david_r Posted January 8, 2009 Share Posted January 8, 2009 I finally got around to watching Hubble: The Final Frontier last night. Fantastic program. However I've always struggled with the concept of black holes, and this point of singularity.They cited an example of a black hole where the gravity was that intense that it was ejecting material from its poles (unless I seriously misheard the presenter).So, how does an object with a gravitational force so intense that light itself is consumed, eject material? How does that work then?Confused Dave. Link to comment Share on other sites More sharing options...
acey Posted January 8, 2009 Share Posted January 8, 2009 Black hole jets are caused by magnetic fields accelerating matter around the hole: there's a piece here that descibes them:http://www.space.com/scienceastronomy/080428-mm-black-hole-blazar.htmlPeople mistakenly think of a black hole as "something that nothing can get out of", then wonder how gravity gets out, etc. A black hole, as you say, is a gravitational singularity, which you can think of as a point of infinite density. This leads to consequences around the singularity, such as the event horizon, and also to behaviour outside the event horizon: gravitational, magnetic and electric fields (black holes can theoretically have electric charge).The old name for black holes was "collapsars"; Soviet physicists called them "frozen stars". Those names have their merits too, but become misleading if we take them too literally.Andrew Link to comment Share on other sites More sharing options...
Planet Guy Posted January 9, 2009 Share Posted January 9, 2009 As a black hole sucks in matter, where does the matter that it sucked in go? Does that too collapse in on itself and make the black hole bigger? Link to comment Share on other sites More sharing options...
thing Posted January 9, 2009 Share Posted January 9, 2009 As a black hole sucks in matter, where does the matter that it sucked in go? Does that too collapse in on itself and make the black hole bigger?Yes. Link to comment Share on other sites More sharing options...
thing Posted January 9, 2009 Share Posted January 9, 2009 I finally got around to watching Hubble: The Final Frontier last night. Fantastic program. However I've always struggled with the concept of black holes, and this point of singularity.They cited an example of a black hole where the gravity was that intense that it was ejecting material from its poles (unless I seriously misheard the presenter).So, how does an object with a gravitational force so intense that light itself is consumed, eject material? How does that work then?Confused Dave.As Acey said. The jets come from the accretion disc around the black hole. Link to comment Share on other sites More sharing options...
Talitha Posted January 9, 2009 Share Posted January 9, 2009 Doesn't Hawking Radiation allow certain things to escape from black holes? I'm not into cosmology too much, but I seem to recall reading about this. Link to comment Share on other sites More sharing options...
thing Posted January 9, 2009 Share Posted January 9, 2009 No, it's radiation from the event horizon. It's never been observed but theoretically it could exist. Particles of matter and anti matter are created due to vacuum fluctuations, one flies off into the universe, the other goes into the black hole. Because you have to preserve total energy, the bit that goes into the black hole has negative energy, thus the hole looses mass. However don't hang around waiting for a hole to theoretically evaporate, it would take a lot longer than the universe has been around for this to happen..... Link to comment Share on other sites More sharing options...
astro_dt Posted January 9, 2009 Share Posted January 9, 2009 Dave nailed it in his explanation. I have also had it explained to me (I'm no expert) that as particles in the accretion disk heat up they split in matter/anti-matter pairs, recombine and give off radiation. The effects have been observed indirectly where the jets from the black holes push out the gas and dust in clusters creating voids.CheersDanny Link to comment Share on other sites More sharing options...
acey Posted January 9, 2009 Share Posted January 9, 2009 Dave's explanation is indeed spot on as the "quantum" account of Hawking radiation. The "classical" one is that black holes have entropy, hence a temperature, hence they glow, just like any "warm" object (ie one above absolute zero). This was actually how Hawking first came up with the idea - his realisation of an equivalent quantum viewpoint was his great achievement, as it offered a link between classical and quantum theories of gravity.Jets are a different effect, though, requiring the presence of charged particles around the black hole, and a strong magnetic field to accelerate them.Andrew Link to comment Share on other sites More sharing options...
Talitha Posted January 9, 2009 Share Posted January 9, 2009 Thank you Gentlemen, 'anti-matter' is the term that was in the back of my mind. Just wondering.. does black hole ejecta make up some of the dark matter and/or dark energy that's baffling us? Link to comment Share on other sites More sharing options...
acey Posted January 10, 2009 Share Posted January 10, 2009 No, there are lots of candidates for dark matter/energy but I don't think black holes and their radiation figure in the current list. Link to comment Share on other sites More sharing options...
mjcp Posted January 14, 2009 Share Posted January 14, 2009 The program also eluded to the idea that there was a "bottle neck" of matter as it went over the edge. this may help you visualise it...Think of when you take the plug out of the bath and you have still have bubbles left; As the water drains and you get the whirlpool, some of the bubbles "sit" part way down said whirlpool, and can remain intact for a while (while others drain quickly). I suspect they back up in the bath due to the fact they float, rather then due to quantum interactions though mjcp. Link to comment Share on other sites More sharing options...
vhbelvadi Posted August 6, 2009 Share Posted August 6, 2009 As a black hole sucks in matter, where does the matter that it sucked in go? Does that too collapse in on itself and make the black hole bigger?Yes.No, it's radiation from the event horizon. It's never been observed but theoretically it could exist. Particles of matter and anti matter are created due to vacuum fluctuations, one flies off into the universe, the other goes into the black hole. Because you have to preserve total energy, the bit that goes into the black hole has negative energy, thus the hole looses mass. However don't hang around waiting for a hole to theoretically evaporate, it would take a lot longer than the universe has been around for this to happen.....If the black hole sucks in matter and becomes bigger, how does it evaporate into non-existance? Or, is the rate of evaporation greater than the rate of growth? Link to comment Share on other sites More sharing options...
doat1 Posted August 12, 2009 Share Posted August 12, 2009 Trying to understand black holes will make you go insane, it's like trying to understand the universe. Link to comment Share on other sites More sharing options...
profees Posted August 13, 2009 Share Posted August 13, 2009 From my very limited understanding (comparable to einstein at the age of 4) black holes are unique in as much as the matter/particles etc.. "change" to become something different, something more than even quantum theory etc. can predict. A point of a singularity. I suppose if they have a massive Gravity they also have a massive magnetic field so in theory (i think) the "North" and "south" of a magnetic field could be weaker and change the way the blackhole can contain matter, hence the ejections. Link to comment Share on other sites More sharing options...
blinkity-blonk Posted August 20, 2009 Share Posted August 20, 2009 Where I get confused is when they represent black holes on a plane, which is 2 dimensional. Space is 3 dimensional so it makes no sense.Also worm holes, as I understand them they're black holes without a singularity but a tenuous 'bridge' to a white hole. But they cant possibly work in 3 dimensional space - there's surely nowhere for the hole to go but further into the centre of the dead star or whatever created it. You can view a black hole or worm hole from any direction and you will be sucked in from any direction, leaving no direction but inwards to finally end up having been sucked in.They work on paper, you can fold paper back on itself, but you cant fold an essentially infinite 3 dimensional shape, if you could, which way would you fold it? Link to comment Share on other sites More sharing options...
profees Posted August 20, 2009 Share Posted August 20, 2009 Do you mean they "portray" them as 2 dimensional objects,, i suppose technically the fact that they spin flatterns them out as anything that spins naterally wants to become flattened (spun out).About the paper example use the same example but say instead of paper you are folding water - just accept for this purpose you can fold water. but it would still contain its molecular bonds so it can also be put under presure and would side over its self even under compression. (I may have missed your point though) Link to comment Share on other sites More sharing options...
blinkity-blonk Posted August 20, 2009 Share Posted August 20, 2009 http://upload.wikimedia.org/wikipedia/commons/a/af/Worm3.jpgI wasn't sure I'd got that over exactly how I wanted to. Maybe a picture and some metaphors will help.My point was that space is usually conveyed as a flat 2D grid that you can fold. Its done that way so wormholes are 'easier to understand', and wormholes work on a 2D plane. But in reality space is 3D. If you imagine a wormhole as ball floating in a room, you can see the ball from every angle and if you get sucked into the ball, as you would a wormhole, the only way of getting to another point in the room is to leave the ball the same way as you went in. You can only ever reach the centre of the ball. Any tunnel in a wormhole would have to start and end in the centre of the ball as it cant possibly do anything else which means you would have to bring another point in the room to the centre of the ball as well and then hop across. but how do you distort a 3D shape like that without totally destroying it? Link to comment Share on other sites More sharing options...
vhbelvadi Posted August 22, 2009 Share Posted August 22, 2009 Interesting question there, blinkity-blonk.I'd like to know the answer too.Could it mean that the whole white hole theory is wrong, and that we will end up simply at the centre of the black hole (whatever that means).Or does it mean that the 2D grid-plane of space (or at least as space is represented) is merely one of infinite repeatedly similar planes forming layers, and a wormhole opens, not into the opposite, folded face of the same plane, but into a completely new plane, bypassing infinite number of other planes on the way? Something like a room with numerous layers (if I may call them) of curtains hanging from a flat roof, such that each curtain is in contact with the one immediately next to it. So, if you push one curtain, you distort many others, and if you find a hole which opens, say, at the curtain you are currently in, and leads to the 47th curtain from there, you'll travel through this 'wormhole' to the 47th curtain and go about distorting all others with which the 47th one is in contact; and, in general, the whole set of these curtains forms a 3D space.I hope I've made my idea clear. Link to comment Share on other sites More sharing options...
