Neutron Star

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

  1. BennettLink Registered Member

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  3. BennettLink Registered Member

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    brucep likes this.
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  5. brucep Valued Senior Member

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    Prof. Link
    For somebody like me the arXiv has been my main access to the literature. I can't remember coming across any real garbage in the arxiv When I first started reading they had a peer review process. Then they switched to the recommendation process. Reputation means a lot. I think. LOL. How do you feel about the arXiv. It would be very interesting to read your comments.
     
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  7. BennettLink Registered Member

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    Dear Brucep,

    The arXiv is one of the most important creations in scientific publishing. It is just as the name implies, a repository or archive; it is not a journal. Typically people put their papers there at the same time they submit to a journal for peer review, with an indication that the work has not yet passed peer review. More conservative people post their work there only after the paper has been accepted for publication by a journal. What's great about the arXiv is that important work becomes available right away, and we no longer have to wait months for the paper to come out in print.

    Anyone can post on the arXiv. There is no recommendation process and there was never a peer-review process. There has been some talk of having peer review, which would completely eliminate the need for all other journals, but I don't think this will happen; the arXiv will be left open. The appearance of the arXiv has forced publishers to be more open about access.

    So keep in mind that what you read on the arXiv may not have been peer reviewed. If you see, for example, "To appear in the Astrophysical Journal", then it has passed peer review. If it says, "Submitted to the Astrophysical Journal", it has not yet passed peer review. Hence, people often submit revised versions. Think of the arXiv as a way for people to let the world know what they have been working on.

    You might wonder what stops people from posting rubbish. They can, but if other people start complaining, or the moderators of arXiv get suspicious, the perpetrator gets forever blacklisted.

    The wiki entry is informative if you are interested in the history of the arXiv.

    Best,

    Bennett
     
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  8. paddoboy Valued Senior Member

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    The most likely being in my opinion, that in the early part of the history of the Universe, our first stars, were extremely large, compacted rather closely together and with relatively short life spans of 10s of millions of years.
    When these stars went supernova, BHs resulted and many mergers took place due to the compactness nature of the stars.

    As Rajesh has been told many times before, cosmology makes many logical assumptions, based on common sense, the known laws of physics and GR, and what GR and physics predicts.
    We assume BHs exist without direct observation, by the effects on matter/energy and space/time within certain regions, by the same token we can reasonably assume that a BH within the EH will have certain properties such as spin, without getting any direct information from inside the EH.....
    We assume the Universe to be Isotropic and homegenous due to our observations of a rather large sample size.
    We assume the methodology of the mechanics of stars by nuclear fusion, while never really sampling or directly observing such mechanisms.
    From his history on this forum over many threads, he appears to not accept any "reasonable logical assumptions" without direct knowledge and proof.
    That's actually a shame, because other then that failing, he appears quite smart.
    He may object to me raising these past issues re his view on cosmology in general, with regards to this thread being on his paper, but in my opinion, when his past threads are examined even lightly, a mission, and an agenda appears to me at least to be obvious. In that respect, I see the raising of past issues as helpful and revealing in his early revelation of doubting the existence of BHs to eventually the paper in question.
     
  9. paddoboy Valued Senior Member

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    Professor Link:
    one more general question on Neutron stars and White Dwarf stars.
    Which is hotter, and which would maintain its heat longer before radiating it away?
    I know a WD takes many millions, even billions of years to cool down, [possibly longer then the current age of the Universe] and become a Black dwarf or cinder, and as yet we have never been able to discover a Black cinder after it has lost all its heat.
    On the other hand, finding such a beast would be notoriously difficult I would imagine.

    So how long for a Neutron star to cool down? Considering it is composed of mainly neutrons as distinct from a WD.
     
  10. BennettLink Registered Member

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    Paddoboy,

    A neutron star has a surface temperature somewhat above 10^6 K shortly after its birth, and cools little for the first 10^5 yr. After that, it drops to 10^5 K in about a million years. A white dwarf cools from about 30,000 K to 5,000 K in about a thousand years. On a logarithmic scale, a white dwarf cools more rapidly.

    Best,

    Bennett
     
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  11. paddoboy Valued Senior Member

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    OK, thanks...I did have a few things askew in that regard, particularly about WD temperatures.
     
  12. brucep Valued Senior Member

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    Thank you.
     
  13. RajeshTrivedi Valued Senior Member

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    Prof Bennett,

    ..............Causality is never violated. If you assume p=c^2 rho in the TOV equation, the causal limit, for all densities and pressures, you will never encounter a situation in GR in which any of the stellar matter violates causality by moving out of its light cone. This conclusion does not depend on the composition of the object or any other properties. This is true even during collapse. This is why (4/3) Rs is a robust number.Because p=c^2 rho is enforced in taking this limit, causality can never be violated. It's important to understand this........

