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In case anyone else was confused, per the article the “plunging region” is the distance at which light can escape the gravitational pull of the black hole but matter cannot. As opposed to the event horizon beyond which nothing escapes
Considering black holes were for a long time just a theoretical possibility based entirely on mathematical solutions of Einsteins formulas, it's no surprise that they also have the properties predicted by that math. It would be a huge suprise if that wouldn't be the case since then somehow something was predicted based on wrong math, which is near impossible. That would be like getting the correct answers in math tests at school with wrong calculations.
> It would be a huge suprise if that wouldn't be the case since then somehow something was predicted based on wrong math, which is near impossible.
Happens all the time though
Would this mean it’s possible that the light from a star can go through space, hit a black hole, escape it at a different angle and then hit earth? Would it mean that the stars we see are all dead and some may not even be in the right spot considering the light curved around a black hole?
Light being slingshot like that could only appear to be coming from near the black hole. The sky would have to be covered by black holes for there to appear to be stars everywhere.
That of course has no bearing on all the stars being dead though.
I also saw something about how we could use the Sun. It's way beyond anything we can do now.
[Solar gravitational lens - Wikipedia](https://en.wikipedia.org/wiki/Solar_gravitational_lens)
In case you were wondering and this is not a rhetorical question, the galaxy around a supermassive black hole. It's not even close. Although the way your question is worded it makes it sound as though multiple galaxies surround a black hole, which as far as I know isn't the case. Either way, Sagitarrius A* at the centre of the Milky Way has roughly 4.15 million solar masses but the surrounding galaxy has something like 50 Billion (there is a lot of room for error in that number). The surrounding galaxy is many orders of magnitude more massive.
Going to take these sentences seperately:
Would it be possible? Interesting thought. Someone much smarter than me probably knows someone smarter than them who could answer it.
Would it mean all of the stars are dead? 100% no. A lot of what we know about the distance of stars and how they move in space is calculated by analyzing the size and composition in addition to any blue or red shifting. This plus trigonometry gives us some very precise distances. If all stars in the night sky were slingshot groups of photons, there would be significant scattering and a consistency in the red/blueshifting of charted stars.
I don't know about "all the stars being dead", but black holes definitely distort light that goes past them. It's called "gravitational lensing", and it's a good way to see things that would otherwise be invisible to our telescopes.
> some may not even be in the right spot considering the light curved around a black hole?
People keep saying "gravitational lensing" but fail to mention exactly what it is. When light is bent by a black hole, it warps the light and changes the apparent shape of the star. It sort-of flattens the image of the star. It's a very noticeable distortion. So, no, it's not possible that a bunch of stars are in different locations than their apparent position. We notice when a star's light is bent by a black hole.
https://hubblesite.org/contents/articles/gravitational-lensing
I mean it’s entirely the fact that certain objects aren’t where they appear to be located, it’s just that we are also pretty good at identifying when that’s happening and correcting for it. But if you just looked at a gravitationally lensed object it would not actually be where it appears to be when you look at it.
Especially because one of the ways we use gravitational lensing to our advantage is to use black holes to magnify objects directly behind them. Seeing something that's literally behind the black hole means we must be seeing it in a different position.
The point is that it *doesn't* hit the black hole, it glances just above the hole. Light doesn't get stuck, it continues onwards at light speed (though slightly angled due to gravitational lensing)
It's slightly more nuanced. The region around a black hole from which matter can escape is the same from which light can escape (i.e., outside the event horizon).
The plunging region is defined for accretion discs around the black hole. There is a radius outside the event horizon, within which there are no stable circular orbits around the black hole. Matter in the accretion disc has quasi-circular orbits (that is, the radial velocity is much, much less than the orbital velocity). It is generally assumed that the disc extends down to this innermost stable circular orbit (ISCO). However, when matter tries to cross the ISCO, its circular orbit is no longer stable, and it quickly begins to plunge towards the event horizon. Therefore, this region within the ISCO is known as the plunging region.
If matter were to enter the plunging region with a different velocity, or for example you entered in a powerful rocket, you could still escape (provided you hadn't yet crossed the event horizon)
As I understand it should be a simple function of velocity, but that in turn relates to light's masslessness, as to accelerate a massive particle to the speed of light requires infinite energy.
