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Some guy (UK)
13-09-2005, 17:00
Right so after reading some thread here on warseer about how the sun has 4-5 billion years left. It got me wondering about the ever mysterious black holes holes that are formed by some stars when they die (apparently, but not the same type of stars as our sun btw). adn i was wondering- how much does what is said about black holes sound similar to the good 'ol warp??

I mean ive read all sorts off fluff of how you can be sent to anywhere in the universe by way of warp travel, get sent back in time or forward (this is the what the fluff said btw but i rekon its true) and all sorts off other things i mean all those dissapearing ships must go somewhere!!!

Now i have watched a few programs about space, one or two of them were about black holes. Now on that show, horizon i believe, the experts were saying how that no one really knows what is happens when one enters a black hole, e.g sent into another dimension, go back in time, pop out somewhere in this galaxy or another one for that matter- who knows???

Also there is also substantial evidence of a black hole in the centre of the milky way (arrrhhhh run for the hills :D !!!)

here is what i came up with to back up my point, as you see its only a theory.

'Most astronomers believe that galaxies like the Milky Way were formed from a large cloud of gas which collapsed and broke up into individual stars. We now see the stars packed together most tightly in the centre, or nucleus. It is possible that at the very centre there was too much matter to form an ordinary star, or that the stars which did form were so close to each other that they coalesced to form a black hole. It is therefore argued that really massive black holes, equivalent to a hundred million stars like the Sun, could exist at the centre of some galaxies. '

website- http://csep10.phys.utk.edu/guidry/violence/black6.html- point number 2 btw.


So this thread has two points-

1) how blacks holes seem partly familiar to the warp in 40k (maybe they were insipred by black holes- you tell me)!: write 'warp' at the start of yur post/ relevant paragraph

2) what you think about black holes: write 'black holes' at the start of your post/ relevant paragraph

anyway,

C ya, Some Guy (UK)

The pestilent 1
13-09-2005, 18:41
i love how black holes say "nu-uh!" to the laws of thermodynamics.
the bigger it is, the lower its tempereture.
so cool :)
thats the best bit anyway, all that stuff on gravity fields and the threshhold of the event horizen and whatnot was interesting but not "breaking thundamental laws of physics" interesting.

Tormentor of Slaanesh
13-09-2005, 18:50
there's one in our galaxy right now that "may" kill us all. there's also an asteroid thats gona hit earth in 2o years time...

Wez
13-09-2005, 19:25
there's one in our galaxy right now that "may" kill us all. there's also an asteroid thats gona hit earth in 2o years time...
...and there's also scare mongering by newspapers to sell copies.;)

-Wez

Asher
13-09-2005, 19:30
there's one in our galaxy right now that "may" kill us all. there's also an asteroid thats gona hit earth in 2o years time...

The one they named Apophis? It will pass the earth close by (in galactical measurements) but not hit it. The distance will be twice the moon distance if I remember correctly.

One known black hole is in the middle of our galaxy. A real monster it seems as it has a some million masses of the sun.
There are some other around but they are all to far away to be a threat.

Crazy Harborc
13-09-2005, 19:50
Then, there's the bit about all that we can "see(by any means)" is but a micro dot on the smallest head of a pin.

New Cult King
14-09-2005, 00:57
Nobody could pass through a black hole, as they are so dense, any matter would be reduced to its constituent atoms by the hole's gravity.

They do present an interesting phenomena though... proving that for all the things we do 'know' about the universe, there are so many more we don't.

He Who Laughs
14-09-2005, 01:05
Getting close to a blackhole is not a good idea. Due to the incredibly high gravitional force gradient, the gravity pull gets stronger with each millimetre you get closer - so at some point, (say you were going feet first) the gravitational force acting on your head would be say 10 m/s2, whilst the force at your feet would be 100m/s2....

And the result of this?
Well, the scientists have a name for this phenomenon - spaghettification :evilgrin:

Bmaxwell
14-09-2005, 01:19
gotta love some of the new scientictf terms

Kordos
14-09-2005, 01:33
Black Holes

Hawking recently revised his view on black holes, first he said nothing can escape from them but then sometime last year he changed that opinion and decided some things DO escape from black holes.