    Generally I have a decent grasping power, but I am repeatedly failing to understand what you are saying on this point.......

    1. In equations as per the original reference posted by me, the figure 4/3 Rs is arrived by putting p = rho * c^2 and a limiting condition for r is arrived at 4/3Rs....

    Am I incorrect in understanding this conclusion that if core size < 4/3 Rs, then causality will be violated, and since causality can never be violated so core size per say cannot go below 4/3 Rs, something must happen ?

    In all the posts you have very clearly stated that causality is never violated, fine, I understood, but when an NS due to accretion starts collapsing towards Rs and then to r = 0, theoretically it will encounter a situation leading to causality violation, so what happens ?
     
  14. RajeshTrivedi Valued Senior Member

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    I do not find BH as common sense conclusion, in fact if any one other than of course you, states that BH can be hypothesized simply by common sense, then that person needs to define his common sense.....Come on Paddoboy, tell a layman that earth will be reduce to almost a pin head size (he won't understand point or r =0), his common sense will tell you to get lost...

    Both are not assumptions !! Hardcore observation based theories.

    I am smart and I know that....thank you. And I also have the right to make mistakes or learn more......I question things and If I do not like or understand I question them...........

    BH does not make common sense to me, so I raise this.....in fact Paddoboy, this singularity business does not make any common sense to many Physicist too....and I am quite sure the day is not far off when we would get a more realistic theory of BH etc.
     
  15. RajeshTrivedi Valued Senior Member

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    I read it fully, looks quite coherent.....

    No comparison is made between the speed of sound and speed of light........Look at this from a signal transmission point of view.......sound propagation can act (rather does) as signal transmission mechanism, so it cannot be faster than the speed of light....the comparison stops with that statement.

    General high school Physics has various relationship with respect to sound speed in Gas, Liquid and solids.....since Neutron Star is theorized as fluid, so pressure Vs density (Compressibility, Bulk's Modulus) comes into picture to arrive at the speed of sound inside NS, and this speed cannot be more than c......speed of sound = Sqrt(p/Rho). And you get r = 4/3Rs below which this aspect will be violated, and this is what first raised between me and Q-Reeus and later on raised explicitly by Prof Hamilton........

    I have two fold submission on this..

    1. This condition of causality violation ( c^2= p/Rho) cannot come as long as we are able to compress the material, for the NS onwards, the incompressibility aspect (if at all) will manifest only below extreme Packing radius (Rp), and the proposed BNS is formed before extreme Rp.....So Prof Hamilton objection is technically right but not relevant for BNS...

    2. 4/3 Rs is > Rs......so how a core surpasses this barrier to become smaller than Rs......think objectively, and attempt to clear these two points........don't proceed with a pretext that questions are frivolous......proceed with Physics around you..
     
  16. Q-reeus Banned Valued Senior Member

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    That's not my understanding - afaik one needs to be either in academia or at least have an article specific endorsement from some recognized authority in academia. [edit: or closely related - e.g. research center/institute] Hence why many without such connections are forced to choose say viXra instead. A quick check at arXiv.org site yielded this: http://arxiv.org/help/endorsement
     
    Last edited: Apr 29, 2015
  17. paddoboy Valued Senior Member

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    You are again manufacturing scenarios that specifically will support your erroneous line of thinking.
    A bloke called Michell, theorised a Newtonian version of a BH as far back as 1879. He called it a Dark Star, based on the simple concept that as an mass got denser, its escape velocity increased. So theoretically speaking he imagined a mass so dense, the escape velocity was equal to "c".
    I suggest that it is you who needs to redefine your common sense, in railing against 20th/21st century cosmology, without any specific authority or expertise in that area.
    Telling a layman, and perhaps explaining to him the simple concept of an atom via an analogy of placing a pea in the middle of the Sydney Cricket Ground [representing the atomic nucleus] would see the electrons orbiting out near the outer grandstand seats, the rest being just empty space, noting of course how much compression could take place, is quite understandable since I have tried it myself at a recent old boys reunion. So please again, stop trying to manufacture conditions to support your shaky position in all of this.
    Wrong. Both are assumptions based on other physical theories and incorporating logic and common sense in both cases.....just as it is logical and reasonable to infer the Kerr metric to be spinning, and just as logical how we can infer BHs by the effects on spacetime and matter/energy, especially since no other known aspect or entity that we know of can explain that.
    But the above assumptions [which you apparently missed

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    ] are continually being questioned by you.