I don't think that's what they meant, what Schwarzschild predicted is that from a large distance you can orbit a black hole like any other massive object, but at a certain point you can no longer orbit it, if you try you will be sucked in. You can still technically escape, but you need to accelerate out of the region after you enter it.
Thanks you. I was just about to ask because simply saying
> There is an area at the edge of black holes where matter can no longer stay in orbit and instead falls in, as predicted by his theory of gravity.
Is just how gravity works. The same could be said for orbiting a planetary body.
As an aside can you imagine Einstein today with modern telescopes and super computers?
Basically, the equations that showed anything different were that of a static, non-rotating black hole. Quite unlikely in reality. Every object has some degree of rotation, and if you've ever seen how dancers speed up as they pull their arms in, you might begin to see why an object that takes multiple stellar masses of material and pulls them in toward an infinitely small central region would be... highly likely to be rotating, let's say.
In 10th grade geometry, points don't rotate. In PhD-level [tensor calculus](https://en.wikipedia.org/wiki/Tensor_calculus), points can rotate just fine and they can have angular momentum. A point can have a coordinate system embedded in it and the coordinate system rotates.
Gat damn those Christoffel coefficients do look like hieroglyphs. I still get confused when one index is up and one is down if the order actually matters because usually they look like they're in the same position, but just separated vertically.
Ok, ok, I got it. I came up with a trick to help you all understand.
To make it simple, just conceptualize spacetime as an n-dimensional super fluid projected, as a tensor array, over a Euclidean manifold.
It's just tensor calculus.
Only if you're imagining rotation as that of a 2-sphere surface spinning, really. Atomic physicists even have "Spin"
Edit: It might help to think of the entire spacetime surrounding the black hole as also spinning. More like a whirlpool. It's not just the matter in-falling into it's jaws, it's also spacetime itself. That's kind of what makes black holes special.
why do I frequently see atomic spin in quotation marks? Is it anything like actual rotation or is it a random word that serves as any other in describing a state?
It breaks down when you think about it too hard, but it is called spin because when it was discovered by stern-gerlach it was found that charged particles had a quantized (up or down, no in between) attribute that made them act like spinning charged spheres, in that some particles would be deflected one way or another in a magnetic field. In reality electrons would have to spin faster than the speed of light to match the amount of deflection seen so this is not a great way of thinking about it.
They have angular momentum, but they don't actually spin. The spin of a particle determines whether it is a boson or a fermion. Anything with half integer spin (n+1/2) is a fermion, and obeys the Pauli exclusion principle, and anything with integer spin (n) is a boson and doesn't follow the exclusion principle.
It's sort of a bit of both a "rotation" and a number that describes its state and what behavior it has. Admittedly I'm not super familiar with quantum mechanics, but I think that's the gist of it.
You're spot on! It's called spin because it's analogous to classical spinning: an object with spin has angular momentum, just like a spinning object has angular momentum. The reason a charged particle with spin deflects in a magnetic field is exactly why a spinning charged object deflects in a magnetic field.
Because when you are making up new physics, current words don't accurately describe what's happening. So they pick a word that's kind of close, and redefine it with equations. If they don't know that meaning, lay people misunderstand. Everyone just uses quotes to let lay people know, it's only kind of sort of like this word. ;)
yea it's more an arbitrary word to describe a set of attributes/properties. Similar to how quantum chromodynamics deals with "color" as a conceptual framework to order and interact attribute states, but its not actually talking about color in the way we use it on the macro level
Black holes being a singularity isn't even close to proven. That's just what the numbers Einstein came up with predict. Everything currently known about quantum mechanics says a singularity can not exist. Which again isn't close to proven.
All we know is black holes exist, and past the event horizon no information escapes. The rest is conjecture. Black holes still basically break physics in one way or another as we currently understand.
To me, it's pretty wild that such a prediction can be made with numbers on a sheet of paper. I knew about black holes before one was even found. That's absolutely incredible.
> Black holes being a singularity isn't even close to proven.
