Black hole

[Imperator Romani]

Ok scientists. Here's a question for you.

If you get sucked into a black hole, will you ever hit the dense matter at the heart of it? I know that it sounds like an obvious answer, but, think about this.

I'm not a scientist but I'll explain it the best I can, hopefully you will get the jist.

Matter going into the black hole is going at the speed of light, hence the capture of light that makes it a black hole. BUT the light never reaches it, as you get closer to the dense matter you will go slower and slower, which is why light never reaches it and reflects off of it. Will you ever eventually stop?

Can someone answer my first question and tell me why you get slower the closer you get.

[finsternis]

Actually, the reason why light does not escape is because of the strong gravitational force.

As for why you get slower, well when you travel at (or near) the speed of light time would look to go slower from an outsider's perspective.

But if I remember, that is not the reason why you can look into the future when in a black hole (meaning, go slow). I can't remember the actual reason .
I remember reading about it but I forgot.

[Frédéric Chopin]

From my understanding of black holes, your description isn't entirely correct. The matter going into a black hole isn't going at the speed of light as that would be impossible due to relativity. The reason light cannot escape is, as finsternis said, that the gravitational field is too powerful. The light does, in fact, hit the singularity and does not reflect off. That's why they're called black holes, they don't reflect anything (like a perfect blackbody). From the perspective of the observer falling into the black hole, it would pass through the event horizon, the boundary beyond which it would be impossibe to escape, and fall quickly to the singularity at the centre of the black hole. However, because the mass off the black hole affects spacetime, an observer not falling into the black hole would view things differently; this is the reason for "seeing the future" or "slowing down." This observer would see you come to a complete stop before falling to the singularity. In effect, time for the person not falling into the black hole passes infinitely faster than time for the one falling. So the effect of seeing the future would be because, falling into the black hole, you see time passing by much more quickly when you look out from the black hole.

I hope this made sense, writing about relativity this late at night sure is confusing.

[jumong]

thanks for the explaination frederic.

[Imperator Romani]

Thank you for helpin me understand. Still don't know why it's called a hole though(maybe because of the properties?). + rep to both, unless you don't want it haha.

[Baron von Sky Hat]

Frederics explanation is mostly right, to the best of my knowledge. The talk of surfaces though isn't strictly ideal to explain it, as the singularity doesn't really have a surface, and the event horizon is just a point with a certain ratio of parameters, rather than anything physically there. I think that this is what you meant anyway, but thought I'd mention. As I said, you explained most of it, so sorry if I repeat stuff that you did cover, I'm just following my own monologue of explanation.

PureInfantryWins, your initial confusion about the situation (material moving at/near C when getting to the black hole) is likely understandable for someone without much background knowledge of the field. Time dilation is one of the main things people know about black holes, and it kind of has two causes (they're actually very closely related, rather than two distinctly complete separate effects), that of moving very fast (explained mostly by special relativity) and being near an extremely large mass (explained mostly in general relativity). So understanding of special relativity, combined with knowing the effects of time dilation with black holes would potentially imply the material needing to move fast in order to behave like it should.

However, Of these it's the latter, mass and general relativity, that is at play with material entering a black hole. The black hole can be thought of as two main pieces, the black hole itself (point of infinite density, and mass of whatever became the black hole in the first place), and its event horizon.
The event horizon isn't a physical thing, and needn't even be a sphere or similar (if the black hole is rotating, the shape of the event horizon is different). For a non-rotating black hole, the event horizon is at a distance called the Schwarzschild radius (r = 2 G m / c^2 ; G = grav. constant, m = mass of object, c = speed of light). At this point any particle or photon of light is drawn inwards towards the black hole faster than it can possibly move out, the object, light, or any light subsequently emitted by the object, is trapped, and can only fall into the singularity.

The rest of what I say I'm less certain on, it's not the field that I'm actively in, so I've bits and pieces of my prior university physics degree to recall... I may need some correcting, and if I find time, I'll look it up in more detail to correct stuff myself. That disclaimer said:

As far as I'm aware, it has been shown that any masses will fall inwards and contact the singularity in a non-infinite time, and that they would experience extreme time dilation as they fell, so everything else would appear to move through time quicker than them (anything further out than they were, anyway, anything closer to the blackhole than the object, even within the event horizon would appear similarly black, as to anyone observing the event horizon itself.) However it means they would reach the centre, they wouldn't get `stuck' in time at an intermediate point.

Lets say that the object falling towards the bh is a clock, and at a fair distance we, the observer, have our own clock. The basic idea is that the closer the falling clock gets to the large mass of the black hole, the slower it would appear to us to be going. As far as the falling clock is concerned, I'm not actually sure, you'd think that it would see us going much much faster, however I'm not sure that's the case. For a special relativity analogue, when something is travelling fast relative to another thing, they both think that the other is going slower, there's a symmetry to it because there's no distinction between thing A moving relative to thing B, or thing B moving relative to thing A. I'm not sure if it's similar with general relativity and masses, though. Therefore I think that it is different, but it's a while since I've covered anything like this though, and can't recall enough, I may need to check.

