Invoking The Voyagers Against Id Options

[ljk4-1]

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

[dvandorn]

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

[Guest_Richard Trigaux_*]

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.

[jamescanvin]

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.

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.

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

[Guest_Richard Trigaux_*]

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.

[dvandorn]

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.

That's what I meant when I said that I didn't think a neutron star would lose its cohesiveness enough to allow significant amounts of matter to be stripped. I wasn't thinking in terms of a solid body that couldn't be broken -- I was thinking of the gravitation holding it so tightly together that the only way anything, including a black hole, could tear it apart would be for the neutron star to barrel into the black hole -- and that the neutron star would be "swallowed" before any significant amount of mass could be stripped.

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...

-the other Doug

[Guest_Richard Trigaux_*]

dvandorn, I think only a calculus or simulation would tell us what scenario is possible, the neutron star swallowed at a whole, or it being stripped during the last chaotic orbits around the black hole. My personnal inclination is for the second scenario, but...


if it is stripped, the result may be tremendous. The surface of a neutron star is relatively cold, while the inner fluid are at million degrees or more. So exposing it at the surface may produce burst of gamma rays. There is an example of this, a relatively close neutron star (around 400 light-years) had a small adjustment of shape, allowing liquid to come on the surface. This only produced enough gamma rays and X rays to disturb Earth's ionosphere and affect radio transmissions! So tearing a neutron star may be a really horrible thing...

By the way, neutron stars are cooling, and in the proces they may have plate tectonics, volcanoes, etc. Or they have not, due to the solidity of the outer crust, and they cool only by heat diffusion through this crust.

And the inner fluid? It surely undergoes some convection. And magnetic lines, etc. like in Earth's core.

And superfast neutron stars, what shape do they get? Ellipsoids? peanuts? or more complex? How do they adjust their shape?