Would it be possible to transmit information through gravitational waves?

First thing I've been wondering is how the gravitational field is emitted. Matter emits gravitational waves, and I guess that those waves travel at around the speed of light. If that's not the case, please direct me to something that explains that.
For now I'll assume that this emits a waves that travels at the speed of light.

Now those waves are emitted constantly without the apparent need of energy. Just the mass being there is enough to emit those waves, and the mass itself isn't consumed by the emission of gravitational waves. Again that's my assumption, please tell me if I'm wrong.

Now if we would be able to modulate the mass of an object, we would be able to modulate the gravitational waves this object emits. Hence we would be able to transmit information through those waves, if of course we'd have a device that detects gravitational waves with enough sensitivity.

Those waves would be transmitted at no cost, because the waves are emitted by the mass. The only cost of this transmission would be the "mass modulator", which has yet to be invented and which would require energy. However the actual transmission doesn't require energy, and the gravitational waves are harmless, unlike the EM ones.

So here comes my question (as in the title): would it be possible somehow to use the gravitational waves to transmit information?

Answer

First it's important to note that gravitational waves do require energy to produce. A good example of this is a binary pulsar, where the emission of gravitational waves carries energy away so the two pulsars spiral in towards each other and will eventually merge.

Having said this, it is theoretically possible to modulate a gravitational wave and use it to transmit information. You don't need a mass modulator, you just need something with a changing quadropole moment - the simplest example of this is a spinning dumbbell, and indeed this is basically what the binary pulsar system is. If you can change the rotation frequency you can frequency modulate the gravitational wave.

However gravitational waves are exceedingly hard to generate in the sense that very little of the energy of your system is carried away as gravitational waves. It doesn't seem likely we'll ever use gravitational waves for transmitting information.