As the falling clock gets to the event horizon, it would have some of the same effects as though you were moving very fast away from it (or vice versa), light from it would be redshifted, and less would come towards you (some would be bent towards the bh), so it would appear to redden and get duller until disappearing at the event horizon itself.
Beyond the event horizon, I'm even less certain of what happens. The falling clock (assuming it can see at all...) wouldn't be able to see anything ahead of it, towards the bh (nothing can move outwards at all). I would presume things behind it would appear blueshifted and bright.

As to the exact process that occurs as any particles reach the singularity, I'm not sure at all. I don't know all that much about the field, and what is known through study of general relativity would be uncertain due to the nature of the problem: It's something we don't really have the ability to test.

The other problem with talking about an actual `thing' reaching and going through an event horizon is the material strength of that thing. Certainly any conventional object would disintegrate under tidal forces as it got closer, probably well before even reaching the event horizon (tidal disruption is where the gravity on the near-side of the object from the black hole(/other large mass) is different enough from the gravity of the far-side of the object that the difference in force overcomes the forces holding it together and it breaks apart. The comet Shumaker Levy 9 was broken apart by tidal forces due to Jupiters gravity before it reached the surface and impacted.)

One interesting thing that people seem to think is that a black hole will just pull everything in, regardless of the initial configuration of the system. For example, I imagine that if you ask someone what would happen to the earth if the sun became a black hole (excluding the actual process that causes a black hole, which involves lots of initial energy release and stuff), would be that the earth would get sucked in. It wouldn't, since the black hole would have the same mass as the sun (again, assuming it spontaneously became a black hole, actual systems would likely result in a bh with less mass than the original star, as mass is ejected in the process), so the earth would continue on its orbit.

I think that certain properties of a black hole system with things orbiting it do have processes by which angular momentum of the orbiting objects can be transferred to the black hole, resulting in the orbital radius decreasing. Though these wouldn't be like normal binary stars with decreasing orbital radii (stellar wind resistance and such), so I'm not sure what they would be, I'll have to check.

The centre of our galaxy has a `supermassive' black hole, with a mass in the region of a million times the mass of our sun, it's theorised that all galaxies have one, forming the centerpoint of mass which permits matter to clump into the galaxy in the first place (or as a result of initial clumping, and simply being dense enough at the centre to make a black hole). Our's has several stars orbiting it, one of which is very close to it (a matter of light hours), so we can map their orbits, and look at the point they should be orbiting, and there's nothing visible there, as you'd expect from a non-accreting black hole.

In some galaxies, the black hole is `accreting', matter is actively falling into it (unlike ours) and past the event horizon. These are called AGNs, Active Galactic Nuclei. They emit large amounts of the radiation due to the effects of heating and several other physical effects as a steam of matter, likely the tidally ripped apart remnants of a star, spiral inwards.

Anyway, I wrote more than I intended to, without actually checking whether I was actually answering questions or just ranting about black holes. It's probably mostly rant (possibly inaccurate rant, nonetheless), though hopefully interesting either way. I'll attempt to correct any mistakes I might find, or hopefully someone more knowledgeable can correct and expand upon all of this.

[finsternis]

PureInfantryWins, your initial confusion about the situation (material moving at/near C c when getting to the black hole) is likely understandable for someone without much background knowledge of the field.

Just a little correction
lol

Lets say that the object falling towards the bh is a clock, and at a fair distance we, the observer, have our own clock. The basic idea is that the closer the falling clock gets to the large mass of the black hole, the slower it would appear to us to be going. As far as the falling clock is concerned, I'm not actually sure, you'd think that it would see us going much much faster, however I'm not sure that's the case. For a special relativity analogue, when something is travelling fast relative to another thing, they both think that the other is going slower, there's a symmetry to it because there's no distinction between thing A moving relative to thing B, or thing B moving relative to thing A. I'm not sure if it's similar with general relativity and masses, though. Therefore I think that it is different, but it's a while since I've covered anything like this though, and can't recall enough, I may need to check.

Remember that special relativity only applies for constant velocities (inertial frames).
In a black hole, you are always accelerating. I think that that's the reason why one seems to be going slow while the other fast (the one in the black hole is in a non-inertial frame of reference because of the ever changing strength of gravity).


...or so I think. I haven't taken that class yet.

@Godfrey:

All of your mass gets transformed into x-ray (or did they disprove that already?).

I remember reading that black holes can throw out x-ray (not sure how though).

