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Thread: Neutron Star Binary PSR J0737-3039 and Frame Dragging

  1. #1 Neutron Star Binary PSR J0737-3039 and Frame Dragging 
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    I was reading about PSR J0737-3039 - a binary pair of stars thought to be neutron stars - and I came across this table in Wikipedia:

    Property..........................Pulsar A.............................Pulsar B

    Spin period...................23 milliseconds..................2.8 seconds

    Mass..........................1.337 solar masses..........1.250 solar masses

    Orbital period 2.4 hours

    (ref. http://en.wikipedia.org/wiki/PSR_J07...double_pulsars )

    I was wondering what effect frame dragging would have on this system. Do they appear to a distant observer (us) to be orbiting each other faster than their masses would otherwise indicate if they weren't rotating at such high rates?

    I ask this because both components are massive, compact, have high spin rates (especially pulsar A) and are very close to each other (~about 800,000 km according to a related article here: http://www.skyandtelescope.com/news/...tml?page=1&c=y )

    For those doubting Thomases out there, the last cited article claims that this system confirms four different aspects of General Relativity.

    Chris

    Edited to correct spelling error


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  3. #2  
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    In regard to my previous post, I tried using the formula for orbital periods to see what the orbital period without any frame dragging would be:

    The mass would be (1.25+1.337)=~2.587 solar mass

    The semi-major axis would be 400,000,000 meters

    When I plug these numbers into the WolframAlpha site, I get 45.21 min.

    (ref. http://www.wolframalpha.com/input/?i...30+kg&x=4&y=10 )

    When I make this calculation on paper I come up with ~2700 seconds (~45 min.).



    Chris


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  4. #3  
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    I'm gratified to know that my paper calculation matches the computer's result, but I'm still obviously doing something wrong. The published literature gives an orbital period of 2.4 hours, not 45 minutes.

    Chris
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    I find that, when I back-calculate using the values given by Wikipedia for these two neutron stars and their orbital period, the semimajor axis equals 866,000 km. The separation of these two neutron stars is therefore 1,732,000 km for an orbital period of 2.4 hr. - not 800,000 as has been published.
    (ref. http://www.wolframalpha.com/input/?i...E30+kg&x=6&y=7 )

    I've come to the conclusion that either the published orbital distance or the published orbital period must be wrong. I can't imagine how such a large discrepancy could find its way into a published article, though.

    Chris
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    I've checked articles from several publications and I've reviewed several of the research papers which they cite as sources. They're all using the same numbers for mass, period of rotation and separation.

    I calculated that the gravitational time dilation for these orbiting bodies would be 0.99999 (virtually none).

    Why don't my calculations match those of the professionals?

    Help!

    Chris
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  7. #6  
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    After 162 views and no replies I'm wondering if my question is so trivial as to not even warrant a reply or so perplexing that no reply is posible.

    Where's DrRocket when you need him?

    Chris
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  8. #7  
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    I don't think the question is trivial, I think it requires specialist attention!
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    Quote Originally Posted by CSMYTH3025
    After 162 views and no replies I'm wondering if my question is so trivial as to not even warrant a reply or so perplexing that no reply is posible.

    Where's DrRocket when you need him?

    Chris
    I don't know enough about the Lens-Thirring effect to comment. However, if I were given the choice of betting on the computational accuracy of several experts vs one amateur, I'd take the side of the experts.
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  10. #9  
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by CSMYTH3025
    After 162 views and no replies I'm wondering if my question is so trivial as to not even warrant a reply or so perplexing that no reply is posible.

    Where's DrRocket when you need him?

    Chris
    I don't know enough about the Lens-Thirring effect to comment. However, if I were given the choice of betting on the computational accuracy of several experts vs one amateur, I'd take the side of the experts.
    ...And right you would be to do so...

    In my search to figure out why my calculation doesn't seem to be coming out right I ran across a thing called the "two body" problem. (ref. http://en.wikipedia.org/wiki/Two-body_problem )

    The math in this Wikipedia article is beyond my ability to decipher, but I am able to figure out that I need to use the reduced mass of these pulsars to make my calculation. This turns out to be 1.285x10^30 kg.
    (ref. http://www.wolframalpha.com/input/?i...E30+kg&x=2&y=8 )

    Any help on how to apply the equations given in the wikipedia article to the orbital separation and the orbital period of these pulsars would be greatly appreciated.

    Chris
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  11. #10  
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    As it turns out, another source directed me to a paper which cites a more exact figure for the separation of these pulsars: 2.9 lt-s (B.B.P. Perera, et al - arXiv:1008.1097). This value (~869,000 km) produces an orital period very close to the 2.4 hr orbital period cited in the same and other papers.

    Henceforth I'll be a bit more skeptical about the numbers I read in popular science articles.

    Thanks
    Chris
    It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow.
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