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Author Topic: The Shape of Neutron stars ?  (Read 5982 times)

Offline neilep

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The Shape of Neutron stars ?
« on: 25/07/2007 22:47:28 »
Neutron Stars spin very fast don't they ?

Now I know they are extremely dense but does the extreme rotation speed change their shape from a  round ball to a disc ?



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Offline DoctorBeaver

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The Shape of Neutron stars ?
« Reply #1 on: 25/07/2007 22:53:14 »
I don't think so.

They are made of neutrons which, in turn, are made of quarks. The quarks are bound together incredibly strongly so it is unlikely that centrifugal force would cause any distortion at that scale.

Neutronium itself is incredibly dense (more dense even than Benny from Crossroads) so the gravitational field at the surface would probably be sufficient to hold the overall shape as a sphere.
 

Offline Karen W.

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The Shape of Neutron stars ?
« Reply #2 on: 25/07/2007 22:55:34 »
Yes, you are improving! Neily What is a Neutron Star..? That one is new to me.

Thanks Doc!
 

Offline DoctorBeaver

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The Shape of Neutron stars ?
« Reply #3 on: 25/07/2007 23:10:13 »
Karen - a neutron star is a star that has gone supernova and subsequently collapsed. When a star goes supernova, its core is compressed and the star's density increases to an incredible level - 1 teaspoonful of typical neutron star material would weigh 100 million tons.

This incredible density arises because towards the centre of the star there are fewer electrons and more neutrons. The neutrons are therefore pressed together rather than being separated by electron clouds. As the vast majority of the mass of an atom is in the nucleus, this means that most of the mass is preserved but squeezed into a very small area. A star that originally had twice the mass of our sun would compress to a sphere about 30,000 times smaller than our sun.

It is only a small step between a neutron star and a black hole. If the star was 5 times the mass of our sun it would collapse to form a black hole, any smaller and it would become a neutron star.
 

Offline neilep

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The Shape of Neutron stars ?
« Reply #4 on: 25/07/2007 23:20:00 »
.
 

Offline DoctorBeaver

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The Shape of Neutron stars ?
« Reply #5 on: 25/07/2007 23:23:49 »
 

Offline Karen W.

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The Shape of Neutron stars ?
« Reply #6 on: 25/07/2007 23:25:04 »
Karen - a neutron star is a star that has gone supernova and subsequently collapsed. When a star goes supernova, its core is compressed and the star's density increases to an incredible level - 1 teaspoonful of typical neutron star material would weigh 100 million tons.

This incredible density arises because towards the centre of the star there are fewer electrons and more neutrons. The neutrons are therefore pressed together rather than being separated by electron clouds. As the vast majority of the mass of an atom is in the nucleus, this means that most of the mass is preserved but squeezed into a very small area. A star that originally had twice the mass of our sun would compress to a sphere about 30,000 times smaller than our sun.

It is only a small step between a neutron star and a black hole. If the star was 5 times the mass of our sun it would collapse to form a black hole, any smaller and it would become a neutron star.

Thanks Doc! That answered two of my questions. I cannot imagine a teaspoon of of a typical Neutron star weighs 100 million tons.. I would hate to know what a not so typical one would weigh I cannot fathom anything that small weighing so much!
 

Offline Karen W.

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The Shape of Neutron stars ?
« Reply #7 on: 25/07/2007 23:25:40 »
 

Offline Soul Surfer

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The Shape of Neutron stars ?
« Reply #8 on: 26/07/2007 00:51:03 »
Rotating neutron stars would exhibit a flattend spheroidal shape although I am not sure how flattened it would be at the limit of stability but it would not be anything like a disc.

neutron stars are about one and a half times as heavy as the sun only a few miles across and not very much bigger than a black hole of the same mass
 

Offline DoctorBeaver

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The Shape of Neutron stars ?
« Reply #9 on: 26/07/2007 07:53:47 »
Ian - don't you think that gravity & the strong force would hold it as a sphere despite the rotation?
 

Offline Soul Surfer

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The Shape of Neutron stars ?
« Reply #10 on: 01/08/2007 10:12:05 »
No there would always be some oblatenes because of the angular momentum in the rotation.  It is calculated that the surfaces of neutron stars would be extremely smooth because a cliff one micron high would represent an enormous energy difference and cause great stress on material even if it was quite rigid.
 

Offline neilep

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The Shape of Neutron stars ?
« Reply #11 on: 01/08/2007 13:41:11 »
Thank you IAN (and everybody else)....

Neutron stars could then be the smoothest things in the universe.

How close is a Neutron star then to becoming a black hole ?

Say for instance, two neutron stars collided.....would that do it ?
 

Offline Soul Surfer

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The Shape of Neutron stars ?
« Reply #12 on: 01/08/2007 23:33:16 »
Yes.  A neutron star is very close to being a black hole and tend to have a very restricted mass range like white dwarfs.
 

Offline DoctorBeaver

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The Shape of Neutron stars ?
« Reply #13 on: 02/08/2007 08:47:49 »
If a star was 5 solar masses of more it would form a black hole instead of a neutron star.

It has been theorised that neutron stars with 1.5 - 1.8 solar masses (optimally) could form quark stars. The theory is that the neutrons would break down under the pressure into their constituent quarks.

So, again theoretically, adding more mass to a neutron would cause it to become a quark star. Add more mass and you get a black hole.

A star needs to have 5 solar masses or more to collapse to a black hole so, if the quark star theory is correct, 2 neutron stars colliding would possibly form a quark star rather than a black hole.
« Last Edit: 02/08/2007 08:49:56 by DoctorBeaver »
 

Offline syhprum

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The Shape of Neutron stars ?
« Reply #14 on: 02/08/2007 09:14:25 »
I there any way we could distinguish between a normal Neutron star and a Quark star other than the measure of its mass and theoretical considerations?.

Take a look here http://space.newscientist.com/article/dn9068-starquake-explosion-rips-neutron-star-open.html
« Last Edit: 08/08/2007 08:33:28 by syhprum »
 

Offline Soul Surfer

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The Shape of Neutron stars ?
« Reply #15 on: 04/08/2007 10:01:51 »
There is very little if any difference in the external appearance of a neutron or a quark star from a distance.  There may be a steady change as to whether the constituent particles are bound as nucleons (protons neutrons etc) or as individual quarks in some sort of asymptotically free interactions.  After all the whole thing is really a gravitationally bound nucleus with electrons batting around to create a neutral plasma

Remarkably little is understood about the detailed structure of the nucleii of the elements.  It is known that there are preferred shells of higher stability like in the electron shells in atoms but I do not think there is yet a good theory as to why the shells have the values that they do or total agreement as to the structure.
 

Offline esecallum

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The Shape of Neutron stars ?
« Reply #16 on: 06/08/2007 12:11:38 »
Ian - don't you think that gravity & the strong force would hold it as a sphere despite the rotation?

depends on spin speed.
 

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The Shape of Neutron stars ?
« Reply #16 on: 06/08/2007 12:11:38 »

 

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