Invoking The Voyagers Against Id |
Invoking The Voyagers Against Id |
Oct 24 2005, 03:04 PM
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Cornell President Rawlings Condemns Intelligent Design
Drawing from sources ranging from Cornell's founders to Voyager space missions, Interim President Hunter R. Rawlings III condemned the push to teach intelligent design in public schools Friday. The attack came during the president's State of... http://www.cornellsun.com/vnews/display.v/...4/435c7762cf891 "The desire to understand the world and the desire to reform it are the two great engines of progress." - Bertrand Russell -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Nov 18 2005, 08:30 PM
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
Well, yeah, a black hole would be the only thing that would have the raw power to strip material off of a neutron star. But I have serious questions as to what the process of such mass-stripping would look like -- it would seem to me that it would be so difficult to get fragments of a neutron star to break off of their parent body that it would tend to retain its cohesion until after it was safely within the Schwartzchild radius of the black hole...
-the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Guest_Richard Trigaux_* |
Nov 18 2005, 08:47 PM
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Guests |
QUOTE (dvandorn @ Nov 18 2005, 08:30 PM) Well, yeah, a black hole would be the only thing that would have the raw power to strip material off of a neutron star. But I have serious questions as to what the process of such mass-stripping would look like -- it would seem to me that it would be so difficult to get fragments of a neutron star to break off of their parent body that it would tend to retain its cohesion until after it was safely within the Schwartzchild radius of the black hole... -the other Doug Not sure. remember that a neutron star is about the same radius than the Schwartzchild sphere of a small black hole. So we can imagine that part of it is in, while most of it is still out. But at this stage, anyway, the complete coalescence is within some minutes or seconds of time, and the orbit is even no more circular, it is chaotic (and still more chaotic if the black hole rotates). So we can imagine that the neutron star is eaten by bits, each times it gets close enough. Anyway a neutron star is something extremely solid, but even this solidity is very weak in front of its gravitation. I am sure, there are some known example of "neutron star quakes" which occur when the rotation speed changes, and the shapes changes from more to less elliptic. So the gravitation of a neutron star is much stronger that its material solidity. Anyway a hand into the Schwartzchild sphere and the remainder of the body out, nothing can resist to this. We can imagine this tremendous catastrophe: each stripping is an enormous burst of energy, a series of cracks for some seconds before the remainder of the neutron star is swallowed, or it explodes from having no more enough gravitation left to resist the tremendous pressure of the neutronic matter. |
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Nov 19 2005, 01:10 AM
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
QUOTE (Richard Trigaux @ Nov 19 2005, 07:47 AM) Not sure. remember that a neutron star is about the same radius than the Schwartzchild sphere of a small black hole. So we can imagine that part of it is in, while most of it is still out. But at this stage, anyway, the complete coalescence is within some minutes or seconds of time, and the orbit is even no more circular, it is chaotic (and still more chaotic if the black hole rotates). So we can imagine that the neutron star is eaten by bits, each times it gets close enough. Note that orbits within about 3 Rs are unstable (allthough this can be less in a Kerr (rotating) black hole. So I don't really think we can imagine an orbit with part of the neutron star inside the Event horizon. QUOTE Anyway a neutron star is something extremely solid, but even this solidity is very weak in front of its gravitation. I am sure, there are some known example of "neutron star quakes" which occur when the rotation speed changes, and the shapes changes from more to less elliptic. So the gravitation of a neutron star is much stronger that its material solidity. Anyway a hand into the Schwartzchild sphere and the remainder of the body out, nothing can resist to this. Neuton stars are not "extremely solid" on the contrary most of there interior is superfluid. Only the crust is solid which is where the quakes occur, when, as you say the shape of the star changes. QUOTE We can imagine this tremendous catastrophe: each stripping is an enormous burst of energy, a series of cracks for some seconds before the remainder of the neutron star is swallowed, or it explodes from having no more enough gravitation left to resist the tremendous pressure of the neutronic matter. I'm not in a position to think about this much at the moment (a cold is stopping my brain from working!) but my first guess would be that the NS would be consumed pretty much whole. The only other scenario I can think of would be where tidal effects stretch the star so such an extent that gravity is no longer able to hold it together (like as been said above) however I don't think this likley for the following reasons: 1) NS's are really small so you would need one hell of a tidal force in the first place. 2) NS's hold there shape really well, these are objects that can rotate 100's of times per second and still stay together in a roughly sperical shape so an even higher gradient is needed. 3) for this to work the NS would have to be tidally locked to the BH this is hard due to the very good level of symmetry of the NS and the high rotation rate. 4) the NS would have to be fairly close to the lower mass limit which (I think) is probably quite rare. I just don't think the gravitational gradient is strong enough to do this, even within the last stable orbit of a BH. (Note no calculations done to justify all this, just belef ) James -------------------- |