    Self praise is no recommendation, and humility is something that you lack...Something that the great man Einstein had plenty of.
    Some men of religion are also highly intelligent folk...No one would deny that, but they also question science and its methodology and conclusions. Is this your agenda?
    What detracts from your relative smartness is of course whatever agenda it is that you are pushing [religious???, I'm not sure] to ignore the data, theories and knowledge obtained by the giants of the present and past, along with the state of the art equipment that they have access to, and that you don't, and think that you are the purveyor of truth or some great discovery.

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    As I have told you many times, if you had anything of substance that had promise, you would not be here. You would be knocking on the doors of Academia screaming from up high about what you had found.
    Instead of that you present it on a science forum, opened to anyone and obviously opened to plenty with questionable motives.
    All one needs to do is check out the fringe section!
    You certainly have the right to make a mistake but the problem is you are not apparently learning from your mistakes.
    Your first big mistake was questioning GR without any qualifications or professional learning. Your other mistake is the way you tried to reflect on this forum, a position totally opposite to what you are trying to present now.
    You have been also wrong over many threads on aspects of BH physics and yet you have never admitted you were in error. That is not very smart either...In fact that is dumb.
    Your first thread asking questions one in particular about why galaxies do not collapse into BHs.

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    Then you progress to an expert, questioning GR and BHs, and then finally this paper through a totally apparently discredited publishing company. Something I have questioned you on many times and something you continually ignore....which leads me to conclude a religious agenda of sorts, like so many others we have had here.

    BHs certainly question what we may on face value class as intuitive, but that has happened before as we gain knowledge through science. We thought the Earth was the center of the Universe, with everything revolving around us...It certainly seemed that way, Sun rose in the East revolved around to set in the West and circled to again rise in the East 24 hrs later.....Einstein also questioned the previously intuitive nature of space and time both being absolute.
    So please do not insult my intelligence by suggesting you as a non expert without professional learning or study, can come along, overturn 20th/21st century cosmology by publishing a paper in a questionable company...a paper that has been thoroughly debunked as nonsense.
     
    Last edited: Apr 29, 2015
  18. RajeshTrivedi Valued Senior Member

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    What has religion got to do with my posts on this thread ?? Can you please pin point ??

    You have a situation Paddoboy, which is genuine and unavoidable.

    The situation is by your own admission you lack formal higher education, by your own admission you are a great enthusiast of cosmology, by your own admission you cannot contribute to science.......under the circumstances you have restrained ability (or you feel so) to propose anything new.....so your best bet is stick to mainstream, do not question them, this is the only way by which you can (and you are) getting acceptability.

    PS : I am not deriding you by making above statement, I am putting my appreciation for your enthusiasm and more than club level knowledge of subject...But since you tend to cross line with me, I must put things in right perspective.
     
  19. paddoboy Valued Senior Member

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    I have no objection to religious folk other than they are obviously blinded to the truth and when they rail against science. You appear to fit this bill..
    I have no situation other then a love of cosmology and those that are gaining more and more knowledge in that area of expertise.
    Correct, I am unable to contribute to science but I can contribute to a science forum correctly. I may also lack a formal education which I openly admit to, but you lack any qualifications and expertise in this discipline of science.
    This brings into question your lack of humility in thinking you are rewriting 20th/21st century cosmology.
    You are of course fooling yourself due to your agenda. Me?? Like Newton, I'm proud to be seeing as far as I do, by standing on the shoulders of giants [and authoritive experts]

    We are both in the same boat...both unqualified and lay persons, differing only in the fact that I do not have an inflated ego, nor any agenda to push...religious or otherwise.
    I'm also not deriding you, just showing and putting into perspective your arrogance, your delusions of grandeur, your agenda, and your stubborness in refusing to accept any and all authoritive expert opinions.
     
  20. Q-reeus Banned Valued Senior Member

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    Not at all disputing Prof. Link's answer in #327, but your question betrays a lack of basic physics understanding. All other things being equal (e.g. WD and NS masses are quite comparable), radiated power ~ A*T^4, where A = pi*r^2 is surface area and T the surface temp in Kelvin. You were already aware of the enormously larger size of a WD wrt NS, right?
     
  21. paddoboy Valued Senior Member

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    Sure, but I'm also aware one is composed of mainly neutrons.
     
  22. Q-reeus Banned Valued Senior Member

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    Well unless you are implying a vastly different surface emissivity (and surface material states between a WD and NS are afaik not far different), only really net mass, surface area, and of course initial temp are what really matter. Interior heat transport may be a limiting factor at perhaps initial birth when temps are extremely high in a NS - but there I'm wandering into territory best left for the likes of Prof. link. And of course this is, as customary here at SF, yet another sidetrack.
     
  23. RajeshTrivedi Valued Senior Member

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    The temperature aspect has one more rider......in the inner core the neutrons of the neutron star are actually pretty cold......again a territory which is best left for the likes of Prof Link only....
     

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