What I really love about black holes is that we don't even know that they exist (i found this out when researching an astronomy report on super massive black holes) - here on earth we've come with some lovely theories about these things which form after large suns die, we've even made some nice mathematics to back it up – then we look towards the heavens and lo and behold we find some clues to indicate that these things we call black holes are there – though they may not exist at all and actually be something utterly alien and bizarre that is giving us these ‘clues’

Also another interesting thing – the mathematics governing ‘black holes’ is completely reversible, so you can, in theory have a ‘white’ hole

:0)
14-09-2005, 02:13
i love how black holes say "nu-uh!" to the laws of thermodynamics.
You put things so eloquently sometimes. That make me laugh, thank you. :)

Jaq Draco
14-09-2005, 02:47
well since we are still a bit unaware of the complete science of black holes, im pretty sure the stuff about them having intense gravitional pulls, is about right.

if so then im thinking, there is no way, they can be utilised for any means whatsoever.

just basically big cosmic vacuum cleaners they be

New Cult King
14-09-2005, 08:53
Also another interesting thing – the mathematics governing ‘black holes’ is completely reversible, so you can, in theory have a ‘white’ hole

Which are considered by some to be the other end (or exit region) of black holes...

The whole thing intrigues me, but it's ultimately all supposition. There are things here on Earth more worthy of the time and energy being spent looking beyond the furtherst reaches of our solar system, when we can't even reliably get ourselves safely into space and back...

santiholgado
14-09-2005, 08:58
Black holes

Nobody has ever been near one, experiment with one or whatever...

... so anything you can say about them is just a theory ...

... but everyone, and mostly journalists, present it always as established facts

blacksmith
14-09-2005, 09:40
The way I always thought of black 'holes' were not as holes but as unimaginably dence but increadibly small centres of mass. As gravity is the force of attraction between all objects with mass and is always an attractive force, the large mass of the black hole can suck in other massive objects.

When said massive object gets so close, the force of gravity exerted on all of the parts making up its atoms (all the fundamental particles that make up matter) is enough to collapse the atom, thus adding to the mass of the black hole but not increacing its size significantly. (most of an atom is empty space, so a lot of them could be added to the black hole and not make irt much larger)

The strength of the gravity that a black hole can exert on other particles is even enough to draw photons of light towards it. If light cannont escape its gravitational pull, it will appear black in colour.

As for the idea of white holes... the force of gravity is an accelerating force (someone mentioned how your head would be going 1mm/s and your feet would be doing 100mm/s). As you get closer to the black hole, the force accelerating you would increace, therefore your speed would increace.

It may just be possible that for some masses this gravity could cause the mass to go into a small orbit around the black hole (like our moon around earth) before centrepetal forces could in a way fire it outwards again back into outer space. If mass could be ejected, so too would light photons be able to be ejected, thus a white hole would be possible.

Well, at least thats what I think. :rolleyes:

Wiseman
14-09-2005, 09:59
Well, the scientists have a name for this phenomenon - spaghettification
it sounds oh so scientific doesnt it, if i didnt know it already i would struggle to believe that it is a scientific term :p

Scythe
14-09-2005, 10:01
well since we are still a bit unaware of the complete science of black holes, im pretty sure the stuff about them having intense gravitional pulls, is about right.

if so then im thinking, there is no way, they can be utilised for any means whatsoever.

just basically big cosmic vacuum cleaners they be

Well, they can be used as clean dumpyards to put your dozens of trash instead of polluting some planet with it...;)


As for the idea of white holes... the force of gravity is an accelerating force (someone mentioned how your head would be going 1mm/s and your feet would be doing 100mm/s). As you get closer to the black hole, the force accelerating you would increace, therefore your speed would increace.

It may just be possible that for some masses this gravity could cause the mass to go into a small orbit around the black hole (like our moon around earth) before centrepetal forces could in a way fire it outwards again back into outer space. If mass could be ejected, so too would light photons be able to be ejected, thus a white hole would be possible.


Buth would a white hole be the total opposite of a black hole? If so, it should push you away from it, instead of drawing you towarths it. Is that even possible (negative gravity)? And how would something like that come into excistance? And since it pushes everything away from it, wouldn't it cancel itself by doing so?

