[katieHaylor (OP)]

Patrick asks:

Do gravitational waves *only* appear when massive objects collide? Or do
we create really tiny waves all the time as we move about?

Can you help?

[jeffreyH]

Any object with mass that accelerates will radiate gravitational waves. This includes all objects in orbit. That is a lot of gravitational radiation. This is not easily detected since gravity is weak. It takes a lot of mass and a lot of acceleration for the waves to become detectable. Hence why neutron star and black hole mergers were detected.

[Bill S]

Any object with mass that accelerates will radiate gravitational waves.

Presumably E=mc^2 would imply that this would also be the case for moving energy, so gravitational waves' could radiate more gravitational waves? 

[jeffreyH]

Hmmmm... Interesting thought.

[Kryptid]

Any object with mass that accelerates will radiate gravitational waves. This includes all objects in orbit. That is a lot of gravitational radiation. This is not easily detected since gravity is weak. It takes a lot of mass and a lot of acceleration for the waves to become detectable. Hence why neutron star and black hole mergers were detected.

I've read that it needs to be a gravitational quadrupole specifically (i.e. a perfect sphere will not radiate gravitational waves). I don't know for sure if that's true or not. It was a long time ago when I read it.

[evan_au]

do we create really tiny gravitational waves all the time as we move about?

Yes.
The Earth orbiting the Sun radiates about 200W of gravitational waves - much less energy than your car engine emits while idling. With current techniques we have no way to detect such low power gravitational waves.

Humans walking, or Newton's apple falling under Earth's gravitational attraction radiates far less energy again.

LIGO & VIRGO are continually struggling with vibrations from earthquakes, thermal vibrations of atoms in the mirrors, and phase noise in their lasers - this makes it hard to measure the tiny vibrations caused by gravitational waves.

But even then, there is probably a considerable background noise of gravitational waves from multiple spiraling neutron stars and black holes that are individually too small to extract from the noise until they get into their final, dramatic, last few seconds. Plus one-off impulses from supernova and starquakes that don't have the telltale chirp signal of merging binaries. In addition to events that are at too low frequency for LIGO (<50Hz, like orbiting supermassive black holes) or too high frequency for LIGO (> 1kHz, like asymmetrical millisecond pulsars).

If and when LISA, the space-based gravitational wave detector becomes operational, we should be able to detect more of these events (especially the low-frequency ones) with much greater sensitivity. Perhaps even detecting multiple different binary systems long before they actually merge.

See: https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna

[jeffreyH]

But if the hypothetical graviton is anything like the gluon then it can emit or absorb gravitons. So in this case the energy is in the particle and depends upon wavelength. Not that you would be able to detect such a small increase in energy.

[evan_au]

I've read that it needs to be a gravitational quadrupole

If two equal masses are rotating around each other 100 times per second, the radiated gravitational waves have a frequency of 200Hz.

On the other hand, if you had positive and negative charges of equal magnitude  (a dipole) rotating around each other 100 times per second, the radiated electromagnetic waves would have a frequency of only 100Hz.

See: https://en.wikipedia.org/wiki/Quadrupole#Gravitational_quadrupole

[yor_on]

You're correct Kryptid,  you usually are :)

https://van.physics.illinois.edu/qa/listing.php?id=204