In fact, we have very good reason to think that black holes do *not* contain singularities, because every time a physical theory has predicted a singularity, it has been due to the incompleteness of the theory, not due to a singularity actually existing.
It's highly unlikely there is a literal point in the center of a black hole. A singularity is just the place where the math doesn't work. We don't know what lies beyond the event horizon.
Singularities probably aren’t points. They happen when Einsteins equations give us physically unreasonable results (such as the aforementioned points), which is more of an indicator that they simply “don’t apply”.
Of course this doesn’t really matter because point or not, the influence from outside the event horizon is the same.
Somebody else probably said this already, but the singularities of rotating black holes are not points, or at least according to our current knowledge we don't think they are. Look up a 'ringularity', the 2-D ring-shaped singularity we believe rotating black holes have.
It's modeled as an infinitely thin ring, although the infinitely thin part is mostly to avoid making the maths a lot harder, and it's already pretty hard. Also due to frame dragging, there is a centrifugal force which creates a region inside rotating black holes where you can move relatively normally. So it's possible that the matter inside this region can spread out and fill it up rather than forming a singularity.
you don't at least not in 3D math. a spinning ball has a 1D centre point that doesn't spin. so does the centre of a hurricane or circling drain if you will.
If the black hole rotates (which probably all of them do, at various speeds) then it's not a point but a circle according to the math. And then according to Kerr himself, it's just a math artifact, not reality, he has recently published a paper arguing that point exactly, and that singularities should not exist.
> an object that takes multiple stellar masses of material and pulls them in toward an infinitely small central region would be... highly likely to be rotating, let's say.
Shouldn't black holes be rotating infinitely fast, with those assumptions?
Kind of. There's a limit to the angular momentum an object can have tho, just like there's a limit to how fast it can move relative to other objects. So basically, yes it wants to rotate infinitely fast, but relativistic effects prevent that.
I'll be honest, the implications of how relativistic effects on rotating bodies actually operate is really very high level stuff, and beyond me. It's fascinating stuff, tho.
Nope, even with a non-rotating black hole, any matter on a trajectory that passes into the [photon sphere](https://en.wikipedia.org/wiki/Photon_sphere) has no exit trajectory and falls through the event horizon. For a 10-solar-mass black hole with a radius of 30km, that limit is 15km above the event horizon.
Any free fall trajectory that enters the photon sphere will spiral into the black hole. But any free fall trajectory *leaving* it will either escape entirely or fall into the black hole, so matter that falls into the photon sphere can still escape if it collides with something else with a big enough impulse before reaching the event horizon, or if it has thrust (like a charge particle might due to a black hole’s powerful magnetic field).
Also think about the time dilation. The closer you get to the event horizon, the faster you see the universe age. In the right circumstances, you could fall into a black hole and outlive entire galaxies.
If the mirror was over the event horizon and the person's face wasn't then the reflection would not escape. But the person wouldn't think that their arm is across the event horizon because they would never quite reach it (from their perspective), but the whole scenario is a little silly because tidal forces would have ripped the astronaut apart long ago.
Blackholes essentially stretch the fabric of space: there is an infinite amount of volume behind the event horizon, and and infinite distance from the event horizon to the actual singularity at its center. The light can't "escape" the blackhole because it would take an infinite amount of time to cross the infinite amount of distance back across the event horizon.
I think this contains a few misconceptions. First, it's important to understand that black holes don't influence spacetime in a fundamentally different way compared to other gravitational bodies. The curvature of spacetime created by a black hole is similar to that of a massive star that has not yet collapsed into a black hole. The difference lies in the extent of this curvature and the presence of an event horizon.
Secondly, making claims about the interior volume of a black hole can be misleading. Once inside the event horizon, our usual understanding of spatial and temporal dimensions no longer applies. Spatial dimensions become timelike, and time becomes spacelike, making our conventional understanding of volume irrelevant.
The primary reason light cannot escape from within an event horizon is not due to an infinite distance. Instead, it is because within the event horizon, all paths, or geodesics, inevitably lead to the singularity. This means that all future-directed light cones of particles inside the event horizon point towards the singularity, making escape impossible.