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Guest_Richard Trigaux_* |
Nov 19 2005, 12:33 PM
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QUOTE (jamescanvin @ Nov 19 2005, 01:10 AM) Note that orbits within about 3 Rs are unstable (allthough this can be less in a Kerr (rotating) black hole. So I don't really think we can imagine an orbit with part of the neutron star inside the Event horizon. Neuton stars are not "extremely solid" on the contrary most of there interior is superfluid. Only the crust is solid which is where the quakes occur, when, as you say the shape of the star changes. I'm not in a position to think about this much at the moment (a cold is stopping my brain from working!) but my first guess would be that the NS would be consumed pretty much whole. The only other scenario I can think of would be where tidal effects stretch the star so such an extent that gravity is no longer able to hold it together (like as been said above) however I don't think this likley for the following reasons: 1) NS's are really small so you would need one hell of a tidal force in the first place. 2) NS's hold there shape really well, these are objects that can rotate 100's of times per second and still stay together in a roughly sperical shape so an even higher gradient is needed. 3) for this to work the NS would have to be tidally locked to the BH this is hard due to the very good level of symmetry of the NS and the high rotation rate. 4) the NS would have to be fairly close to the lower mass limit which (I think) is probably quite rare. I just don't think the gravitational gradient is strong enough to do this, even within the last stable orbit of a BH. (Note no calculations done to justify all this, just belef ) James Neutron stars hold their shape from gravitation which treats them as if they were fluid, even the super-resistant crust. In the case of super fast rotating neutron star, they keep from flying appart from the intense gravitation field, not from the resistance of the crust. The phenomenon of the black hole stripping the neutron star would take place during some seconds, during the very last chaotic orbits. The smaller the black hole, the better the chance for this scenario (a giant galactic black hole would swallow the neutron star at once and entirely). Especially that neutron stars are often larger than black holes. Anyway the gravitation field and gradient of a black hole is larger than the one of a neutron star, so that there are many chances to see the neutron star split even in the case it comes straight ahead on the black hole. |
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Nov 20 2005, 01:01 AM
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
QUOTE (Richard Trigaux) Neutron stars hold their shape from gravitation which treats them as if they were fluid, even the super-resistant crust. In the case of super fast rotating neutron star, they keep from flying appart from the intense gravitation field, not from the resistance of the crust. Note, I didn't make any ludicrous claims that the structual properties of the crust had anything to do with holding the NS star together as your reply seems to imply. QUOTE (helvick) Would heating\convection effects as we know them have any meaning in a superfluid? No, and not only that but the intense magnetic fields would also goven the interior motion over any convection effects even if it wasn't superfluid. QUOTE (helvick) Gravitional forces at the surface are 100 billion g, that's a hell of a lot of force keeping it spherical but the centripetal acceleration at the surface is almost exactly the same (assuming it's a 20km sphere rotating at 1000 revs/sec that comes to about 80 billion g). So the surface (at the equator at least) is balanced more or less on a knife edge - bring that close to anything that is massive, let alone a black hole, and the whole thing would probably shed outler layers catastrophically. 1000 Hz is a little fast, the fastest known pulsar is around 1.5ms I beleve (600 Hz) and note millisecond pulsars are extremly uncommon compared to your average common or garden NS (and probably more massive and hence more stable to disruption) The thing that makes me think that it would not be disrupted by ths method is that even using your very fast 1khz model you stiil have tens of billions of g's to overcome but not only that you've got to accelerate the matter to escape velocity within (less than) half a revolution else it's going to get to a position where the tidal force vanishes and it will fall back to the surface. QUOTE (dvandorn) I say again, I'd want to see what the process of stripping mass off of a neutron star would look like. And, for something as incredibly dense and difficult to break pieces off of as a neutron star, would the Roche limit actually occur inside the Schwartzchild radius of the black hole? My gut feeling is that it would -- the neutron star, I think, ends up getting swallowed whole no matter what you do... That's my gut feeling also. However I beleve the final accretion of material onto a BH is extremely complex and all this speculating is rather pointless without some rather complex simulation to back it up. I've done a bit of work in this field looking into jet production (jets are the day job) and it is very poorly understood (The fact that jets are produced at all tells you something complicated is going on!) James -------------------- |
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