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B Gravitational Waves prediction

  1. Feb 19, 2016 #1
    Dear Friends!
    Q.There was no direct evidence of binary black holes till September 14,2015,when signals coming from about 1.3 billion light years away were captured by LIGO.
    Now my question is that how in advance we knew about the specific colliding pair.Did we theoretically predict the graph (between what values?)and did the real graph matched to a high degree with predicted graph.
     
  2. jcsd
  3. Feb 19, 2016 #2
    Most likely there were indirect observations; there seem to be a lot of different models.

    "The first way we detect black holes is by their gravitational influence. For example, at the center of the Milky Way , we see an empty spot where all of the stars are circling around as if they were orbiting a really dense mass. That's where the black hole is.

    "The second way is by observing the matter falling into the black hole. As matter falls in, it settles in a disk around the black hole that can get very hot. Some of the energy liberated from falling in is turned into light, which we can then see, for example, in X-rays.

    http://chandra.harvard.edu/blog/node/308

    The article, https://en.wikipedia.org/wiki/Binary_black_hole has some interesting background. Note comments about portions of different models may be used in unison. The title references at the bottom of the article also offer some insights and opportunities for additional details.

    Seems like the question now may be, which model was the best fit and was that luck or skill??
     
  4. Feb 19, 2016 #3

    phyzguy

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    Before observing the GW pulse on Sept 14, we didn't know that the specific BH pair that collided even existed, let alone its properties. Theoretical studies had been done of neutron star-neutron star, neutron star-black hole and black hole-black hole coalescence, and we had simulations of what the GW waveforms for these events would look like. To determine what type of event produced the observed GW pulse, the analysis team ran ~250,000 simulations of different types of events and the reported collision of 2 BHs fit the observations the best. The fit between the observations and the measurements is quite good. If you look at the second panel down in Figure 1 of this paper, you will see the comparison of the measurements to the simulations.
     
  5. Mar 8, 2016 #4
    Please tell me, if you know, the angle between the orbital plane of the merging black holes and a line that connects Earth with the centre of mass of the 2 BHs. I searched the internet few days and didn't find any information about it.
     
  6. Mar 8, 2016 #5

    phyzguy

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    I think if you look at Figure 2 from this paper, it will answer your question. The best fit shows the angle between the line of sight and the angular momentum vector of the system is about 150 degrees. An angle of 180 degrees would mean that the plane of the orbit is perpendicular to the line of sight, so the orbit is(was) tilted by about 30 degrees relative to a plane perpendicular to the line of sight.
     
  7. Mar 9, 2016 #6
    Thank you!
     
  8. Mar 11, 2016 #7
    Thank you friends!
    I could not see the figures you mentioned .
    My further question is :
    As I studied in EM waves an accelerated charge creates waves and they propagate in space pushing each other (Electric component and perpendicular magnetic component ) and the field generates wave pulse which has momentum and energy.We can also detect it through LC circuit.
    Now a gravitational wave is produced by accelerated mass. There is only one field component in it.How it propagates?Do we have results parallel to EM waves like Poynting vector and other well known results of EM waves E equal to (B)c etc.
    I am not expert.So please correct me if my question has drawbacks.
    Thanks!
     
  9. Mar 11, 2016 #8

    phyzguy

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    This isn't really correct. The Electromagnetic field is a rank 2 antisymmetric tensor, which has 6 components. Splitting into E and B parts with three components each is a somewhat arbitrary split which is observer dependent. The gravitational field is represented by the metric tensor, which is a rank 2 symmetric tensor with 10 components, so it has more complexity than the EM field, not less. Both propagate through empty space because the field equations that they satisfy have wavelike solutions.
     
  10. Mar 12, 2016 #9
    Thank you so much "phyzguy". Your guideline was very much needed.Hope you will continue to guide.This helps me to understand Physics faster.
     
  11. Mar 12, 2016 #10

    phyzguy

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    You're welcome. Why could you not see the figures I linked to? Arxiv is an open web site, so you should be able to see the papers. What went wrong?
     
  12. Mar 12, 2016 #11
    I was using Nokia Lumia 720 .Hopefully I ca. see it in laptop soon.Thankyou for your concern.Will respond after careful study.
     
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