance, the gravitational force is strong enough that photons approaching along tangents to the sphere will become trapped in an unstable orbit. For black holes, the photon sphere has a radius 1.5 times larger than the Schwarzschild radius (the radius of the event horizon). No orbit with a semi-major axis less than this distance is possible, but within the photon sphere constant acceleration will allow a spacecraft or probe to hover above the event horizon.

[Klaynos]

Oh sorry, for some reason I never checked the thread again. I'm not 100% sure the graph is relevent.

 

But it shows the Energy/Radius, so it shows you the orbital range and shape for differnt energies. So at the bottom of the peak is a circular orbit, anywhere above that is an eliptical orbit up to the x axis above which the orbit makes just a single pass and then flys off into space....

[BigMoosie]

I don't quite understand your graph but perhaps it answers this question.

It seems to me that a ray of light would only be able to orbit the black hole at an exact radius, any less and it would hit, any greater and it would stray (presumably this radius = the event horizon?). So it would be an extremely thin shell of light that orbits the black hole, if the black hole were to change mass in the slightest then all of the trapped light would end up leaving this radius and thus there would never be a great deal of it at any given time.

 

Or perhaps there is a range of radii and this is all wrong.

[nik]

What would the angle haft to be to bend light to the point that it would orbit the object? I know that the sun will bend light about 1.6 degrees and presumably the earth bends light about 1.0552462X10-13 degrees at the same distance.

[[Tycho?]]

What would the angle haft to be to bend light to the point that it would orbit the object? I know that the sun will bend light about 1.6 degrees and presumably the earth bends light about 1.0552462X10-13 degrees at the same distance.

 

Angle isn't a good way to think about it, because it turns more and more as it starts to go into orbit. Not something you can easily express with angles I would think.

[Sisyphus]

I don't quite understand your graph but perhaps it answers this question.

It seems to me that a ray of light would only be able to orbit the black hole at an exact radius, any less and it would hit, any greater and it would stray (presumably this radius = the event horizon?). So it would be an extremely thin shell of light that orbits the black hole, if the black hole were to change mass in the slightest then all of the trapped light would end up leaving this radius and thus there would never be a great deal of it at any given time.

 

Or perhaps there is a range of radii and this is all wrong.

 

I think you're right. Since photons would be travelling at a constant velocity, any orbit would have to be perfectly circular, and it could only have a very specific radius. Anything else would be very unstable, and anything more than a little different would be impossible.

 

EDIT: I wonder... could it be possible for photons to orbit anything besides a black hole? Or would anything massive enough necessarily collapse into one?

[insane_alien]

i suppose a neutron star on the verge of becoming a black hole (or the hypothetical quark star) would have one close to the surface. but they would get absorbed more than around a black hole by matter passing through.

[Daecon]

I would have imagined this orbit to be at exactly the edge of the Event Horizon.

 

Anything inside that orbit, the light will fall into the black hole, anything further out, we will eventually be able to see the light as is flows away from the black hole.

 

At the very edge of the event horizon, the light isn't going anywhere so we will never be able to see it, therefore it will appear at a black region of space - the edge of the Event Horizon.

[Spyman]

Circling the Black Hole at the Photon Sphere

/Snip/ You currently sit at the black hole's photon sphere' date=' where light can travel endlessly in a circle due to the star's great gravitational pull. /Snip/ You are not at the event horizon, which is still below you. /Snip/[/quote'] http://antwrp.gsfc.nasa.gov/htmltest/gifcity/pscirc.html

 

Photon Sphere

/Snip/ For black holes' date=' the photon sphere has a radius 1.5 times larger than the Schwarzschild radius (the radius of the event horizon). /Snip/[/quote']

http://en.wikipedia.org/wiki/Photon_sphere

 

GOOGLE Search on Photon Sphere Black Hole: http://www.google.se/search?sourceid=navclient&hl=sv&ie=UTF-8&rls=GGLD,GGLD:2004-33,GGLD:sv&q=photon+sphere+black+hole

 

EDIT 1:

Note that a "normal" neutron star with a relatively weak external gravitational field does not have a photon sphere. Were it somewhat more compact, it would have a photon sphere, and were it even more compact, it would have an event horizon and be called a black hole.

http://antwrp.gsfc.nasa.gov/htmltest/gifcity/nslens_math.html

 

EDIT 2: Happy Birthday Sisyphus !

[[Tycho?]]

I would have imagined this orbit to be at exactly the edge of the Event Horizon.

 

Anything inside that orbit, the light will fall into the black hole, anything further out, we will eventually be able to see the light as is flows away from the black hole.

 

At the very edge of the event horizon, the light isn't going anywhere so we will never be able to see it, therefore it will appear at a black region of space - the edge of the Event Horizon.

 

As has already been mentioned, the photon sphere is at one and a half times the schwarzchild radius (event horizon).

[psynapse]

;305022'']As has already been mentioned, the photon sphere is at one and a half times the schwarzchild radius (event horizon).

 

How can you have a sphere if the black hole is rotating? The planets orbit in a plane because stars spin. Black holes come from stars, so they rotate.

[J.C.MacSwell]

How can you have a sphere if the black hole is rotating? The planets orbit in a plane because stars spin. Black holes come from stars, so they rotate.

 

It should still collapse to a point.

[Spyman]

Most likely black holes will keep their momentum from rotation before the collapse, but they can still have objects in orbits in different angles than their rotation.

 

The planets orbits in the same plane as the star rotates because they where created from the same rotating cloud of matter.

 

If a rock enters the solar system from outside, with the correct speed and angle, it will be captured by the Suns gravity and orbit with a different angle than the plane.

 

On the outskirts of the solar system there is the Oort cloud which is spherical even though the Sun is rotating. Oort Cloud http://en.wikipedia.org/wiki/Oort_cloud

 

A rotating black hole is a complicated thing, in theory it should have two event horizons and two photon spheres. Kerr Black Hole: http://en.wikipedia.org/wiki/Kerr_black_hole

[DaveC426913]

The planets orbit in a plane because stars spin.

No. Planets orbit in a plane AND stars spin because, as Spyman points out, they both came from the same initial rotating disk of dust and gas. There's one other factor, they are pulled into a plane and kept there because of the combined gravity of the disk. Planets and small bodies out of the plane will be less stable and will eventually get teased into the plane or ejected from the system completely.

 

This will not tend to happen appreciably with black holes for 2 reasons:

1] the light was not part of the initial formation of the system like dust and gas might be

2] the disk of accreting matter around a black hole is not gravitationally strong enough to influence the path of the light into a planar orbit.

[MattC]

It seems to me that a perfectly stable orbit for an orbiting photon would be affected by any increase in mass - something to be expected with black holes. Instead of a very thin sphere, there would just be a photon cloud containing photons heading toward the black hole, photons on orbits that are collapsing but were recently/once in stable orbits, and a (small, I would guess) layer of photons in what is currently the stable orbital distance.