A question on Gravity Waves and Gravity Radiation

[Tanelorn]

Relativity predicts that the binary system will lose energy with time as orbital energy is converted to gravitational radiation. In 1983, Taylor and collaborators reported that there was a systematic shift in the observed time of periastron relative to that expected if the orbital separation remained constant. In the diagram shown here, data taken in the first decade after the discovery showed a decrease in the orbital period as reported by Taylor and his colleagues of about 76 millionths of a second per year. By 1982, the pulsar was arriving at its periastron more than a second earlier than would have been expected if the orbit had remained constant since 1974.


http://www.astro.cornell.edu/academics/courses/astro201/psr1913.htm


Does Relativity estimate or predict the frequency of the gravitational radiation?
Can we also estimate the amount of gravitational radiation being emitted and thus the amount present at a gravity wave detector here on earth?
Are there any other causes which might explain the loss of orbital energy?

 

[Janus]

Relativity predicts that the binary system will lose energy with time as orbital energy is converted to gravitational radiation. In 1983, Taylor and collaborators reported that there was a systematic shift in the observed time of periastron relative to that expected if the orbital separation remained constant. In the diagram shown here, data taken in the first decade after the discovery showed a decrease in the orbital period as reported by Taylor and his colleagues of about 76 millionths of a second per year. By 1982, the pulsar was arriving at its periastron more than a second earlier than would have been expected if the orbit had remained constant since 1974.


http://www.astro.cornell.edu/academics/courses/astro201/psr1913.htmDoes Relativity estimate or predict the frequency of the gravitational radiation?

The frequency would be twice the frequency of the rotational period.

Can we also estimate the amount of gravitational radiation being emitted and thus the amount present at a gravity wave detector here on earth?

The power could be found by:

P =\frac{32}{5}\frac{G^4(M_1M_2)^2(M_1+M_2)}{c^2 r^5}

Which works out to about 3.9e22 Joules/sec.

It is 21,000 ly away, so we would get something like 3.14e-19 Joules/sec per square meter. here on Earth.

Are there any other causes which might explain the loss of orbital energy?

I'm not gong to say that it is impossible, but the loss seen fits what is predicted by GR, so it would have to be a pretty large coincidence for another mechanism to match that exact energy loss.

 

[Tanelorn]

Thanks Janus for an excellent reply.

The frequency of the gravitational radiation then is just related to the frequency at which the gravitation field is changing due to the period of the binary orbit. I expected this, but didnt want to assume anything. So gravity waves are nothing more than variation with time of the static gravitational field?

I understand that gravity wave detectors have been built deep underground to prove gravity waves exist. Would we expect to be able to detect this level of gravitational radiation here on Earth with the sensitivity of our detectors and with the level of noise and interference here and elsewhere?

 

[Eyelegal]

So far I don't think they have had any luck with gravity waves. Some have been searching for up to 20 years or more? Hopefully its about sensitivity and not a lack of the thing they are looking for. That would mess things up a little...