[Baron von Sky Hat]

Just a little correction
lol



Remember that special relativity only applies for constant velocities (inertial frames).
In a black hole, you are always accelerating. I think that that's the reason why one seems to be going slow while the other fast (the one in the black hole is in a non-inertial frame of reference because of the ever changing strength of gravity).


...or so I think. I haven't taken that class yet.

@Godfrey:

All of your mass gets transformed into x-ray (or did they disprove that already?).

I remember reading that black holes can throw out x-ray (not sure how though).

Oops, quite right about C -> c


As you say, special relativity does indeed only apply for non-accelerating frames (as illustrated by the fact that special relativity appears to create a paradox in the `twins paradox' with one of a pair of identical twins going at near c to a nearby planet and back, and seeming as though their ages would be different on his return). However, I didn't mean to apply special relativity itself, only relating the implied symmetry in special, regarding there being no importance on who is observing who, since I'm not sure how it would play out in general rel. with the black hole specifically. A reference frame with the black hole being `stationary' (or effectively stationary, a sufficiently far away observer), and a reference frame with the falling object. Whether they should each expect to observe the same effects on the other. As I said, I don't know general relativity very well at all, ideally someone who does could explain this process in particular.

The mass doesn't just get transformed into x-rays as such, there will still be mass travelling past the event horizon and on to the black hole itself. There are x-rays (and other areas of the spectrum) emitted by material as it falls in though. The AGN example I gave at the end is exactly that, due to heating and numorous effects (indirect illumination of cold nearby material by radiation from the falling object, synchotron radiation, etc) with the extreme pressures and temperatures the material is put to as it falls in.

Due to conservation of angular momentum, as with accreting binay star systems, you tend to get a disc forming out of whatever material is being accreted. At the middle you tend to get streams of matter falling in from the rest of the disc, emitting strongly beamed radiation as it goes towards the event horizon. AGNs seem to probably have a fairly complex geometry in at least some cases, with a disc, and torus of material as well, and potentially a further out surrounding shell like cloud of dust and gas. Some forms of processes resulting from the spiralling material would indeed produce x-rays.

The general ideas of physical transport to another location via a black hole relies on a number of things. I don't know much of the theory specifics in great detail, but I think the most quoted idea is that of an `Einstein-Rosen Bridge', where, if you imagine the images representing space-time around a black hole, looking like a funnel; that funnel after constricting inwards, opens out again at another location in space-time, such that a black hole and `white hole' are connected. It seems as though such is mathematically plausible, but I'm not aware of existance of any observational evidence of white holes.

As I said, I don't know a great amount about the theory, but I think that it's not the way people interpret it, such that you could actually send something through and out to the other side. More that it is a link by which information can be sent, radiation, particles possibly, but you couldn't travel through one in the TV/film wormhole type way. I may be wrong though, and it is just a theory, I don't think any direct proof of any kind has shown their existance.

Since you fall apart well before reaching near the black hole through the sort of processes that you'd get from any large mass, there's no particular reason to believe that any object would be reconstructed on the other side.

The other problem with travel, although again, I'm not certain on this. Is that I would imagine that Hawking Radiation (emitted from the black hole itself, preventing the complete loss of `information' of things that fall into the actual singularity... I think...), could possibly imply that the matter isn't actually going anywhere other than the black hole? Depending on the manner in which Hawking radiation is created and works, I don't know many specifics about it at all.

On the matter of whether it's a valid question, I very much think it is. While practically we know that, almost certainly, you would die before reaching it, the concept of an object reaching it isn't innately invalid. You can consider just a single particle, there will be things happening relative to that particle in the same situations as an object falling in, even though the particle won't actually see or experience them. There are plenty of uses of scientific speculation and thought experiments that couldn't actually physically happen, but that are very useful tools to analyse the theory surrounding certain ideas.

[Holger Danske]

Rather irrelevant. You'll die because of the insane gravitational forces way before that point, so who cares really?...

[Godfrey I of Leuven]

You could die.. Though what happens after you're inside a black hole no one knows.

[Holger Danske]

You could die.. Though what happens after you're inside a black hole no one knows.

Your body is made for 1G enviroment. Imagine what happens if you swap 1G with a infinite (or thereabout) number of G's... Carnage.

[Godfrey I of Leuven]

Well the thing is you could as well be 'put back together' on the other side, if there is an other side that is. I also read once that some people connect the multiversum theory with black holes resulting in black holes being portals to other universes, according to them we would be living inside a black hole. All speculation if you ask me..

[finsternis]

Yeah, I heard that theory too. But the problem is that you would need something to spit you out on the other side, like a white hole (which is a black hole that spits stuff). But for that you would need some kind of matter that pushes things away instead of in (dark matter?).

[Godfrey I of Leuven]

Or you could ask yourself the question: "Is there another side?"