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Thread: What is matter like on a neutron star?

  1. #1  
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    G'day from the land of ozzzzzzzz


    Neutron star is made up of Neutrons packed together to a density of about 10^17 Kg/m3. Thats the inner core. Some even say it is a composite matter with quarks.

    The outer core is some cases is Iron and various other elements that form an envelope.



    Supernova Explosions and the Birth of Neutron Stars
    http://adsabs.harvard.edu/abs/2008AIPC..983..369J


    Abstract

    We report here on recent progress in understanding the birth conditions of neutron stars and the way how supernovae explode. More sophisticated numerical models have led to the discovery of new phenomena in the supernova core, for example a generic hydrodynamic instability of the stagnant supernova shock against low-mode nonradial deformation and the excitation of gravity-wave activity in the surface and core of the nascent neutron star. Both can have supportive or decisive influence on the inauguration of the explosion, the former by improving the conditions for energy deposition by neutrino heating in the postshock gas, the latter by supplying the developing blast with a flux of acoustic power that adds to the energy transfer by neutrinos. While recent two-dimensional models suggest that the neutrino-driven mechanism may be viable for stars from ~8Msolar to at least 15Msolar, acoustic energy input has been advocated as an alternative if neutrino heating fails. Magnetohydrodynamic effects constitute another way to trigger explosions in connection with the collapse of sufficiently rapidly rotating stellar cores, perhaps linked to the birth of magnetars. The global explosion asymmetries seen in the recent simulations offer an explanation of even the highest measured kick velocities of young neutron stars.


    Hydromagnetic waves in a superfluid neutron star with strong vortex pinning
    http://adsabs.harvard.edu/abs/2008arXiv0803.0276V

    Abstract

    Neutron-star cores may be hosts of a unique mixture of a neutron superfluid and a proton superconductor. Compelling theoretical arguments have been presented over the years that if the proton superconductor is of type II, than the superconductor fluxtubes and superfluid vortices should be strongly coupled and hence the vortices should be pinned to the proton-electron plasma in the core. We explore the effect of this pinning on the hydromagnetic waves in the core, and discuss 2 astrophysical applications of our results: 1. We show that even in the case of strong pinning, the core Alfven waves thought to be responsible for the low-frequency magnetar quasi-periodic oscillations (QPO) are not significantly mass-loaded by the neutrons. The decoupling of about 0.95 of the core mass from the Alfven waves is in fact required in order to explain the QPO frequencies, for simple magnetic geometries and for magnetic fields not greater than 10^{15} Gauss. 2. We show that in the case of strong vortex pinning, hydromagnetic stresses exert stabilizing influence on the Glaberson instability, which has recently been proposed as a potential source of superfluid turbulence in neutron stars.


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  3. #2 What is matter like on a neutron star? 
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    Matter on a neutron star is obviously not in the form of an atom, what is matter on a neutron star?


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    A star is a wrestling match between the explosive forces of the core fusing light elements together into heavier elements and gravity. Most fusion releases energy according to Einsteinís equation. However, it takes more energy to fuse iron than is released by the process. So when the core of a star becomes iron, the core loses energy and the outer layers collapse under the pull of the starís gravity. The iron core is crushed so tightly that most of the atoms lose their electrons. The negatively charged electrons combine with the positively charged protons in the nucleus to form neutrons, a chargeless particle. The surface of a neutron star may be a layer of iron ions, iron nuclei that have been stripped of their electrons. The bulk of the star is made of neutrons that have been crushed together as densely as is possible without the entire mass of the star collapsing into a black hole singularity.
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    Quote Originally Posted by Arch2008
    A star is a wrestling match between the explosive forces of the core fusing light elements together into heavier elements and gravity. Most fusion releases energy according to Einsteinís equation. However, it takes more energy to fuse iron than is released by the process. So when the core of a star becomes iron, the core loses energy and the outer layers collapse under the pull of the starís gravity. The iron core is crushed so tightly that most of the atoms lose their electrons. The negatively charged electrons combine with the positively charged protons in the nucleus to form neutrons, a chargeless particle. The surface of a neutron star may be a layer of iron ions, iron nuclei that have been stripped of their electrons. The bulk of the star is made of neutrons that have been crushed together as densely as is possible without the entire mass of the star collapsing into a black hole singularity.
    It is able to be so small because there is no space between the protons and electrons, which also makes it a neutron, I guess that is why it can be so compact.

    How long does the transformation take for a red supergiant to turn into a neutron star after the gravity exceeds the outward force?
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    G'day from the land of ozzzzz


    This is an opinion:

    In the inner core of many long life stars there lives a compact core made probably from some form of degenerate matter.

    This compact core serves many functions:

    1) To keep the solar envelope from expanding.
    2) Control the heat release into the solar envelope.
    3) Give energy to the solar envelope.
    These are but a few.