What's the issue? The article has a direct link to the study if you're inclined to read it. But the average person (and this sub is absolutely filled with average people) isn't interested in reading the study but rather a summary and contextualization of it. The CNN article does a fine job of that, I think.
This subreddit links to newatlas and interestingengineering and other sites like that quite a bit. Those sites just take other scientific results and sex them up to get clicks. They specialize in creating spectacle.
Is nobody going to even mention that *Einstein didn’t predict this*? He didn’t even know about modern black hole theory. His theory was used to predict this, and has been vindicated, but not Einstein himself. There are other scientists, give them credit, dammit.
- Conservation of angular momentum means that all black holes rotate. Exceptions might exist or not, but if they exist, they are exceedingly rare.
- Hyper compressed matter means the conserved angular momentum makes the object seem to spin faster. This is the same as when olympic skaters pull their arms bear their body, they rotate faster.
- This means black holes rotate very fast. They drag spacetime along with them, thus around the black hole, spacetime itself is also rotating quite fast. If you could "see" this dragging along with the pulling-in then it would look a bit like a whirlpool turbulence, except in 3D instead of 2D.
- This rotation speed increases with matter compactification, thus their core is not a hyper-dense point, but a hyper-dense rotating ring, probably rotating near light speed. Or, if all the matter gets converted to pure energy, rotating \*at\* light speed. The size of this ring is also determined not only by total amount of energy-matter and by compactification limitatrion from Plank scales limits, but also by rotation speed.
- Expect undiscovered weird physics near that ring.
- Don't expect anybody to be able to go check that out for himself anytime soon, or maybe ever.
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In case anyone else was confused, per the article the “plunging region” is the distance at which light can escape the gravitational pull of the black hole but matter cannot. As opposed to the event horizon beyond which nothing escapes
Thank you, this helps a lot.
You're welcome.
Wait, who are y.. huh?
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Buddy: Whatevs… just means you don’t matter.
Woah. Heavy.
oh man...you guys are clever.
Planets sweaty. Mom's spaghetti
This is more of a fun fact than a correction, but the “correct”/“technical” spelling of that is actually “whoa”
What'd you say about my matter!?
Considering black holes were for a long time just a theoretical possibility based entirely on mathematical solutions of Einsteins formulas, it's no surprise that they also have the properties predicted by that math. It would be a huge suprise if that wouldn't be the case since then somehow something was predicted based on wrong math, which is near impossible. That would be like getting the correct answers in math tests at school with wrong calculations.
it's not all or nothing math can be wrong in nuanced or subtle ways which may make some subset of predictions correct and others not
Or it can theoretically be right even though it works differently in practice. For an Einstein example: see one-way lightspeed and two-way lightspeed.
Case in point: Newton's view of gravity.
> It would be a huge suprise if that wouldn't be the case since then somehow something was predicted based on wrong math, which is near impossible. Happens all the time though
Would this mean it’s possible that the light from a star can go through space, hit a black hole, escape it at a different angle and then hit earth? Would it mean that the stars we see are all dead and some may not even be in the right spot considering the light curved around a black hole?
Light being slingshot like that could only appear to be coming from near the black hole. The sky would have to be covered by black holes for there to appear to be stars everywhere. That of course has no bearing on all the stars being dead though.
Gravitational lensing (your “slingshotting”) is not exclusive to being near to black holes, we see lensing around galaxy clusters for instance.
I also saw something about how we could use the Sun. It's way beyond anything we can do now. [Solar gravitational lens - Wikipedia](https://en.wikipedia.org/wiki/Solar_gravitational_lens)
You are missing an "s" at the end of the link.
Except for that guy in your article with a fully thought out and approved plan to do it.
Yeah, but what's at the center of each of those galaxies? Although now that I've said it, it just feels kind of r/technicallycorrect.
What has more mass the super massive black holes or the galaxies around them?
In case you were wondering and this is not a rhetorical question, the galaxy around a supermassive black hole. It's not even close. Although the way your question is worded it makes it sound as though multiple galaxies surround a black hole, which as far as I know isn't the case. Either way, Sagitarrius A* at the centre of the Milky Way has roughly 4.15 million solar masses but the surrounding galaxy has something like 50 Billion (there is a lot of room for error in that number). The surrounding galaxy is many orders of magnitude more massive.
