It would be consistent with the debris/gas ring neither edge-on nor en-face to us. That way light from the far portion of the disk ( which would normally be occulted by an 'ordinary' body ) is bent around to come to our viewpoint. That adds to the light seen directly from the nearside disc and so in total that is why the disk looks brighter on one side. The event horizon ( classical description ) is that surface where light will circulate ( forever ) around the central mass. Light further out may circulate a finite number of times before escaping.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Thanks for that explanation Mike! I was wondering about the shape and varying intensity of the disk. But why is it a ring and not an orbiting sphere of debris, gas and photons? What imparts an axis to the spin?
Ideas are not fixed, nor should they be; we live in model-dependent reality.
Thanks for that explanation Mike! I was wondering about the shape and varying intensity of the disk. But why is it a ring and not an orbiting sphere of debris, gas and photons? What imparts an axis to the spin?
The rotation of the black hole itself. Its gravity field as it rotates imparts a force on any particle that is not in the same plane, such that the orbit matches the plane of the hole's rotation. By the time the particle has worked its way down to the event horizon the accretion disk is likely as thin as a sheet of paper. Remember it will have made millions of trips around the hole by then.
Thanks for that explanation Mike! I was wondering about the shape and varying intensity of the disk. But why is it a ring and not an orbiting sphere of debris, gas and photons? What imparts an axis to the spin?
There's no physical law that prevents it from being an orbiting sphere of whatever. The fact that it is a ring reveals something of the origin of the system. This would be also true if it were the rings of Saturn or the pancake like shape of the Milky Way. Prior to the formation of the hole there would have been all manner of material ( entire stars etc ) orbiting the centre of mass of the system. With respect to that central point each object has an angular momentum vector. These vectors from all objects can be summed. It is just unlikely that they would all happen to sum to zero ie. no nett angular momentum about the centre of mass. Hence there must be a non-zero nett angular momentum which will point in some direction. That direction will define the axis of the disc that later forms, because angular momentum is conserved - even if a black hole forms. As the system evolves towards a planar disc interactions b/w orbiting objects takes place with the effect of reducing velocity components which are parallel to the nett angular momentum axis. There's a theorem or two about this, basically asserting that the out of plane velocity components are nulled out, eventually leaving a rotating disc.
Furthermore as material spirals inwards towards & into the central hole then they must lose linear momentum to do this. There must be some mechanism(s) that transfer linear and thus angular momentum to material further outwards. With time therefore one tends to have a zone/gap deep in near the hole which is pretty much clear of material, meaning material doesn't spend much time there before it crosses the horizon. Also interactions b/w adjacent material in the disc - a sort of friction really - generates the radiation that enables us to view the disc at all. It's a fascinating topic.
Cheers, Mike.
( edit ) I forgot to say : finding this image of an event horizon is yet another huge win for General Relativity and Albert Einstein's genius ! :-))
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
https://xkcd.com/2135/
)
https://xkcd.com/2135/
Richard
What a tremendous picture
)
What a tremendous picture !
It would be consistent with the debris/gas ring neither edge-on nor en-face to us. That way light from the far portion of the disk ( which would normally be occulted by an 'ordinary' body ) is bent around to come to our viewpoint. That adds to the light seen directly from the nearside disc and so in total that is why the disk looks brighter on one side. The event horizon ( classical description ) is that surface where light will circulate ( forever ) around the central mass. Light further out may circulate a finite number of times before escaping.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Thanks for that explanation
)
Thanks for that explanation Mike! I was wondering about the shape and varying intensity of the disk. But why is it a ring and not an orbiting sphere of debris, gas and photons? What imparts an axis to the spin?
Ideas are not fixed, nor should they be; we live in model-dependent reality.
cecht wrote:Thanks for that
)
The rotation of the black hole itself. Its gravity field as it rotates imparts a force on any particle that is not in the same plane, such that the orbit matches the plane of the hole's rotation. By the time the particle has worked its way down to the event horizon the accretion disk is likely as thin as a sheet of paper. Remember it will have made millions of trips around the hole by then.
cecht wrote:Thanks for that
)
There's no physical law that prevents it from being an orbiting sphere of whatever. The fact that it is a ring reveals something of the origin of the system. This would be also true if it were the rings of Saturn or the pancake like shape of the Milky Way. Prior to the formation of the hole there would have been all manner of material ( entire stars etc ) orbiting the centre of mass of the system. With respect to that central point each object has an angular momentum vector. These vectors from all objects can be summed. It is just unlikely that they would all happen to sum to zero ie. no nett angular momentum about the centre of mass. Hence there must be a non-zero nett angular momentum which will point in some direction. That direction will define the axis of the disc that later forms, because angular momentum is conserved - even if a black hole forms. As the system evolves towards a planar disc interactions b/w orbiting objects takes place with the effect of reducing velocity components which are parallel to the nett angular momentum axis. There's a theorem or two about this, basically asserting that the out of plane velocity components are nulled out, eventually leaving a rotating disc.
Furthermore as material spirals inwards towards & into the central hole then they must lose linear momentum to do this. There must be some mechanism(s) that transfer linear and thus angular momentum to material further outwards. With time therefore one tends to have a zone/gap deep in near the hole which is pretty much clear of material, meaning material doesn't spend much time there before it crosses the horizon. Also interactions b/w adjacent material in the disc - a sort of friction really - generates the radiation that enables us to view the disc at all. It's a fascinating topic.
Cheers, Mike.
( edit ) I forgot to say : finding this image of an event horizon is yet another huge win for General Relativity and Albert Einstein's genius ! :-))
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal