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B Gravitational wave signal duration

  1. Oct 12, 2016 #1
    I have a question about why the duration of the gravitational wave signal detected by LIGO was 0.25 seconds or so. I think I understand correctly that as the two binary black holes rotate around each other and move closer together there is a loss of angular momentum that is converted to gravitational waves of a certain frequency. The generation of gravitational waves would then end upon the merging of the two black holes. My questions are: is the frequency of the gravitation wave constant throughout the entire history of the black hole merger? Is this frequency red-shifted in the gravitational wave’s journey from its source to the LIGO instrument due to the expansion of the universe? Why is the duration of the signal 0.25 seconds?
     
  2. jcsd
  3. Oct 12, 2016 #2

    Jonathan Scott

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    The frequency rapidly increased as the objects moved closer together. It would be redshifted. It started once the objects got close enough that their gravitational waves became sufficiently energetic to be detectable at this distance, and stopped once the objects merged and settled into a single spinning object.

    For more information and links to other sources, see this Wikipedia entry:
    https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves
     
  4. Oct 12, 2016 #3
    So the quantum wave frequency over the duration of the pulse detected by LIGO increase over its 0.25 duration?
    So the frequency of the gravitational wave increases during the approximately 0.25 second duration of the signal being detected by LIGO?
     
  5. Oct 12, 2016 #4

    Jonathan Scott

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    There's nothing quantum about it. The energy of a gravitational wave increases rapidly as the objects get closer (so the gravity is stronger and the rate of change is much faster).

    Yes, I just said that. You can see a graph of the wave as observed at each detector and the corresponding theoretical prediction in the Wikipedia entry.
     
  6. Oct 12, 2016 #5
    Got it. I very much appreciate your responses to my questions.
     
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