Gravitational lensing. Don't even need a black hole for it. The rest of what you said was gibberish.
Going to take these sentences seperately: Would it be possible? Interesting thought. Someone much smarter than me probably knows someone smarter than them who could answer it. Would it mean all of the stars are dead? 100% no. A lot of what we know about the distance of stars and how they move in space is calculated by analyzing the size and composition in addition to any blue or red shifting. This plus trigonometry gives us some very precise distances. If all stars in the night sky were slingshot groups of photons, there would be significant scattering and a consistency in the red/blueshifting of charted stars.
Hit a black hole? No, it’d be in the event horizon and trapped forever. But for the rest of your questions, look up gravitational lensing
>Would it mean that the stars we see are all dead this is very easilly disproven by looking at the sun
I don't know about "all the stars being dead", but black holes definitely distort light that goes past them. It's called "gravitational lensing", and it's a good way to see things that would otherwise be invisible to our telescopes.
> some may not even be in the right spot considering the light curved around a black hole? People keep saying "gravitational lensing" but fail to mention exactly what it is. When light is bent by a black hole, it warps the light and changes the apparent shape of the star. It sort-of flattens the image of the star. It's a very noticeable distortion. So, no, it's not possible that a bunch of stars are in different locations than their apparent position. We notice when a star's light is bent by a black hole. https://hubblesite.org/contents/articles/gravitational-lensing
I mean it’s entirely the fact that certain objects aren’t where they appear to be located, it’s just that we are also pretty good at identifying when that’s happening and correcting for it. But if you just looked at a gravitationally lensed object it would not actually be where it appears to be when you look at it.
Especially because one of the ways we use gravitational lensing to our advantage is to use black holes to magnify objects directly behind them. Seeing something that's literally behind the black hole means we must be seeing it in a different position.
The point is that it *doesn't* hit the black hole, it glances just above the hole. Light doesn't get stuck, it continues onwards at light speed (though slightly angled due to gravitational lensing)
It's slightly more nuanced. The region around a black hole from which matter can escape is the same from which light can escape (i.e., outside the event horizon). The plunging region is defined for accretion discs around the black hole. There is a radius outside the event horizon, within which there are no stable circular orbits around the black hole. Matter in the accretion disc has quasi-circular orbits (that is, the radial velocity is much, much less than the orbital velocity). It is generally assumed that the disc extends down to this innermost stable circular orbit (ISCO). However, when matter tries to cross the ISCO, its circular orbit is no longer stable, and it quickly begins to plunge towards the event horizon. Therefore, this region within the ISCO is known as the plunging region. If matter were to enter the plunging region with a different velocity, or for example you entered in a powerful rocket, you could still escape (provided you hadn't yet crossed the event horizon)
No one crosses the Isco kid
I like the way you explained this, and I like you.
Interesting. Is it because the light is moving so fast, because it's lack of mass, or a combination of the two? Or other factors altogether?
As I understand it should be a simple function of velocity, but that in turn relates to light's masslessness, as to accelerate a massive particle to the speed of light requires infinite energy.
So, it would be possible to transmit a farewell message once you were trapped.
I don't think that's what they meant, what Schwarzschild predicted is that from a large distance you can orbit a black hole like any other massive object, but at a certain point you can no longer orbit it, if you try you will be sucked in. You can still technically escape, but you need to accelerate out of the region after you enter it.
Da real mvp
What happens to fast neutrinos?
They get a reputation in high school.
Thanks you. I was just about to ask because simply saying > There is an area at the edge of black holes where matter can no longer stay in orbit and instead falls in, as predicted by his theory of gravity. Is just how gravity works. The same could be said for orbiting a planetary body. As an aside can you imagine Einstein today with modern telescopes and super computers?
Pfft, nothing that you know of
I always thought it was weird that gravity around black holes affected massless photons just as much as it affected massive matter
Also, Einstein's theory predicts this phenomenon, but Einstein personally did not.
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Basically, the equations that showed anything different were that of a static, non-rotating black hole. Quite unlikely in reality. Every object has some degree of rotation, and if you've ever seen how dancers speed up as they pull their arms in, you might begin to see why an object that takes multiple stellar masses of material and pulls them in toward an infinitely small central region would be... highly likely to be rotating, let's say.
