NumberlineA Posted October 30, 2018 Share Posted October 30, 2018 How did LIGO determine the mass of distant black hole mergers? LIGO found the direction to the merger from the time difference of the two detectors and from the polarization of the gravitational waves. Was the gravitational wave that was detected a combination of more then one gravitational wave? Link to comment Share on other sites More sharing options...
Strange Posted October 30, 2018 Share Posted October 30, 2018 5 hours ago, NumberlineA said: How did LIGO determine the mass of distant black hole mergers? They match the received waveforms against simulations of what would be generated by various combinations of black holes sizes. They start of by using a set of templates corresponding to different types of events (two black holes, two black holes of different sizes, two neutron stars, a neutron star and a back hole, and so on). These are used to identify possible signals (the gravitational waves are so small, that signals are not much larger than the background noise). Then they run a series of simulations to find the exact mass, angular momentum, orientation, etc. Not sure how much detail you want to get into, but this web page has all the papers from the first detect along with a brief summary, a more detailed description and a link to the paper itself. The papers are quite mathematical but some can be read without following all the math. https://cplberry.com/2016/02/23/gw150914-the-papers/ Link to comment Share on other sites More sharing options...
NumberlineA Posted October 30, 2018 Author Share Posted October 30, 2018 For planet detection the change in the red shift of light tell the wobble in the star. Then Newton's modification of Kepler's Third Law gives the mass. Link to comment Share on other sites More sharing options...
Strange Posted October 30, 2018 Share Posted October 30, 2018 17 minutes ago, NumberlineA said: For planet detection the change in the red shift of light tell the wobble in the star. Then Newton's modification of Kepler's Third Law gives the mass. Detecting exoplanets and calculations using Newtonian gravity are much simpler than estimating the source of gravitational waves. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 Relativity says that gravitational waves must red shift. Red shift is the only way to determine the mass of the black hole merger. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 6 hours ago, NumberlineA said: Relativity says that gravitational waves must red shift. Red shift is the only way to determine the mass of the black hole merger. Red shift depends on distance, not mass. The characteristics of the “chirp” (frequency, shape of pulse, etc) indicate the mass. Ah, I see (sorry for being slow), you are making an analogy between the detection of black holes and exoplanets? They are completely different. In the case of exoplanets, we have continuous observations of a star and can look for small changes. (I don't think red-shift is used, but changes in brightness: https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets) In the case of black hole mergers, there is no signal until the last few seconds when gravity waves become large enough to be detected. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 Varying red shift is from motion to and fro which is the decaying orbit of the black hole which can be used to find the mass. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 That is not how gravitational waves are generated or detected. That is not how the mass is determined. Read the link I provided. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 Changing red shift is changing frequency, is changing wave length, and is changing energy of the gravitational wave. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 11 minutes ago, NumberlineA said: Changing red shift is changing frequency, is changing wave length, and is changing energy of the gravitational wave. Sigh. The only way red-shift is relevant to gravitational waves is for determining the distance (from Hubble’s law). Link to comment Share on other sites More sharing options...
swansont Posted November 2, 2018 Share Posted November 2, 2018 1 hour ago, NumberlineA said: Varying red shift is from motion to and fro which is the decaying orbit of the black hole which can be used to find the mass. Since you don't know what the reference frequency is, I would think redshift is not very useful. You can only tell what the shift is when you know what the frequency is for a system at rest, such as with spectral lines. The gravitational wave chirp was not described as a redshift in anything I can recall reading. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 The wave is red shift when the emitting object is go away from you. The wave is blue shifted when the object is coming towards you. Make your base in between. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 5 minutes ago, NumberlineA said: The wave is red shift when the emitting object is go away from you. The wave is blue shifted when the object is coming towards you. Make your base in between. In the case of gravitational waves there is no means for measuring the redshift due to the orbits. That is because the change in redshift happens at the same frequency as the gravitational waves. And the frequency is constantly changing. And the redshift due to the orbits would be immeasurably small. And ... stop just making stuff up. This is not how it works. I suppose the redshift caused by the orbits could produce a slight asymmetry in the waveform. But I have never seen any mention of this. Which isn’t surprising, it would be included (implicitly) in any simulation done to determine the expected waveform. So it wouldn’t provide any extra information. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 Near a Black Hole the speeds are enormous and so also the red shifts. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 3 minutes ago, NumberlineA said: Near a Black Hole the speeds are enormous and so also the red shifts. Please provide some data or calculations to support that. Or evidence that it is relevant to the detection of gravitational waves. Link to comment Share on other sites More sharing options...
NumberlineA Posted November 2, 2018 Author Share Posted November 2, 2018 A black hole with the mass of thirty billion suns has some wicked smart gravity. Gravity causes acceleration. Link to comment Share on other sites More sharing options...
Strange Posted November 2, 2018 Share Posted November 2, 2018 1 minute ago, NumberlineA said: A black hole with the mass of thirty billion suns has some wicked smart gravity. Gravity causes acceleration. So you can’t provide any support for your claims. Shall we just close this thread. Link to comment Share on other sites More sharing options...
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