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Black Holes visual appearance


Earl
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The classical picture shown of a black hole is not dissimilar to water going down a plug hole.

How does the angle of the observer effect this view though? what if you were behind the black hole or to the side of it? or does it look the same from any angle?

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As i understand it the actual black hole would be a sphere, so i assume it would be somewhat similar to those 'early solar system' animations you see with the clouds of matter/dust orbiting the star, except the star is black and instead of orbiting it's spiraling inwards - apart from when the matter comes in from a different angle, of course.

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Black holes are singularities where the laws of physics break down. Out to the event horizon though, their gravity is such that light cannot escape and so look black. I think they do emit some radiation - Hawking Radiation - but I know little about it.

The picture of water going down the plug hole is just an analogy. It is probably a reasonable representation of the potential of the black hole as you get further away from it. A force is just how steep this potential is, so as you get closer the force pulling you in is higher, reaching infinity at the singularity.

I believe a black hole would be spherically symmetric and therefore look the same from from all directions. Rotation produces deviations from spheres, such as the discs that form when black holes accrete matter, but they are not part of the black hole itself.

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I think the key question as to what it looks like is whether or not the black hole is spinning. If it is spinning (eg formed from the collapse of a spinning star) it will produce jets and an accretion disk of luminous material being dragged into the black hole. see for example Direct observation of black hole accretion disc . I don't know whether you get an accretion disk with a non-rotating black hole (in fact I am not sure whether a non-rotating black hole is feasible).

old_eyes

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If blackholes have such a strong gravitational pull that not even light can escape then how come those stars (in that link) are able to swing so close to it and then back out again? Shouldn't they all be getting sucked in?:)

I've asked lots of daft questions lately so I might as well carry on now.:)

Edited by scogyrd
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Well my question comes from the "Typical illustration" but that does not satisfy me at all as there always 2 dimensional and never have a look around the back to see whats going on...

Now if it was said that like a rainbow it is visible purely from the observers perspective, but all observers can see it. then it could like the typical view from any angle... maybe?

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If blackholes have such a strong gravitational pull that not even light can escape then how come those stars (in that link) are able to swing so close to it and then back out again? Shouldn't they all be getting sucked in?:)

I've asked lots of daft questions lately so I might as well carry on now.:)

There is a boundary around the singularity beyond which anything, including light, effectively vanishes forever (I think it still called the Event Horizon, but my terminology might be off). This boundary depends on the mass of the black hole. More massive black hole, bigger event horizon. The stars are being affected by the gravity - you can see they are attracted to the place where the black hole is inferred to be. But they are moving fast enough and don't go close enough to get fatally captured.

old_eyes

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Well my question comes from the "Typical illustration" but that does not satisfy me at all as there always 2 dimensional and never have a look around the back to see whats going on...

Now if it was said that like a rainbow it is visible purely from the observers perspective, but all observers can see it. then it could like the typical view from any angle... maybe?

If the black hole is spinning then it is axially symmetric, so the emission from the accretion disk will look the same form whichever side you are looking. if you are looking in the place of the disk It is possible to detect which side of the accretion disk is spinning away from you and which side is moving towards the observer by doppler shift in the emissions. Obviously if you are looking directly down onto the disk there is emission but no doppler shift. As you change the angle between straight down and side on you get a mixture of the two views in proportion to the angle.

If the accretrion disk is being fed by material from a star in orbit around the black hole (the usual graphic of a black hole 'eating' a star), then the accretion disk is no longer symmetric.

old_eyes

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As a black hole is said to be a tear in the fabric of space time, so in effect it would look the same from all angles, and visible though it's interaction with other celestial bodies or elementary matter/particles, according to quantum mechanic's energy wave's in space create tiny particles, one with positive energy and the other with negative, these pair of particles appear and then collide and destroy each other, Hawking proposed that if these two particles came into being near the event Horizon of a black hole, the negative particles would fall in, however the positive particles would just have enough energy to escape and was given the name Hawking radiation.

Edited by Si W
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My understanding is that you would not see the black hole at all as it will be completely surrounded by the mayer falling into it. One of the ways we identify the location of black holes is to look for powerful x-ray sources; the x-rays being emitted by the matter falling in as it is ripped apart by the immense tidal forces. How would this look? I think the previous comment about 'classical' images of proto-planetary disks around young stars is probably not far off, the scale depending on the mass of the black hole. I guess there are likely to be strong polar jets, too, but don't know enough to make an educated guess, to be honest. Where the mass has run out and you can 'see' the event horizon, who knows? Maybe just a dark space moving across the background field of stars?

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