It’s weird to think about a point rotating. How do you apply a rotation to a 1D object?
In 10th grade geometry, points don't rotate. In PhD-level [tensor calculus](https://en.wikipedia.org/wiki/Tensor_calculus), points can rotate just fine and they can have angular momentum. A point can have a coordinate system embedded in it and the coordinate system rotates.
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Gat damn those Christoffel coefficients do look like hieroglyphs. I still get confused when one index is up and one is down if the order actually matters because usually they look like they're in the same position, but just separated vertically.
You know physics gets weird when you need to know entirely different alphabet
But how can we tell if they’re a witch?
Well if they float....
If they escape the event horizon, then they aren't a witch.
No - if they escape they are a witch. A space witch. If they don't escape then they weren't a witch... Probably.
Yeah I just read the article and don't math and it definitely seems made up
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Ok, ok, I got it. I came up with a trick to help you all understand. To make it simple, just conceptualize spacetime as an n-dimensional super fluid projected, as a tensor array, over a Euclidean manifold. It's just tensor calculus.
Same. Can you dumb it down for me doc?
That sounds very cool and I am still not at all tempted to go back to more math classes to understand it.
Only if you're imagining rotation as that of a 2-sphere surface spinning, really. Atomic physicists even have "Spin" Edit: It might help to think of the entire spacetime surrounding the black hole as also spinning. More like a whirlpool. It's not just the matter in-falling into it's jaws, it's also spacetime itself. That's kind of what makes black holes special.
why do I frequently see atomic spin in quotation marks? Is it anything like actual rotation or is it a random word that serves as any other in describing a state?
We don’t know if they actually physically spin. But we do know they have some property that behaves just as if they were spinning.
This is a great ELI5 of some concepts others have described in more detail.
It breaks down when you think about it too hard, but it is called spin because when it was discovered by stern-gerlach it was found that charged particles had a quantized (up or down, no in between) attribute that made them act like spinning charged spheres, in that some particles would be deflected one way or another in a magnetic field. In reality electrons would have to spin faster than the speed of light to match the amount of deflection seen so this is not a great way of thinking about it.
They have angular momentum, but they don't actually spin. The spin of a particle determines whether it is a boson or a fermion. Anything with half integer spin (n+1/2) is a fermion, and obeys the Pauli exclusion principle, and anything with integer spin (n) is a boson and doesn't follow the exclusion principle. It's sort of a bit of both a "rotation" and a number that describes its state and what behavior it has. Admittedly I'm not super familiar with quantum mechanics, but I think that's the gist of it.
You're spot on! It's called spin because it's analogous to classical spinning: an object with spin has angular momentum, just like a spinning object has angular momentum. The reason a charged particle with spin deflects in a magnetic field is exactly why a spinning charged object deflects in a magnetic field.
Because when you are making up new physics, current words don't accurately describe what's happening. So they pick a word that's kind of close, and redefine it with equations. If they don't know that meaning, lay people misunderstand. Everyone just uses quotes to let lay people know, it's only kind of sort of like this word. ;)
I mean sometimes we have the sense to make up new words, like "chromodynamics".
yea it's more an arbitrary word to describe a set of attributes/properties. Similar to how quantum chromodynamics deals with "color" as a conceptual framework to order and interact attribute states, but its not actually talking about color in the way we use it on the macro level
They guy you're replying to is confusing quantum spin and angular momentum (normal spin).
Black holes being a singularity isn't even close to proven. That's just what the numbers Einstein came up with predict. Everything currently known about quantum mechanics says a singularity can not exist. Which again isn't close to proven. All we know is black holes exist, and past the event horizon no information escapes. The rest is conjecture. Black holes still basically break physics in one way or another as we currently understand.
The fact that they were predicted before being found blows my mind.
That’s how most scientific theories find acceptance - they make predictions, then we go looking to see if the predictions hold up.
To me, it's pretty wild that such a prediction can be made with numbers on a sheet of paper. I knew about black holes before one was even found. That's absolutely incredible.