Wiseman
14-09-2005, 10:24
yeh id think that a white hole would tear itself apart as it tried to push itself away from itself

DarkSoldier
14-09-2005, 10:54
The black hole at the centre of the galaxy is called Sagittarius A*; its mass is estimated to be 2x10^36 kg, or a million solar masses, contained in a volume of space about 240 AU (36x10^9 km) across. It's 10 degrees west from the centre of the constellation Sagittarius, toward Scorpio.


Nobody has ever been near one, experiment with one or whatever...

... so anything you can say about them is just a theory ...We haven't got close to the Sun or experimented with it, but do you doubt that it's a massive fusion furnace pumping out 383x10^24 watts of power every second?

To understand black holes requires understanding of general relativity, astrophysics, and quantum physics beyond most people's ken. I feel that I can trust the reports of physicists like Stephen Hawking.

Asher
14-09-2005, 11:20
Buth would a white hole be the total opposite of a black hole? If so, it should push you away from it, instead of drawing you towarths it. Is that even possible (negative gravity)? And how would something like that come into excistance? And since it pushes everything away from it, wouldn't it cancel itself by doing so?

Quite a lot of scientists belive that about 70% - 90% of the universe consists of so called 'dark energy' which is the opposite of gravitation. The concept of dark energy is used to explane some phenomenons yet not rationalisable by gravitation and matter alone. For example why did the expansion of the universe accelarate instead of stay in same speed (which would be the normal phyical conclusion).
Note that there is no evidence of such energy yet. Pure speculation.

I can't really imagine an oppoiste black hole (to be honest a black hole is hard to imagine) as that thing would need to have a infinite repulsion effect (anlog to the infinite gravitation in a black hole).


if so then im thinking, there is no way, they can be utilised for any means whatsoever.

They could be used to gain energy. The black hole itself is invisible but it gets visible once eiher it passes in front of bright object, bending their light or while feeding on stars. In the latter proces a lot of the energy is thrown out again in an highly engery dense pillar. Some of them can get lightyears long, emitting energy in form of gamma rays.
The big mommas of this pillars are the so called gamma bursts or flashes. When a suppermassive star dies in its place of birth (note: lightyears of space full of gas) a pillar of gamma rays is spittet out for a few seconds. The energy thrown out is the same a whole galaxy (!) produces in that time. This phenomenon that was detected in '73 and is known as a Hypernova (no kidding).
The amount of energy harvested there would be enough for a eternety.


Black holes

Nobody has ever been near one, experiment with one or whatever...

... so anything you can say about them is just a theory ...

True, but there is a lot knowlidge gained from observing black holes in different periods of their existence. The most infromation about them was gained by observing the behavior of objects crossing their path (like suns).
The whole subject has a bit of exageration or misunderstanding in it when it hits the media and masses. Especally the shape of the thing which is not a hole but a round object (the gamma ray pillars escape on both sides vertically to the sun spinnig around the black hole). To understand it as a whole a lot of sophisticated physical knowlige is needed.

Black hole are however not the only interessting thing out there. Neutron stars and the birth of stars are some of the most interessting things (and thus worth the money). Aparently we all are made of stardust. ;)

de Selby
14-09-2005, 11:37
The element Helium (for example) was discovered off-earth using the 'new' science of spectroscopy. Only later did we identify it here on earth. So just because you can't touch it doesn't mean it isn't real, maybe one day we'll be manufacturing little black holes in the lab (harmless; they evaporate).

Somebody mentioned white holes; a WH is a mathematical solution to the equations of general relativity (the well-tested equations that predict/describe black holes). The fact that the WH mathematical solution exists, suggested to some scientists that they might physically occur under some circumstances, possibly popping into existence like mirror images of black holes. However this idea now seems unfashionable. The closest thing to a WH that gets (semi-seriously) discussed these days is the end of a 'wormhole'; that is, a bridge of distorted space-time connecting too otherwise distant points. One end of the wormhole would look a bit like a BH, the other end a bit like a WH. To connect and stabilise the two ends requires a couple of hypothetical physical properties and processes that have never been observed in the real world.

And I wouldn't say that BHs 'break' any known laws of Physics. It's just a bit of a challenge reconciling the two sometimes, particularly wrt Information theory. It's the entropy, rather than the temp, which causes most headaches.

santiholgado
14-09-2005, 15:46
True, but there is a lot knowlidge gained from observing black holes in different periods of their existence. The most infromation about them was gained by observing the behavior of objects crossing their path (like suns).
Having more observations gives a better theory, but it's still a theory, not a fact. If you've studied physics at school, remember the different theories of the atom. First we had the electron running in circular orbits around the nuke, then we had him with elliptical orbits instead and finally we end with quantum physics where you don't know where the electron is. They were all theories based on different suppositions, experiments and a bit of imagination, but at the end, they were wrong (at least the first two). In both cases, they didn't have the fact about the electron, just theories.

That's what I mean about the black holes theory: they're just theories, and it's alright if you leave it that way, but there's lot of people (journalists specially) that present them as "the truth". Maybe, in the end, one of those theories ends being the truth, but today, regarding black holes, they still aren't.


We haven't got close to the Sun or experimented with it, but do you doubt that it's a massive fusion furnace pumping out 383x10^24 watts of power every second?

Yes, I doubt it! :D Nobody has measured that power there, so it's just a theorical calculation. It can be absolutely right, very approximated or completely wrong, depending on how many of the data used is right, because that calculation has some theorical components in it.

Xisor
14-09-2005, 16:05
Interstingly enough, my advisor at University(a certain Ulf Leonhardt of St Andrews) done a bit proposing the possibility of 'Optical Black Holes', using a rotating super-cooled fluid to artifically slow down light and *mimic* the gravitational effects using mechanical methods. In this way, a fluid could be set to rotation so that it'd totally absorb certain light bands, thus becoming as 'black' as a black hole, I believe. In this way they hope to be able to examine and experiment with Hawking Radition, the halfs of partical pairs that are created on the Event Horizons. This'd be possible since the rotating fluid would have it's own event horizon. Ingenius eh?

All the quirks and marvels(optically speaking) of Black Holes, but none of the gravitational side effects. Handy!

Edit: You can see a list of the various articles concerning this here: Linky (http://www.google.co.uk/search?hl=en&q=ulf+leonhardt+optical+black+holes&meta=)

Xisor

The pestilent 1
14-09-2005, 16:14
You put things so eloquently sometimes. That make me laugh, thank you. :)

*bows* i couldnt remember the actual term, rather typicly.
that, and i had just passed that bit in Stephen (or is it Steven?) hawkings "A Brief History Of Time"

Anyway, i always liked the theory that matter/energy that is pulled into a blackhole (and doesnt come out again, i some stuff about Charges that i dont really remember, distractions while i read it and all) is theorised to be dumped off in Alternate realities, so in theory, for each black-hole there is a succesful universe.
always liked that idea, even if there is no life in our universe (or rather intelligable life) then we have a myriad of others.
comforting somehow.

t-tauri
14-09-2005, 16:26
Having more observations gives a better theory, but it's still a theory, not a fact. If you've studied physics at school, remember the different theories of the atom. First we had the electron running in circular orbits around the nuke, then we had him with elliptical orbits instead and finally we end with quantum physics where you don't know where the electron is. They were all theories based on different suppositions, experiments and a bit of imagination, but at the end, they were wrong (at least the first two). In both cases, they didn't have the fact about the electron, just theories.

"Just a theory" as a way to dismiss science is a line run out by people who don't know what a theory is. What you're talking about there are models, ways to explain and predict behaviour. The Bohr Rutherford atomic model is a perfectly adequate way to explain most of the science of chemistry and make predictions of chemical properties and reactions. They had plenty of facts about the electron, enough to make TVs, radios and computers.

A scientific theory is a way to explain things which hasn't been proved wrong yet, and has passed all possible tests. The standard model at the basis of Quantum Mechanics is "just" a theory, but it still explains most of subatomic physics although latest evidence may suggest it is wrong, at least in some respects. That's what theories are for to examine and modify.

White holes probably don't exist, simply because they'd be so easy for current telescope/sensing technology to detect. The thing to remember about Black Holes is we don't properly understand how gravity works- I know more about the forces holding my atoms together than about the force holding me to the earth. Until we make a leap in the understanding of gravity analogous to Newton's Law of Gravitation then we'll remain fairly ignorant and speculative as regards to Black Holes.

TheSonOfAbbadon
14-09-2005, 16:54
i love how black holes say "nu-uh!" to the laws of thermodynamics.
the bigger it is, the lower its tempereture.
so cool :)
thats the best bit anyway, all that stuff on gravity fields and the threshhold of the event horizen and whatnot was interesting but not "breaking thundamental laws of physics" interesting.

Maybe the bigger it is the more energy/mass [mass is energy, according to Einstein, and alot of other respectable people] it sucks in, therefore the less thermal energy is lost.

On touching a black hole, you're *********. No really, ********* like you've never known. You're instantly sucked in and become part of the super-dense mass of the orb that not even light can escape from.

What else would happen? You don't really think that a black hole could send you to an alternate universe, do you?

The pestilent 1
14-09-2005, 17:03
well in theory you wouldnt know that your buggered, until you died.
by which point it is ofcourse too late :p


Maybe the bigger it is the more energy/mass [mass is energy, according to Einstein, and alot of other respectable people] it sucks in, therefore the less thermal energy is lost.
i think that is the general concensus yes, gicen that its gravity is Absolute (IE: nothing can escape, matter, energy, light time, the lot is sucked in. except those things that arent (posotive charge or somthing, dont remember i was being distracted as i read that so havent absorbed it, somthing to redo while bored tommorow i reckon)
so heat (being a form of energy) is probably absorbed.
but then, surely it would all be absorbed, as a black-holes mass only dictates its gravity-well and area of influence :eyebrows:
thus is my understanding anyway.

TheSonOfAbbadon
14-09-2005, 17:09
Time? Why would time be sucked in? Time is just the passing of one event to another, it has no actual mass.

The pestilent 1
14-09-2005, 17:16
Time slows as you approach a black-hole.
thats the theory anyway, cant be proven ofcourse.

eg: one guy is sucked into the hole, but is unaware of this.
a person watching would see him being sucked in (until the point of no return anyway) but would see an obvious slowing of time.
time being defined by our perception, ofcourse our perception is based upon other tangible effects (light and sound primarily) so in effect time isnt being slowed, just our perception.

its all a load of BS really, but hey its easier than saying "matter, energy, light and our perception of four dimensional time)

Terminatorphoenix
14-09-2005, 17:27
actually we may be able to see white holes,really how many stars in the sky are really stars i mean a couple of centuries ago we thought the stars were angels before then gods before then who knows

Crazy Harborc
14-09-2005, 23:25
What is the latest theory on what is on the "other side" of a black hole??

Kordos
14-09-2005, 23:39
nothing, black holes are not 'holes' they contain highly compressed matter

Crazy Harborc
15-09-2005, 00:29
That is still the "theory"?? Um.........we know this how?? :angel:

Kordos
15-09-2005, 00:39
well yeah it's all theory and we 'know' this cause that is what the theory says

Asher
15-09-2005, 09:36
That is still the "theory"?? Um.........we know this how?? :angel:

The shape? I mentoned this a bit earlier. (Not that anyone really reads my posts) While feeding on a star the black hole is localisable. Because there are two plasma jets verically on each side to the accreaton disk (which itself is rotating) thus we can assume that it in fact is a spiral object rather than a hole. (both the plasmajet and the disk are measurable as they emmit radiaton).

Artistic Visualisation (http://upload.wikimedia.org/wikipedia/en/thumb/2/2a/Accretion_disk.jpg/750px-Accretion_disk.jpg)

Scythe
15-09-2005, 10:26
actually we may be able to see white holes,really how many stars in the sky are really stars i mean a couple of centuries ago we thought the stars were angels before then gods before then who knows

But again, if white holes really excisted, they wouldn't be able to remain. If, like Asher said before, there excists something like negative gravity (or black mather, wathever you call it) which pushes mather away from it, it would never be able to clot together to form a white hole in the first place. Even if one was formed, the mather would just push itself apart, as each element pushes itself away from other elements. So I don't think they can excist.

And the term 'white hole' is also quite wrong. It isn't a hole that draws you towarths it, it's something that pushes you away from it.