    As the sun ages it produces all the elements from H upto Fe and Zn via fusion and heavy elements, that are unstable due to the solar envelope conditions. These eavier elements break down to Fe via fission.

    Over billion of years you end up with a large collection of Fe and varies amounts of elements upto Fe.

    The inner core over this period loses mass and because of this, it loses its abilty to :

    1) Hold the solar envelope together and allows it to expand into a giant.
    2) The lower mass of the inner core loses its abilty to control the heat with in the solar envelope and also the abilty of the rate of heat loss from the inner core.

    High enegy phontons are released into the solar envelope.
    The Fe being heaviest is found near the outer core.
    The Fe is hit by these high energy photons and during an endothermic fission chain reaction the Fe is broken down to He than to H than to Neutrons. These Neutrons find a home within the core and collect at an extremely fast rate.

    At the same time Fusion chain reaction occur within the solar envelope giving it enough energy to trigger the supernova.


    I do not think that Fe is found within the core, because its compaction has a Max orf 10^5 kg/m3. Although this is very dense, it requires a more compact body.

    Possibly a Neutron Composite that allows compaction upto about 10^18 Kg/m3.

    The difference between a proton and a Neutron is one electron. The protons when added with an electron make up a Neutron. Neutrons because of their Neutral charge allows for compaction compared to Protons their Max compaction is only about 10^5 Kg/m3.

    This link is quite intersting


    Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State
    http://adsabs.harvard.edu/abs/2007IJMPE..16.1165W

    Abstract
    With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultra-dense matter predicted to exist deep inside neutron stars and discusses the equation of state (EoS) associated with such matter.
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  7. #6  
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    Good job, Harry! I never gave up hope.

    Here's a link to neutron degeneracy:
    http://www.astro.virginia.edu/~jh8h/...utrondegen.htm

    Once the iron core fuses, the outer layers of the star collapse at nearly one quarter the speed of light, so the neutron star phase happens pretty darn quick.
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    G'day from the land of ozzzzzz


    Arch you said:
    Good job, Harry! I never gave up hope.
    Hope? ,,,,,,,,,smile,,,,,,,,,

    Once the iron core fuses, the outer layers of the star collapse at nearly one quarter the speed of light, so the neutron star phase happens pretty darn quick.
    The Fe does not under go fusion.

    What happens to Fe is:

    Photodisintegration
    http://en.wikipedia.org/wiki/Photodisintegration

    Photodisintegration is a physical process in which extremely high energy gamma rays interact with an atomic nucleus and cause it to enter an excited state, which immediately decays into two or more daughter nuclei. A simple example is when a single proton or neutron is effectively knocked out of the nucleus by the incoming gamma ray, and an extreme example is when the gamma ray induces a spontaneous nuclear fission reaction. This process is essentially the reverse of nuclear fusion, where lighter elements at high temperatures combine together forming heavier elements and releasing energy. Photodisintegration is endothermic (energy absorbing) for atomic nuclei lighter than iron and exothermic (energy releasing) for atomic nuclei heavier than iron. Photodisintegration is responsible for the nucleosynthesis of at least some heavy, proton rich elements via p-process which takes place in supernovae.

    But! stars are at different phases and supernova and Nova are not controlled by Fe levels.


    http://www.astro.virginia.edu/~jh8h/...utrondegen.htm

    Neutron Degeneracy
    Neutron Degeneracy Pressure: Quantum mechanics restricts the number of neutrons that can have low energy. Each neutron must occupy its own energy state. When neutrons are packed together, as they are in a neutron star, the number of available low energy states is too small and many neutrons are forced into high energy states. These high energy neutrons make up the entire pressure supporting the neutron star. Because the pressure arises from this quantum mechanical effect, it is insensitive to temperature, i.e., the pressure doesn't go down as the star cools. Similar to electron degeneracy pressure but, because the neutron is much more massive than the electron, neutron degeneracy pressure is much larger and can support stars more massive than the Chandrasekhar mass limit.
    This is quite interesting

    http://arxiv.org/abs/nucl-th/0412073

    Nuclear Clustering and Interactions Between Nucleons
    Authors: O. Manuel
    (Submitted on 19 Dec 2004)

    Abstract: Nuclear mass data provide EMPIRICAL evidence of: 1. Clustering of nucleons; 2. Attractive n-p interactions; and 3. Repulsive but symmetric n-n and p-p interactions after correcting for the repulsive Coulomb interactions between positive nuclear charges. These findings suggest a possible source of energy in neutron stars, in stars which formed on them, and demonstrate the need for a Theoretical understanding of 1. Interactions between nucleons; 2. Clustering of nucleons; and 3. Neutron-emission by penetration of the gravitational barrier surrounding a neutron star.

    Experiments with Z-pinch ,R, S and P processes may be a way of investigating.
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