2
$\begingroup$

Now that we know that gravity waves exist, we can consider to design a new unit of measurement, i.e. deciGravs (from dB) and we can predict what the backround noise of dG's is locally and in space.

Consider a theoretical high-res LIGO that can graph gravity waves here and far away, we can ffwd the record to represent the dG's at human timeframes.

What are the loudest local waves? Can we see the moon as the loudest local wave, followed by other planets and moons, are local bodies much louder than local bh waves?

There is an expected 3D wave map type locally and in deep space that we can model with graphical animations? Can we draw it easily in 2D/3Dusing 5 lines of code for every body and lots of processing?

Perhaps it makes sense to define a frequency chart of dG's and astroHz and a bit like the electromagnetic waves, and chart gravity-waves, amplitude and frequency trends and types?

Perhaps supernovas and solar flares and many background waves appear on graviCharts. Can we know what graviCharts and backround noise of gravity resembles here and far away?

$\endgroup$
1
$\begingroup$

For orbiting objects, gravitational wave intensity depends on the second time derivative of the quadrupole moment of an isolated system's stress–energy tensor (which for the wimpy objects in our vicinity is proportional to the mass times the line of sight acceleration) and drop off with the distance. So you can easily estimate the GW intensity of any object. Hint: It's small for nearby objects.

As requested, I have tried to estimate the GW amplitude and I found the numbers somewhat surprising. I looked at the Moon, Jupiter, Io, the LIGO neutron star and a pair of supermassive BHs if they were at the Galactic center.

I got the mass of each object in Suns, the orbital radius in miles, the orbital period in years and the distance in AU. The angular acceleration is computed as r * omega2. Multiply by mass to get GW radiation at source. Divide by distance to get GW amplitude observed at Earth. (All units relative and arbitrary.)

Object             Acceleration   Mass*Acceleration  Est. amplitude
Moon               3 x 10**7      1                  4 x 10**2
Jupiter            3 x 10**6      3 x 10**3          7 x 10**2
Io                 1 x 10**10     5 x 10**2          1 x 10**2
LIGO Neutron star  1 x 10**19     3 x 10**16         4 x 10**6
Supermassive BHs   1 s 10**9      2 x 10**15         3 x 10**6

(The supermassive BH numbers are really quite arbitrary, since you can assume any separation you like and pretty much any mass. I picked 1 AU and 1,000,000 suns mass. You can easily get much larger numbers, but the frequency will typically be too low to be seen by LIGO.)

The other really important thing to remember is that in spite of Io being about as bright as the sources LIGO has observed, the frequency of Io's radiation is about 10-5 Hz. LIGO is only really sensitive in the 10-1000Hz range and has no chance at all of ever seeing IO or Jupiter or the Moon or even a pair of supermassive BHs that are not in the last milliseconds of merger. If eLISA gets built, it can probably see at least some supermassivs BH pairs.

|improve this answer|||||
$\endgroup$
  • 1
    $\begingroup$ GW detectors are sensitive to wave amplitude which falls as the reciprocal of distance. $\endgroup$ – Rob Jeffries Jun 5 '18 at 13:39
  • $\begingroup$ small and wimpy are kind of vague terms in this context: I know there is a widespread confusion (that appears to be reflected in this question) that things like tides are caused by gravity waves from the sun and the moon. This answer might clear that up with more finality if someone that could do the math compared the wave amplitudes. $\endgroup$ – antlersoft Jun 5 '18 at 15:24
  • $\begingroup$ @antlersoft, unless you're referring to wimps en.wikipedia.org/wiki/Weakly-interacting_massive_particles $\endgroup$ – Carl Witthoft Jun 5 '18 at 17:38
  • $\begingroup$ That gives a very deep idea of gravity wave topology, i'm surprised that the moon doesn't provide the highest amplitude waves, if the moon is at the zenith or the antizenith, it would generate the loudest waves. Perhaps a gravity interferometer would have to be a different size to see that kind of wavelength, like a radio antenna? $\endgroup$ – com.prehensible Jun 5 '18 at 18:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.