Jaq Draco
15-09-2005, 13:54
even though we dont know much about black holes

i find the concept of white holes implausible

Kordos
15-09-2005, 13:59
even though we dont know much about black holes

i find the concept of white holes implausible


'white hole' is just a term for the opposite of the black hole (when you reverse the mathmatics) there is no evidence that they exist

Jaq Draco
15-09-2005, 14:01
that much im aware of, but are you sure there is the concept of balance

i.e. if there is a black hole, the opposite should be a white hole.

the very fact we exist, proves there is no balance, since there is more matter than anti-matter

Sojourner
15-09-2005, 14:07
In much the same way as you can reverse signs in the relativistic energy equation and get a particle with negative mass and/or a speed greater than that of light, a tachyon. They've never been observed but there are some serious efforts going on to try and find them.

Kordos
15-09-2005, 14:17
that much im aware of, but are you sure there is the concept of balance

i.e. if there is a black hole, the opposite should be a white hole.


everything is conserved, momentum, heat, light, etc etc there is always balance - you use the term opposite - and you are thinking the wrong thing - balance does not mean opposite - black holes achieve their balance by turning everything they 'suck' into energy and evaporate into space - there is not necessarily a ‘white hole’ to balance it out – I am merely pointing out that since the black hole theory also predicts ‘white holes’ (which I agree seem implausible) then perhaps there is something wrong with the theory (as a good theory shouldn't predict something that cannot exist)



the very fact we exist, proves there is no balance, since there is more matter than anti-matter

umm faulty logic - that is more philosophical than science and matter and anti matter are thought to exist in equal amounts which suggests balance

Sojourner
15-09-2005, 14:18
matter and anti matter are thought to exist in equal amounts which suggests balance

By whom? Much of modern cosmology is trying to figure out why matter and antimatter are not balanced.

Jaq Draco
15-09-2005, 14:22
sorry if i seem un-educated, it was what i read, the text i read it from, must have been inaccurate, sorry guys

Kordos
15-09-2005, 14:25
It really depends on which physicist you talk to, the major problem is that anti matter is so hard to detect.
I was flipping through a some physics notes a friend of mine lent to me (this is university physics, not high school) and they were talking about huge masses of antimatter existing around the universe (all this ‘dark matter’ stuff) which would account for some of the interesting light shows we can observe happening around quasars and the like

Sojourner
15-09-2005, 14:28
Incidentally, just in case anyone wasn't sure:

Antimatter and antigravitation are not the same thing. Antimatter still behaves like normal matter in a gravity well, in much the same way that both matter and antimatter still emit the same kind of photons.

As for white holes: it isn't so outlandish if you think beyond three euclidean dimensions. I don't know many specifics about black holes but as I understand it, they're a distortion in spacetime. The way you guys are describing these sorts of anomalies, you imply that black holes go 'down' like the grid diagrams you see in books, while perhaps white holes go 'up'. Even though this would make sense in the context of a 2-D diagram, in a physical sense, it is nonsense. Essentially both gravitating particles and antigravitating particles would produce the same kind of dent in spacetime - you can't distort 'outwards' as there's no priveliged direction for it to go 'out' into.

Kordos
15-09-2005, 14:28
sorry if i seem un-educated, it was what i read, the text i read it from, must have been inaccurate, sorry guys

its ok, most physicists can't agree on a time of day, keep on reading, pick up university physics text books, try and read some of hawkings stuff (i say try because it gets pretty hard to read sometimes) alot of stuff will contradict each other - read and form your own opinion - I may not actually be right after all

Scythe
16-09-2005, 09:25
umm faulty logic - that is more philosophical than science and matter and anti matter are thought to exist in equal amounts which suggests balance

Equal amounts of matter and anti-matter would just cancel each other out. There's a lot matter in this universe, and hardly any anti-matter, which suggests that there was more matter in the first place, and probably cancelled out most of the anti-matter. Wouldn't large amounts of anti-matter draw large amounts of matter to them anyway, cancelling each other (since both are subject to gravity)?


As for white holes: it isn't so outlandish if you think beyond three euclidean dimensions. I don't know many specifics about black holes but as I understand it, they're a distortion in spacetime. The way you guys are describing these sorts of anomalies, you imply that black holes go 'down' like the grid diagrams you see in books, while perhaps white holes go 'up'. Even though this would make sense in the context of a 2-D diagram, in a physical sense, it is nonsense. Essentially both gravitating particles and antigravitating particles would produce the same kind of dent in spacetime - you can't distort 'outwards' as there's no priveliged direction for it to go 'out' into.