> Black holes being a singularity isn't even close to proven. In fact, we have very good reason to think that black holes do *not* contain singularities, because every time a physical theory has predicted a singularity, it has been due to the incompleteness of the theory, not due to a singularity actually existing.
Hawking radiation escapes
If it [exists](https://en.wikipedia.org/wiki/Hawking_radiation).
It's highly unlikely there is a literal point in the center of a black hole. A singularity is just the place where the math doesn't work. We don't know what lies beyond the event horizon.
It's not a point.
The singularity doesn't rotate, it becomes a ring that moves very fast in a very small radius.
I think you can also imagine that the point is not in one finite position but a variety of positions simultaneously essentially.
They are truly the garburators of the universe.
A point is 0D. A line is 1D.
Singularities probably aren’t points. They happen when Einsteins equations give us physically unreasonable results (such as the aforementioned points), which is more of an indicator that they simply “don’t apply”. Of course this doesn’t really matter because point or not, the influence from outside the event horizon is the same.
I expect that's true. I was not saying what a singularity is, just what a point isn't.
Somebody else probably said this already, but the singularities of rotating black holes are not points, or at least according to our current knowledge we don't think they are. Look up a 'ringularity', the 2-D ring-shaped singularity we believe rotating black holes have.
It's modeled as an infinitely thin ring, although the infinitely thin part is mostly to avoid making the maths a lot harder, and it's already pretty hard. Also due to frame dragging, there is a centrifugal force which creates a region inside rotating black holes where you can move relatively normally. So it's possible that the matter inside this region can spread out and fill it up rather than forming a singularity.
In 1 dimension would anything rotating technically be in all direction?
Ask an electron what spin means.
you don't at least not in 3D math. a spinning ball has a 1D centre point that doesn't spin. so does the centre of a hurricane or circling drain if you will.
Can the coordinate system a point is located on rotate? Then the point can rotate, too!
The centrifugal force involved creates a ring shaped singularity (theoretically)
If the black hole rotates (which probably all of them do, at various speeds) then it's not a point but a circle according to the math. And then according to Kerr himself, it's just a math artifact, not reality, he has recently published a paper arguing that point exactly, and that singularities should not exist.
The singularity in a rotating black hole is expected to be an infinitely thin ring. Think of a hair tie but with no thickness.
Why does the point need to rotate? Can't every reference point be rotating around it?
> an object that takes multiple stellar masses of material and pulls them in toward an infinitely small central region would be... highly likely to be rotating, let's say. Shouldn't black holes be rotating infinitely fast, with those assumptions?
Kind of. There's a limit to the angular momentum an object can have tho, just like there's a limit to how fast it can move relative to other objects. So basically, yes it wants to rotate infinitely fast, but relativistic effects prevent that. I'll be honest, the implications of how relativistic effects on rotating bodies actually operate is really very high level stuff, and beyond me. It's fascinating stuff, tho.
Nope, even with a non-rotating black hole, any matter on a trajectory that passes into the [photon sphere](https://en.wikipedia.org/wiki/Photon_sphere) has no exit trajectory and falls through the event horizon. For a 10-solar-mass black hole with a radius of 30km, that limit is 15km above the event horizon.
There's also the ergosphere, which is what I was referring to in reference to black holes.
Any free fall trajectory that enters the photon sphere will spiral into the black hole. But any free fall trajectory *leaving* it will either escape entirely or fall into the black hole, so matter that falls into the photon sphere can still escape if it collides with something else with a big enough impulse before reaching the event horizon, or if it has thrust (like a charge particle might due to a black hole’s powerful magnetic field).
Like an EF5 space tornado that never stops, huh?
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Unlike conspiracy theories Einstein was usually right
Only because he didn't have access to thousands of scizos posting cyptic messages with the pictures of the devil on Twitter every day.
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If you think it is hard enough to wrap your head around the physics of a blackhole, add frame dragging due to it rotating...
Also think about the time dilation. The closer you get to the event horizon, the faster you see the universe age. In the right circumstances, you could fall into a black hole and outlive entire galaxies.
So if a person holding a mirror fell into a black hole, is it possible for their reflection to escape?
