Neutron Star

Discussion in 'Astronomy, Exobiology, & Cosmology' started by RajeshTrivedi, Apr 7, 2015.

  1. paddoboy Valued Senior Member

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    http://physicsworld.com/cws/article/news/2011/mar/02/neutron-star-has-superfluid-core

    Neutron stars should exhibit both superfluidity and superconductivity, according to two independent groups of scientists. The researchers studied the neutron star in the supernova remnant known as Cassiopeia A, and found that its core should exist in a superfluid state at up to around a billion degrees kelvin, in contrast to the near absolute-zero temperatures required for superfluidity on Earth.

    Neutron stars are extremely dense objects that form when massive stars run out of nuclear fuel and collapse in on themselves. The enormous pressure within the star forces almost all of the protons and electrons together to form neutrons. Astrophysicists would like to know more about the properties of this ultra-dense matter, and one way to do this is to study exactly how neutron stars cool. The object at the heart of Cassiopeia A, which is about 11,000 light-years away, is ideally suited to such an exercise because, unusually, it has both a well established age – about 330 years – and a well known surface temperature – around 2 million kelvin.
    Last year, Craig Heinke of the University of Alberta in Canada and Wynn Ho of the University of Southampton in the UK analysed 10 years' worth of X-ray data from NASA's Chandra satellite and found that the Cassiopeia A neutron star's surface temperature has dropped more quickly than expected – by about 4% between 2000 and 2009.
    Cooper pairs and neutrinos
    In the current work, groups led by Dany Page of the National Autonomous University in Mexico and Peter Shternin of the Ioffe Institute in St Petersburg, Russia, say that this rapid cooling can be partly explained by invoking the zero-viscosity state of matter known as superfluidity. They argue that when the temperature of a neutron star falls below a certain critical value it becomes energetically favourable for neutrons inside the star to form Cooper pairs – the basic unit of the superfluid state – and that the energy released as a result could be easily removed from the star in the form of neutrinos

    extracts:
    A neutron star should exhibit superfluidity when its temperature drops below about 800 million kelvin and that proton superconductivity could take place at up to 2–3 billion kelvin. Page and colleagues, meanwhile, calculate the superfluid transition temperature to be around 500 million kelvin.
     
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  3. paddoboy Valued Senior Member

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    I accept responsibility for the side track, but the Professor has answered the questions on the paper, and I thought a few questions on NS in general would throw more light on these stellar remnants.
     
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  5. Q-reeus Banned Valued Senior Member

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    You seem to be referencing inner core temp to elsewhere including surface temp. Don't know where you got that idea from but it's quite wrong and the inverse is true. See my response to paddoboy.
     
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  7. Q-reeus Banned Valued Senior Member

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    Right well anyway I have some corrections to make re my #337 & #339.
    Apart from ignoring the dominant contribution to very initial NS cooling from neutrinos, one thing I assumed without checking was that the internal temp profiles of WD's and NS's are comparable. Turns out to be roughly true:
    https://en.wikipedia.org/wiki/White_dwarf#Radiation_and_cooling
    http://web.science.uu.nl/itf/Teaching/2011/MaartenKater.pdf (see fig. 5.3 p34 there)
    Almost uniform from core right out to ~ outer crust, then a steep drop. The details apparently can vary greatly across the range of both WD's and NS's. Hence need to talk in generalities.
    Another thing not mentioned was specific heat capacity. Can't say how the effective average values will compare given the complex internal profiles, but in general I would expect they would be quite comparable as Fermi gas stats should apply to both in large measure.

    So I did jump a bit too soon, but all-in-all, it's still true the overwhelmingly dominant difference in long-term cooling rates (even allowing for vastly higher initial NS temps) is owing to greatly different surface areas.
     
  8. BennettLink Registered Member

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    Dear Rajesh,

    You are incorrect. Induced collapse does not lead to causality violation. Why do you think it should?

    Note that the number of (4/3) Rs was obtained by considering a static configuration with p=c^2 rho. This limit follows from both the assumed equation of state (the strongest matter that is, at least in principle, physically possible) and from GR.

    We can play the mathematical game of letting the material be infinitely strong (infinite sound speed), which violates causality in the medium. This violates Special Relativity, but we can still play this mathematical game. Even then, the stable radius is (9/8) Rs > Rs, according to GR.

    Going back to matter that is physically possible, that is, matter in which the sound speed is bounded by c, if the object is forced to collapse, the sound speed could go down, but not up. The sound speed can never exceed c for any kind of matter under the assumptions of Special Relativity. It is physically impossible. As the object collapses the medium will not violate causality. SR and GR don't allow it.

    When you say that causality violation should occur, you are rejecting GR, because GR is always causal. GR makes the prediction that no material object can be static within (4/3) Rs. Therefore, your black neutron star violates GR.

    Do you concede this point?

    Best,

    Bennett
     
  9. BennettLink Registered Member

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    24
    Hi Q-reeus,

    Please reread that endorsement link. There is no mention of academic affiliations. You just need a track record in the arXiv, or someone on the arXiv who vouches for your work as being real science. This is to screen out pseudoscience and nonsense. A person writing a legitimate paper, which could even be quite speculative, will have no trouble getting an endorsement. A person trying to post pseudoscience or nonsense will have trouble.