I still can't see how a white hole would hold together... or put otherwise... in what aspects would a white hole differ from a black hole in the first place then?

Sojourner
16-09-2005, 09:29
This is all educated conjecture rather than scientific hypothesis, so I really can't say. There's no observed phenomena which suggest such a gravity field is even possible.

Str10_hurts
16-09-2005, 11:26
Ok just a side question, the black hole sucks in matter light ect. wil this procces go on for ever or wil it stop at some point being full?

What will happen then? it dies? or a bang?....could a black hole lead to the 'big' bang?

Sojourner
16-09-2005, 11:31
Don't know the answer to that one. Prof. Hawking believes that black holes will eventually evaporate by emitting radiation, but whether this applies when they're still drawing in material is anyone's guess.

de Selby
16-09-2005, 12:06
There was a good program on BBC2 last night dealing with some of these questions, for those in the UK. Anyone else see it?

Back on White Holes: Sojourner is right to say that it's a bad idea to think in terms of black holes bending space 'down' and white holes stretching it 'up'. Visualization tools like this can lead you astray.

The basic BH mathematics describes the spacetime around a concentration of collapsed matter. You can think of this as a coordinate system, with every point in the spacetime around the hole being represented within the coordinates, and each point in spacetime having defined properties (like; gravitational field strength).

Oddly, only half of the coordinates in the system are required to describe all of the spacetime around the BH. The other half may be redundant (this seems likely) but if they describe anything physical it would be a WH; a region of spacetime which matter can exit, but not enter.


Antimatter, as said before, gravitates normally. It's something of a puzzle why the physical properties of matter and anti-matter are almost-but-not-quite symmetric, and how exactly this has led to our nearly-all-matter visible universe.


edit: forgot something. Yes, all holes will eventually evaporate, at arate inversely proportional to their mass. They get bigger all the time there is more material to draw in, but evaporation is inevitable. However, this is one of the slowest processes in the universe. The distant furure of our universe apparently involves heat death and evaporating black holes for some 10^100 years or something (I actually can't remember the exact timescale, but it is truly vast compared to anything we know).

Jaq Draco
16-09-2005, 13:23
Didnt Hawking postulate that the 'stuff'(for want of a better term) evaporating out of black holes are called Hawking Radiation. if im right

then what exactly is Hawking Radiation

Sojourner
16-09-2005, 13:47
There is a process where black holes emit radiation by zero-point production of photon pairs either side of the schwarzschild radius. One photon flies off into space and the other is drawn into the hole. Basically, matched pairs of particles pop in and out of existence all the time, and black holes simply seperate them before they can collide and vanish. This is one kind of radiation.

whether Hawking radiation is the same thing, I'm not sure. I can't see how this would lead to black hole evaporation but at the same time, I can't think of any other way for them to emit radiation.

Jaq Draco
16-09-2005, 13:50
wouldnt black hole evaporation imply the removal of the mass contained in the singularity though, sounds like the black hole is creating particles instead of having them evaporate off of the singularity

de Selby
16-09-2005, 14:44
Simplest thing is to say: by conervation of mass, anything emitted from the horizon has to be knocked off the mass of the whole hole. I think you could also make an argument based on conservation of mass-energy, taking into account the gravitational binding energy of the whole, whereby the mass-energy of the hole is reduced by Hawking radiation, but this is beyond my ability.

Certainly Hawking radiation is the accepted mechanism by which holes evaporate, so the TP community is happy with it. Equally certainly the paricles emitted are not the particles that fell in. Exactly what happens to these particles (or rather the information by which they are identified) is an outstanding mystery

Scythe
16-09-2005, 14:44
I'm no expert on this as well, but I believe it had something to do with that the particles have to draw their mass/energy from somewhere when they 'appear', which is in this case the black hole. When one particle is emmited, and the other sucked back in the black hole, the hole essentially loses the mass/energy of the particle emmited. But as far as I know this is all very theoretical still.