Karo Posted August 22, 2009 Share Posted August 22, 2009 http://upload.wikimedia.org/wikipedia/commons/a/af/Worm3.jpgI wasn't sure I'd got that over exactly how I wanted to. Maybe a picture and some metaphors will help.My point was that space is usually conveyed as a flat 2D grid that you can fold. Its done that way so wormholes are 'easier to understand', and wormholes work on a 2D plane. But in reality space is 3D. If you imagine a wormhole as ball floating in a room, you can see the ball from every angle and if you get sucked into the ball, as you would a wormhole, the only way of getting to another point in the room is to leave the ball the same way as you went in. You can only ever reach the centre of the ball. Any tunnel in a wormhole would have to start and end in the centre of the ball as it cant possibly do anything else which means you would have to bring another point in the room to the centre of the ball as well and then hop across. but how do you distort a 3D shape like that without totally destroying it?In the same way you folded the two dimensional sheet through the third dimension, you would fold the three dimensional space through the fourth dimension. You would pick two points to be the ends of your wormhole, and bend them through the fourth dimension until they touched.A simpler example would be to consider rolling a sheet of paper so that the two opposite ends of the sheet touch - to any hypothetical 2d-being on the surface of that paper, it is now infinitely long, or they can instantly travel to the opposite end of the sheet by walking off the top. If they walk along it, when they step across the join they're wormholed back to the other end! As they have no concept of "up" - the third dimension - they aren't aware of the fold through it, just as we would not be if if was a 4th dimensional fold -- you would enter this space and instantly be somewhere else, although the distance back to the other end of the wormhole is minimal. Link to comment Share on other sites More sharing options...
Tantalus Posted August 22, 2009 Share Posted August 22, 2009 ...A simpler example would be to consider rolling a sheet of paper so that the two opposite ends of the sheet touch - to any hypothetical 2d-being on the surface of that paper, it is now infinitely long, or they can instantly travel to the opposite end of the sheet by walking off the top... Surely a piece of paper is three dimensional - it has thickness as well. Link to comment Share on other sites More sharing options...
lulu Posted August 23, 2009 Share Posted August 23, 2009 I think of of the problems we have with how to portray "space" or "black holes" is that we always try to think of things in 3D terms, or 2D terms whereas we should really be thinking about space-time i.e. a 4D term. Black holes are so massive that it is space-time which gets distorted, not just space. Its just like when we talk about open or closed universes and portray them as "saddle shaped" object or "spheres" etc. I guess we really can't visualize a 4D space-time so to simplify things we represent them in a 2-D or 3-D way so we can at least see something "bending" or "curving". Link to comment Share on other sites More sharing options...
Karo Posted August 23, 2009 Share Posted August 23, 2009 Surely a piece of paper is three dimensional - it has thickness as well. Thats true but you're only really considering the surface of the paper in the example. Paper just serves as a suitable prop because it is very thin -- not zero thickness, of course, so you have to 'pretend' it's flat.I guess we really can't visualize a 4D space-time so to simplify things we represent them in a 2-D or 3-D way so we can at least see something "bending" or "curving".That's exactly it.. to demonstrate gravity's effect on spacetime for example, the famous ball-on-a-rubber-sheet demonstration puts the 4D phenomenon into simple 3D terms. You have X and Y position on the sheet representing space, and the Z (up/down) direction is used to represent the distortion of spacetime caused by gravity/mass. Of course with a real object, the effect on spacetime happens in 4 dimensions, so space and time are deformed around the mass in all directions - you have 4 things you want to show but only 3 dimensions - you have to simplify somewhere hence the "pretend this paper is space" Link to comment Share on other sites More sharing options...
blinkity-blonk Posted August 23, 2009 Share Posted August 23, 2009 There's some good stuff there that I'd not thought of, like vhbelvadi's idea of curtains. There's a video on the internets called 'imagining the 10th dimension' I think - I can follow it up to where he says fold through the 4th dimension, I simply cant visualise how that's done. Also I thought now scientists were saying time wasn't the 4th dimension (though I may have misheard that) Link to comment Share on other sites More sharing options...
vhbelvadi Posted August 24, 2009 Share Posted August 24, 2009 There's some good stuff there that I'd not thought of, like vhbelvadi's idea of curtains. There's a video on the internets called 'imagining the 10th dimension' I think - I can follow it up to where he says fold through the 4th dimension, I simply cant visualise how that's done. Also I thought now scientists were saying time wasn't the 4th dimension (though I may have misheard that)Could you please post the link to the video, Blinkity-blonk?And, about the 'time-is-not-4th-dimension' discussion, where did you come across that? Link to comment Share on other sites More sharing options...
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