    Best,

    Bennett
     
  10. dumbest man on earth Real Eyes Realize Real Lies Valued Senior Member

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    3,523
    ...first off...
    Welcome to SciForums BennettLink.

    Meant to Post this Video a few days ago...while discussion was on "jets"... :

    At any rate, this is a 25-minute Video titled : "The Largest Black Holes in the Universe", it has some very good computer simulations on a few different aspects of what has been discussed in this Thread...as far as Theoretical Cosmology is concerned.

    Seriously, anyone that is even remotely interested in the Topic of this Thread should find it an interesting and possibly even quite informative 25-minutes.

    Enjoy it in HD, if you can.
     
  11. paddoboy Valued Senior Member

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    27,543

    An amazing half hour of awesome scenarios dmoe...Thanks. I hope Rajesh watches it in its entirety.
    My only comment is in your mention of "theoretical cosmology" This conjurs up images of uncertainty and claims of guess work by many non students of cosmology, when in actual fact like any scientific theory, it is formulated and based on the extensions of the laws of physics and GR and how they apply to the situation in question, and of course observational and experimental data.

    As I pointed out to Rajesh, BHs of sorts, was first theorised by the simple application of Newtonian mechanics, and were called Dark Stars. It was at that time though [1783] thought to be too absurd, and the idea was pidgeon holed.
    Our present accepted theory of cosmology and BHs are based on what knowledge scientists and cosmologists have at this time.
    BHs of course can be easily invalidated if someone could explain the effects we observe on spacetime and matter/energy that in the first place promoted BHs as the likely outcome, on some other means or entitiy.
    Rajesh has given us BNS as an hypothesis, and subsequently, this has been shown to be in total contradiction to what we already are able to determine and also defies GR.
     
  12. paddoboy Valued Senior Member

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    A previous post of mine at post 334. The 1879 should be 1783.

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  13. dumbest man on earth Real Eyes Realize Real Lies Valued Senior Member

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    The theoretical sciences are what they are...
     
  14. brucep Valued Senior Member

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    All the cosmology is theoretical if it makes predictions for cosmological phenomena. For example all the models that have some basis in reality [crackpots excluded] make predictions for what the power spectrum should look like. The amazing thing is it is just recently, within the last 30 years, that cosmology became experimentally testable with the advent of the great CMBR experiments. Everything will remain theoretical because it has the possibility of falsification. Since I'm off topic I'll link this great site which explains what these cosmological measurements are and why they're being made.
    http://background.uchicago.edu
     
    Last edited: Apr 29, 2015
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  15. paddoboy Valued Senior Member

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    Exactly brucep, and what I was trying to say.
    In essence we all know that some scientific theories are so well supported and evidenced, that they are damn well near certain, [Evolution of course is certain, while Abiogenesis, the BB, SR/GR are not far behind] while remaining open for possible falsification.
     
  16. brucep Valued Senior Member

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    4,098
    As far as I'm concerned they're all certain in domain of applicability. All the cranks avoid the scientific rule.So they can think up any definition for theoretical as they want. Some act like if it's theoretical it's meaningless. There's another important word. Fact. Because I didn't include that I may have messed up. LOL.
     
    Last edited: Apr 30, 2015
  17. paddoboy Valued Senior Member

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    And this is what Rajesh hangs his hat on. The fact that we are unable in principle to get any information from across an EH...He conveniently ignores the fact that the prediction of BHs are based on indirect observation on spacetime, and matter/energy...nothing else can explain such turmoil, temperatures and velocity, he conveniently ignores the GR enforced compulsory collapse once a Schwarzchild radius is reached, and ignores gravity overcoming all other forces including strong nuclear as we approach the singularity/mass at the center, and substitutes an adhoc BNS scenario.
    All this from the position of a lay person and non professional [like myself] in this "state of the art scientific equipment" driven discipline of cosmology.
    It's akin to him telling a patient that needs a brain operation, to forget what the surgeons and specialist doctors have to say, as he has come up with a new solution to the problem.

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  18. brucep Valued Senior Member

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    Unlike most others I consider this thread somewhat of a success. The contribution by experts culminating with the detailed answers and comments by Professor Link. You asked some good questions, thanks, and found some good links. Tashja is to cool. Some people refuse to learn but that's par for this course. Collapsed stars were the subject of the two books I mentioned. The discussion about journals was really interesting for me.
     
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  19. RajeshTrivedi Valued Senior Member

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    Prof Bennett,

    You asked if I concede, may be I will take some more of your time, because I do not want to drop this discussion without getting full clarity. Thanks for your kind participation and prompt responses.

    Let me re align to situation.....

    1. I am not saying that causality violation should occur, GR / SR does not allow it and it will not. So there is no dispute on this point....

    2. For a stable structure 4/3 Rs is the limit, as derived by putting sound speed equal to c, and 9/8 Rs is the limit wherein sound speed will go to infinity....that is mathematical......thats clear as per detailed derivation on the reference paper.

