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I find it strange that no one has characterized that boundary layer where light orbits the black hole. We know that massive objects distort space and as a resul

by bawana 8y ago

I find it strange that no one has characterized that boundary layer where light orbits the black hole. We know that massive objects distort space and as a result alter the path of light. At sufficiently close distances, space is so distorted that 'not even light can escape'. Everyone assumes that light 'falls into' a black hole. But for light to do that, it would need a velocity greater than light itself if it is in orbit around the black hole. Thus, any light that is captured by tangential approach to the black hole and goes into orbit around the black hole, has to stay in orbit. Any acceleration that is needed to change the path of light would add to the velocity of light and that should not be possible. Over time, the only light that is not absorbed by virtue of collision with the singularity at the center of the black hole is the light in orbit around it. This is distinct and different from the light resulting from nuclear fusion of material in the accretion disc which is just outside.

l33tman 8y ago
The perfect orbit geodesic is infinitely thin and therefore unstable due to quantum mechanics. So even if a photon is injected at the perfect orbit it would not stay there, it would fall in or eject. Besides, even without invoking QM, any other matter that actually falls into the hole afterwards would inflate the event horizon, causing those photons caught in the perfect orbit to now exist just infinitesimally within the orbit and fall in.
- soVeryTired 8y ago
  Do you need quantum mechanics to see that a photon would fall in or eject? Presumably a little movement from the black hole would do the trick too.
  - Pharmakon 8y ago
    Right, but the QM view tells us that even a perfectly stationary chargeless black hole in a perfect vacuum alone in a perfectly smooth universe would still experience fluctuations in its event horizon. Unlike the Classical view, QM reveals that even in principle there exists a degree of instability in the horizon.
AlanSE 8y ago
Light that comes within 3/2 of the Schwarzschild radius (Rs hereafter) gets captured by the black hole. Of course I don't mean that it beelines in a direct radial direction to the singularity. Of course it takes a curved path depending on its exact trajectory, but at some point on this trajectory it hits the event horizon. Nothing that hits the event horizon can ever come back out again (according to an observer at sufficient distance). This magic 3/2 Rs radius is the Innermost Bound Circular Orbit (IBCO), and is the truthfully correct scientific principle that you are grasping for. It is not a stable orbit, but it is an orbit. In a theoretical world, if a photon had the perfect trajectory to enter this orbit, it could orbit there indefinitely, but it is unstable, so in the real world it doesn't happen this way. If a photon hit outside of the IBCO, then its trajectory is affected by the pull of the black hole, but it escapes the gravity well, and continues on a new trajectory elsewhere into space. After the photon hits the event horizon, then all statements needs a big asterisk with them. Its behavior might be observer-dependent or undefined. But at least in the conventional view of general relatively equations, it doesn't need to travel directly in the radial direction to the singularity, but it has to travel within a limited cone of possibilities, none of which lead back out. It can change its angular position somewhat as it gets closer to the singularity, but there is no orbit. No light cone within the event horizon allows for increasing the distance between a point particle and the singularity. In these conventional equations, all things that fall into the event horizon _hit_ the singularity within finite time according to a distant observer. Time has some shifty meaning to things inside of the event horizon, and maybe this is all wrong. But I am sure that orbiting the singularity inside the event horizon definitely does not happen.
Sargos 8y ago
I'm just a science fan and not an expert by any means but it appears that time simply stops at the event horizon for all intents and purposes. Things/light does not fall into the black hole as it just freezes at the event horizon... forever. There is no time in a black hole. Movement requires time.
TheLoneAdmin 8y ago
In circular motion, acceleration is always perpendicular to the velocity. While the velocity changes, the magnitude of the velocity (aka speed) stays constant.
bawana 8y ago
thank you for your replies. however, no one addressed the fact that as orbital radius decreases, velocity increases. and that should not be possible for light. In fact, the whole idea of light bending around a gravity well does not seem to follow the rules of orbital mechanics. Masses that come close to a massive body get a velocity boost and a slingshot to their new course. I would suspect that photons are boosted to a higher energy state and thus get a frequency boost as they are accelerated radially since they cannot get a speed boost. And more energetic photons would be more apt to return to a wider orbit-reaching an equilibrium of their orbital path.

by bawana 8y ago

l33tman 8y ago

The perfect orbit geodesic is infinitely thin and therefore unstable due to quantum mechanics. So even if a photon is injected at the perfect orbit it would not stay there, it would fall in or eject. Besides, even without invoking QM, any other matter that actually falls into the hole afterwards would inflate the event horizon, causing those photons caught in the perfect orbit to now exist just infinitesimally within the orbit and fall in.

soVeryTired 8y ago
Do you need quantum mechanics to see that a photon would fall in or eject? Presumably a little movement from the black hole would do the trick too.
- Pharmakon 8y ago
  Right, but the QM view tells us that even a perfectly stationary chargeless black hole in a perfect vacuum alone in a perfectly smooth universe would still experience fluctuations in its event horizon. Unlike the Classical view, QM reveals that even in principle there exists a degree of instability in the horizon.

AlanSE 8y ago

Light that comes within 3/2 of the Schwarzschild radius (Rs hereafter) gets captured by the black hole. Of course I don't mean that it beelines in a direct radial direction to the singularity. Of course it takes a curved path depending on its exact trajectory, but at some point on this trajectory it hits the event horizon. Nothing that hits the event horizon can ever come back out again (according to an observer at sufficient distance). This magic 3/2 Rs radius is the Innermost Bound Circular Orbit (IBCO), and is the truthfully correct scientific principle that you are grasping for. It is not a stable orbit, but it is an orbit. In a theoretical world, if a photon had the perfect trajectory to enter this orbit, it could orbit there indefinitely, but it is unstable, so in the real world it doesn't happen this way. If a photon hit outside of the IBCO, then its trajectory is affected by the pull of the black hole, but it escapes the gravity well, and continues on a new trajectory elsewhere into space. After the photon hits the event horizon, then all statements needs a big asterisk with them. Its behavior might be observer-dependent or undefined. But at least in the conventional view of general relatively equations, it doesn't need to travel directly in the radial direction to the singularity, but it has to travel within a limited cone of possibilities, none of which lead back out. It can change its angular position somewhat as it gets closer to the singularity, but there is no orbit. No light cone within the event horizon allows for increasing the distance between a point particle and the singularity. In these conventional equations, all things that fall into the event horizon _hit_ the singularity within finite time according to a distant observer. Time has some shifty meaning to things inside of the event horizon, and maybe this is all wrong. But I am sure that orbiting the singularity inside the event horizon definitely does not happen.

Sargos 8y ago

I'm just a science fan and not an expert by any means but it appears that time simply stops at the event horizon for all intents and purposes. Things/light does not fall into the black hole as it just freezes at the event horizon... forever. There is no time in a black hole. Movement requires time.

TheLoneAdmin 8y ago

In circular motion, acceleration is always perpendicular to the velocity. While the velocity changes, the magnitude of the velocity (aka speed) stays constant.

bawana 8y ago

thank you for your replies. however, no one addressed the fact that as orbital radius decreases, velocity increases. and that should not be possible for light. In fact, the whole idea of light bending around a gravity well does not seem to follow the rules of orbital mechanics. Masses that come close to a massive body get a velocity boost and a slingshot to their new course. I would suspect that photons are boosted to a higher energy state and thus get a frequency boost as they are accelerated radially since they cannot get a speed boost. And more energetic photons would be more apt to return to a wider orbit-reaching an equilibrium of their orbital path.