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Einstein@Home search for periodic gravitational waves in LIGO S4 data

  1. Apr 11, 2008 #1

    wolram

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    arXiv:0804.1747 [pdf, other]
    Title: The Einstein@Home search for periodic gravitational waves in LIGO S4 data
    Authors: LIGO Scientific Collaboration: B. Abbott, et al
    Comments: 29 pages, 19 figures
    Subjects: General Relativity and Quantum Cosmology (gr-qc)
    A search for periodic gravitational waves, from sources such as isolated rapidly-spinning neutron stars, was carried out using 510 hours of data from the fourth LIGO science run (S4). The search was for quasi-monochromatic waves in the frequency range from 50 Hz to 1500 Hz, with a linear frequency drift f-dot (measured at the solar system barycenter) in the range -f/tau < f-dot < 0.1 f/tau, where the minimum spin-down age tau was 1000 years for signals below 300 Hz and 10000 years above 300 Hz. The main computational work of the search was distributed over approximately 100000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 hours, despite the large parameter space searched. No statistically significant signals were found. The sensitivity of the search is estimated, along with the fraction of parameter space that was vetoed because of contamination by instrumental artifacts. In the 100 Hz to 200 Hz band, more than 90% of sources with dimensionless gravitational wave strain amplitude greater than 1e-23 would have been detected.
    Could some one tell me what type of event equates to the last sentence please.
     
  2. jcsd
  3. Apr 12, 2008 #2

    wolram

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    Am i in the bad book or is it that no one knows?
     
  4. Apr 19, 2008 #3

    Redbelly98

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    Hello wolram, I joined the forum within the last week and just came across your post.

    As I understand it, the events expected to give rise to detectable gravitational waves involve supernovas, neutron stars, or black holes. In other words, really massive and energetic astronomical objects. I don't know the specifics beyond that.

    It's funny, I first heard about this project in the late 1980's. Now almost 20 years later it is still going. Would be nice if they could detect something.
     
  5. Apr 19, 2008 #4

    jimgraber

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    isolated rapidly-spinning neutron stars
     
  6. Apr 19, 2008 #5

    jimgraber

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    In more detail, you want neutron stars spinning 50 to 100 times a second, with a mountain range or something else to give them a quadrupole moment. You also want them to be as near as possible. The reason for this frequency range is that it is where current LIGO is most sensitive. But most grav wave people expect binaries to be detected first, since their quadrupole moments are so much larger. But they need to check everything plausible, and they are.
    Best,
    Jim Graber
     
  7. Apr 20, 2008 #6

    LURCH

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    Isn't it impossible for a neutron star to have a mountain range? In all models of which I'm aware, neutron stars are the smoothest objects in universe, with the possible exception of Quark stars if they are proven to exist. I think the waves being spoken of refer to two neutron stars orbiting one another.
     
  8. Apr 20, 2008 #7

    jimgraber

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    yes, plausible "mountain ranges" on neutron stars are very small, millimeters at best.
    (Owen astro-ph/0503399 gives a maximum ellipticity of a few times 10^-7, which works out to a few millimeters for a 10 km neutron star.)
    That is why the GW signal is so small.
     
  9. Apr 20, 2008 #8

    wolram

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    So how long will it be before some one submits a paper as to why we do not see GRs
     
  10. Apr 20, 2008 #9

    turbo

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    Woolie, it may be a LONG time because because gravitational waves are a figment of the the intersection of classical (Newtonian) physics with relativistic physics. Einstein insisted later that gravitation is an entirely local, emergent force. If he was right, the existence and propagation of gravitational waves is either non-existent or highly localized.
     
  11. Apr 20, 2008 #10

    wolram

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    So all these fantastical new observation methods are just bunkum.
     
  12. Apr 20, 2008 #11

    turbo

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    If Einstein's ideas post 1920 are correct, yes.
     
  13. Apr 20, 2008 #12
    I really dont think so, we have this Hulse-Taylor binary and its loosing energy with a rate that is in very good consistency with the calculations how much energy should be emitted by grav. waves (if it was a higly localized effect then the binary system should not emitt waves/energy or did I misunderstand your point ?). we do not have direct evidence yet, thats why we build this detectors, but Hulse-Taylor is very good indirect evidence.
     
  14. Apr 21, 2008 #13

    jimgraber

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    Hi wolram,
    As I said above it won't be rotating neutron stars but binaries.
    If they (gravitational waves) are not seen in the first year after advanced LIGO goes operational, there will be a lot of people scratching their heads and papers like the above will start to appear.
    Based on current schedules,
    (see http://www.ligo.caltech.edu/advLIGO/scripts/summary.shtml )
    advanced LIGO is due to be operational by the end of 2013,
    so this could happen around 2014-2015.
    But I'm betting the other way, and expecting detection papers instead of non-detection papers in that time frame.
    Best,
    Jim Graber
     
    Last edited: Apr 21, 2008
  15. Apr 21, 2008 #14

    I live right down the way from this, about 30 minutes, hoping to take a tour of it soon

    http://www.ligo-wa.caltech.edu/
     
  16. Apr 21, 2008 #15

    Wallace

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    The spin-down rate of pulsars has already been observed to be precisely what would be expected if GW's were radiating energy away from the pulsar. If you assume GR but no GW's then you don't get the right answer. I'd say this is a good piece of evidence for the existence of GW already, but of course nothing beats direct detection.
     
  17. Apr 21, 2008 #16
    I was trying to make a similar point in my post above, just talking about the Hulse-Taylor binary. because I thought that this binary did provide the most precise confirmation yet. but I had this information in the back of my mind for more than a decade. so now there are measurements of pulsars that are more precise (in terms of energy loss) than Hulse-Taylor ?
     
  18. Apr 21, 2008 #17

    Wallace

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    Sorry I missed your post about that. To answer your question, yes there are many binary pulsars now known that have spin down rates that are accurately predicted by GR (including Gravitational Waves).
     
  19. Jun 16, 2008 #18

    LowlyPion

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    In addition to LIGO there is also LISA.

    http://lisa.jpl.nasa.gov/gallery/ligo-lisa.html

    I understand they have spent $290M so far on these 4 km LIGO interferometers in WA and LA and who knows how much for LISA is required.

    LISA is intriguing to me insofar as they can get a 5x10^9m interferometer properly working and calibrated to measure 10^-12 of space disturbance over that distance down to 1hz. ("Can you hear me now?")
     
  20. Jun 20, 2008 #19

    LowlyPion

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    The more I read about LIGO the more likely it seems to me to be a bust.

    "This is also the first time we've been able to estimate the role played by gravitational waves in the slowing down of a neutron star and is an important stepping stone on the way to actually detecting gravitational waves."
    http://www.interactions.org/cms/?pid=1026276

    It goes on to say that because they don't detect gravitational distortions then the neutron star must be perfectly spherical? A good conclusion no doubt, if in fact the LIGO was detecting distortion waves from any source, but rather a sketchy conclusion in the absence of any other observational successes with gravity waves.

    Or is it that I have missed reports of actual detections reported elsewhere?
     
  21. Jun 20, 2008 #20

    jimgraber

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    Hi, LowlyPion,
    It's true that as of now LIGO has not seen anything exciting or even set really unexpected upper limits. But within the next three to five years they expect to see things. If they still don't see anything in five years (and the machine doesn't really go bust--not expected), then that will be a big surprise.
    Jim Graber
     
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