edit: damn, beat me to it... :D

Kordos
16-09-2005, 15:11
Throughout the universe, pairs of virtual particles (particles and their antiparticles) appear and dissapear so quickly that they do not violate any laws of physics. The tidal force just outside the event horizon of a black hole is so stron that it can tear these two particles apart before they destroy each other. The gravitational energy which goes into this makes them real, and therefore permenant. Because the black hole's gravitational energy is used it loses some of its mass - this is the Hawking Process

de Selby
17-09-2005, 11:56
Interesting black hole link here:

giant black hole without a galaxy to call home. (http://www.eso.org/outreach/press-rel/pr-2005/pr-23-05.html)

Jaq Draco
18-09-2005, 00:21
indeed tis very interesting

so how exactly do we detect blackholes??

its obviously not through visual identification of the accretion disk

TenTailedCat
18-09-2005, 00:59
You detect them by watching the crap going into them, don't you?

Kordos
18-09-2005, 05:54
indeed tis very interesting

so how exactly do we detect blackholes??

its obviously not through visual identification of the accretion disk

at the moment we can only detect black holes in binary star systems - they draw gas from the star toward the black hole, the gas spirals around getting denser and denser forming an accretion disc - the compression is so great that the gas emits x-rays - we can observe these x-rays being given off and also the huge gravitational pull of the black hole is enough to make the star 'wobble'

so far the major candidate for a black hole is Cygnus X-1 (a binary star system) based on the 'wobble' and measured x-rays given off - but it depends on who you talk to, my astronomy lecturer was dead certain that there is a black hole there while my physics lecturer would say “well it fits the math” and refuse to elaborate on the subject

Jaq Draco
19-09-2005, 14:28
i wonder what it'd be like actually seeing one

Sojourner
19-09-2005, 14:38
Generally black holes are powerful x-ray emitters, particularly ones close to stars, because the charged matter orbiting them is accelerated as it's pulled in.

de Selby
19-09-2005, 18:38
In the absence of material falling into the hole, it would just look like a black sphere (or ellipsoid if rotating). You could also expect to see gravitational lensing (and poss red/blueshifting) of anything (stars) in the background.

Interestingly, the really big holes inside quasars and galaxies are so huge that apparently the tidal forces at the event horizon are quite survivable. So you could jump in and have a chance to look at the outside world from inside the hole before the inevitable spaghettification occured.

Jaq Draco
19-09-2005, 22:54
wait a min de Selby, why is it that because the big big ones have survivable tidal forces at the event horizon. doesnt seem to sound right

i would have the bigger the badder it'd be

Kordos
20-09-2005, 00:14
wait a min de Selby, why is it that because the big big ones have survivable tidal forces at the event horizon. doesnt seem to sound right

i would have the bigger the badder it'd be

nope, the bigger the black hole the simplier it is - also it is easier to make a suppermassive black hole than a 'normal' blach hole

Jaq Draco
20-09-2005, 01:04
@kordos: doesnt really explain things,

my thinking being, the bigger the black hole, the greater the gravitational forces,

Kordos
20-09-2005, 05:08
@kordos: doesnt really explain things,

my thinking being, the bigger the black hole, the greater the gravitational forces,

sorry was posting with a big hangover, what i was trying to say is that it isn't really the bigger - the badder, a supermassive black hole is just simply bigger

de Selby
20-09-2005, 11:02
The explanation is that the 'point of no return'; the event horizon, is defined to be the radius from which nothing, not even light, can escape. The more massive the hole, the bigger it is (the radius is actually directly proportional to the mass, interestingly), but the actual strength of the field is always the same at a black hole horizon, by definition, and then rises to infinity inside.

The second thing to realize is that it's not actually the strength of the field (as such) that would kill you. Provided you were in free-fall, you would feel weightless all the way in (just as when falling here on earth). What would stretch you apart is the tidal force; the difference in gravitational force on your feet and your head would quickly exceed the tensile strength of the human body and tear you apart. For a small hole, this difference (across six feet of human body) would be large at the event horizon. For a big hole the tidal force across the human body would be small even at the event horizon, because everything is on a bigger scale relative to you, the human.

Everything then goes inevitably to infinity once inside, so then: kaput.

Jaq Draco
20-09-2005, 13:04
ahh im following you now, a small event horizon means the difference in tidal forces accross a distance ie your example is greater than the bigger event horizon,

now i get it

although in any case, you go near one, your screwed