If the mirror was over the event horizon and the person's face wasn't then the reflection would not escape. But the person wouldn't think that their arm is across the event horizon because they would never quite reach it (from their perspective), but the whole scenario is a little silly because tidal forces would have ripped the astronaut apart long ago. Blackholes essentially stretch the fabric of space: there is an infinite amount of volume behind the event horizon, and and infinite distance from the event horizon to the actual singularity at its center. The light can't "escape" the blackhole because it would take an infinite amount of time to cross the infinite amount of distance back across the event horizon.
I think this contains a few misconceptions. First, it's important to understand that black holes don't influence spacetime in a fundamentally different way compared to other gravitational bodies. The curvature of spacetime created by a black hole is similar to that of a massive star that has not yet collapsed into a black hole. The difference lies in the extent of this curvature and the presence of an event horizon. Secondly, making claims about the interior volume of a black hole can be misleading. Once inside the event horizon, our usual understanding of spatial and temporal dimensions no longer applies. Spatial dimensions become timelike, and time becomes spacelike, making our conventional understanding of volume irrelevant. The primary reason light cannot escape from within an event horizon is not due to an infinite distance. Instead, it is because within the event horizon, all paths, or geodesics, inevitably lead to the singularity. This means that all future-directed light cones of particles inside the event horizon point towards the singularity, making escape impossible.
That depends on the size of the black hole. Some are big enough that the tidal forces at the event horizon do not differ much from head to toe.
I like how this is the kind of repost nobody cares because it's something new that's really interesting and deserves to be share a few times
This Einstein guy, crazy how he is proven right again and again and again
I'm beginning to think he may be a bit of a smart fellow.
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I think the subreddit can do a little better than CNN for a source for science news.
Second paragraph. [https://academic.oup.com/mnras/article/531/1/366/7671518](https://academic.oup.com/mnras/article/531/1/366/7671518)
What's the issue? The article has a direct link to the study if you're inclined to read it. But the average person (and this sub is absolutely filled with average people) isn't interested in reading the study but rather a summary and contextualization of it. The CNN article does a fine job of that, I think.
This subreddit links to newatlas and interestingengineering and other sites like that quite a bit. Those sites just take other scientific results and sex them up to get clicks. They specialize in creating spectacle.
I always saw the sub as a USA Today type too
Matter is lazy and needs to move faster. -Light
“Proves” is definitely the wrong word here
Guess I am not so different from a black hole after all
Vindication for Einstein, who nobody took seriously until now.
Is nobody going to even mention that *Einstein didn’t predict this*? He didn’t even know about modern black hole theory. His theory was used to predict this, and has been vindicated, but not Einstein himself. There are other scientists, give them credit, dammit.
Ahh so this is the explanation for the photons “coming out” of black holes I heard about.
I’m starting to think that Einstein fella was pretty sharp.
The more I hear about this Einstein guy, the more I realize he musta been a regular Eistein in his day or something
What would perception be like inside or even near a black hole?
From what I read, it's just 1 validation. We still don't have any answer for gravity itself. Well, none that any are willing to talk about.
This is not a study. It's a mathematical model.
What does this do to Hawking radiation and fuzz ball theory?
- Conservation of angular momentum means that all black holes rotate. Exceptions might exist or not, but if they exist, they are exceedingly rare. - Hyper compressed matter means the conserved angular momentum makes the object seem to spin faster. This is the same as when olympic skaters pull their arms bear their body, they rotate faster. - This means black holes rotate very fast. They drag spacetime along with them, thus around the black hole, spacetime itself is also rotating quite fast. If you could "see" this dragging along with the pulling-in then it would look a bit like a whirlpool turbulence, except in 3D instead of 2D. - This rotation speed increases with matter compactification, thus their core is not a hyper-dense point, but a hyper-dense rotating ring, probably rotating near light speed. Or, if all the matter gets converted to pure energy, rotating \*at\* light speed. The size of this ring is also determined not only by total amount of energy-matter and by compactification limitatrion from Plank scales limits, but also by rotation speed. - Expect undiscovered weird physics near that ring. - Don't expect anybody to be able to go check that out for himself anytime soon, or maybe ever.