    With this I am attempting to understand what you are saying....

    A. That an object of size less than 4/3Rs (and worst case 9/8 Rs) cannot be stable, since proposed BNS is inside EH (less than these two figures) and hence it cannot be stable... throw BNS out !!

    B. But if the object starts collapsing due to gravity then dynamically (in very fast transit) it can get below 4/3Rs (or 9/8Rs) forming the stellar BH.............point is that under such collapse it is not taken as stable object and hence permissible below 4/3Rs..........

    Is this what you are saying (A and B above) ?

    If so, then there is another point to handle.....


    (i) The derivation of 4/3Rs (and 9/8Rs), I feel, is based on hydro-static equations, which is applicable when matter is under degenerate state, under a very high density.........It is not a general equation for all mass. For example take Brucep calculations for UMBH, the density when the object is of Rs size is hundred times rarer than that of air...so obviously this 4/3Rs and 9/8Rs is not applicable....

    (ii) This is what I have stated that when the core mass is below 3.24 Solar Mass, the NDP will happen outside the Rs, in that case 4/3Rs and 9/8Rs will come into picture.

    (iii) For core mass higher than 3.24 Solar Mass, the NDP will manifest fully inside Rs (when the core size is less than Rs), in such scenario (for Core > 3.24 Solar Mass) 4/3 Rs and 9/8 Rs poses no threat and such eventuality will appear much below Rs.

    (iv) So straight away saying that BNS unstable because it is smaller than 4/3Rs and 9/8 Rs is unsustainable, simply because BNS would form only if core mass > 3.24 Solar Mass, and with such mass range 4/3Rs and 9/8Rs are irrelevant figures. These figure are relevant for mass < 3.24 Solar Mass only.

    Hope I am able to explain the point. request to other members who have understood the point, pl chip in, so that it can be resolved faster...
     
  20. paddoboy Valued Senior Member

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    In my view there would be no BNS stable or unstable even for a fleeting second, as it appears you are saying.
    Reasons being in my basic layman's view, and as I have supported with references in the past] the strong nuclear force is totally overcome by gravity, hence the NS would be torn apart into its most basic constitutions before the EH is even formed...or possibly at the EH.
    Once inside the EH of course all paths lead to the Singularity/mass at the center, and would reach there in a very small but finite time.
    But I'll certainly be willing to be corrected by the Professor if that is the wrong scenario....
    In any case there is a totally huge difference between an entity that is stable, or one that is unstable, and which cannot at all possibly survive for any reasonable time frame inside the EH, hence it is stretching things to the ridiculous and beyond to refer to such instability, for such a small time frame as real in any sense at all.
     
  21. RajeshTrivedi Valued Senior Member

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    Paddoboy, as stated earlier on the nuclear force, concept of nuclear force keeping protons / neutron together is not so direct in case of NS and BH, simply because protons are not available and neutrons are in abundance.

    Secondly if you are referring to strong nuclear force among Neutrons only, then it is additive, kind of supporting the Gravity....gravity compacting the core, and Neutrons are also bonded by the Nuclear force......so where is the question of nuclear force getting overcome in this discussion...

    What do you mean NS would be torn apart before the EH is even formed ?? You are suggesting that NS would be torn apart without forming the BH ?? Is it a slip of tongue ?? My argument with Prof Bennett is exactly on this point only, that something must happen when NS core gets below <4/3Rs due to gravity by accrued mass on NS ? You are innocently supporting that view ??

    PS : We are discussing the formation, not the in fall into existing BH....
     
  22. paddoboy Valued Senior Member

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    Obviously neutrons are in abundance but the strong nuclear force is still present..
    In the scenario you are hypothesising, I'm saying before any NS turns into a BH, gravity will overcome the strong nuclear force, just as it does with any matter that eventually crosses the EH on its one way trip to oblivion and the Singularity/mass.
    But I'm certainly willing to be corrected by those proficient in the discipline.
    No slip of the tongue, and I also said also possibly "at the EH"
    What I'm saying is my view about a possibility, and at worst case scenario, even if this hypothetical BNS formed inside, it would be unstable and quickly disintigrate as gravity overcame the strong nuclear force. Possibly in a time frame equivalent to Planck time......but I admit I'm only guessing.
    Either of those scenarios at least surpass any possibility of a stable BNS.
     
  23. Q-reeus Banned Valued Senior Member

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    4,695
    True. Maybe what colored that perception was finding almost no exception to any physics arXiv articles being authored by any than those at Unis or research centers. Which is to be expected in a way as they are the prime generators/beneficiaries of 'publish or perish'.
    On another point there, I'm not sure of the seemingly subtle distinction between endorsement and where you wrote in #324 "There is no recommendation process...".
    That can obviously be a catch-22, but your following remark in principle gets one over that first hump...
    Pardon me for harboring some reservations, but aren't there powerful incentives for an endorser to take a very conservative line and shy away from anything even remotely speculative or at least 'novel'? A bit like in the risk capital game. Knowing just who to approach no doubt helps.
    No argument with that one.

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    Thanks again for valuable feedback Prof. Link.
     

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