Question: Guran’s [comment](https://worldbuilding.stackexchange.com/a/60304/885)

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> Perhaps they are tinkering with the solar activity, turning stars into Yotta-watt, nano-bit/second beakons. (We would see the pattern eventually, but not before we looked at century-spanning data)
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makes me think of [astroseismology](https://en.wikipedia.org/wiki/Asteroseismology) which is a newly available field of study since new instruments can resolve this for stars [beyond our sun](https://en.wikipedia.org/wiki/Helioseismology).

![star vibrations](https://upload.wikimedia.org/wikipedia/commons/e/ec/Helioseismology_pmode1.png)

Rather than building huge power-hungry transmitters, how could an advanced civilization induce and modulate vibrations in their star that could be observed at interstellar distances but are the most miserly in energy consumption to cause?

Answer: 
[Muon-catalyzed fusion](https://en.wikipedia.org/wiki/Muon-catalyzed_fusion)

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> ... each muon can only catalyze at most a few hundred deuterium tritium nuclear fusion reactions
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Maybe Inject streams of Muon's in to Sun, it will spedup burning probably for any thermonuclear reaction, and for p-process it may be more efficient as proton have only 1e charge.

This way a Star will be amplifier for your signal, and by focusing beams you may create any distribution of energy and modulate it over time as you wish. Penetration will be maybe up to the star core.

So muon beams get you possibility to use less and get more and have any distribution in outer layers of the star.
Find a neutron star, turn it into an x-ray pulsar
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First off, no one is going to cause vibrations detectable at light years distance to their own star. Assuming they want their home planet (circling said star) to be habitable, they aren't going to put their planet through a freeze/fry cycle.

[X-ray pulsars](https://en.wikipedia.org/wiki/X-ray_pulsar) release the potential energy of accreted gasses falling to the surface of the (neutron) star giving a continuous x-ray release. As long as the neutron star is spinning with its magnetic axis (where the gas falls) tilted with respect to its spin axis, then anyone looking at the start will see the cyclic appearance and disappearance of of the x-ray beams.

To make this happen, you want to modulate the spin of the pulsar to what you desire. You can do this by accreting mass to the neutron star, which can either increase or reduce angular momentum. The best candidate for accretion mass for modulating and powering your pulsar would be another star, but I suppose a Jupiter or Super-Jupiter would work, just not for as long of a time.

Sure moving a Jupiter (or a star) to a Neutron star isn't the least energy intensive thing you can think of, but it is probably the least energy intensive way to make a galactic scale cyclic transmitter.