Could Fast Radio Bursts Be Powering Alien Probes?

[KelvinZero]

Both the Dyson sphere and matrioshka brain radiate with the same luminosity as the star they draw energy from.  The luminosity is low temperature emission. 

Yep.. that was sort of my point. There are plenty of good ideas but then we must go and look for the objections. It is likely the idea has been kicked back and forth a few times and people have found ways to explore it using basic principles.

[high road]

... wondered if most of the universe is hidden away in dark "matrioshka brain" like objects. Could be Dyson spheres....

Both the Dyson sphere and matrioshka brain radiate with the same luminosity as the star they draw energy from.  The luminosity is low temperature emission. 

Maybe something like this:  ll pegasi

Sure, the luminosity is the same, but considering the re-emitted flux is much lower due to the bigger surface area, wouldn't a star with a partial Dyson Swarm/Matrioshka Brain/... appear to us as a smaller and/or colder star that is somehow much heavier than it seems to be based on its apparent luminosity? Isn't the star's brightness our main indicator of its size? So how would we know our formula to calculate their size is influenced by such phenomena unless we see large differences between the sizes we think they are and the gravity they appear to have? (which happens to be the case)

A good example is four 15 watt florescent bulbs, a 60 watt incandescent bulb, and an electric heater using 60 watts.  Normal human reaction is to say that the florescent bulbs are much "brighter" and that the electric heater is not a light.  The bolometric luminosity is the same for each item (assuming we ignore convection or add watts to compensate).  The visual luminosity of the florescent is much higher.  In parts of the infrared the incandescent has highest luminosity.  In microwave frequency the heater is much "brighter".

 

So how would we know wether we're looking at a red (super)giant or a main sequence star of the same luminosity surrounded by a radiator Dyson swarm approaching the density of a full Dyson sphere?

My instinct is that variable coverage is more likely in a partial sphere.  As coverage varies from 1% to 20% the visual part of the star's spectrum would vary between 80 and 99% visual luminosity.  The far infra-red spectrum would also vary but not necessarily synchronized with the visual variability.  The radiators could be on multiple surfaces.  Is possible that most would radiate heat away from the star so far infra-red would vary inverse to visual. 

A partial dyson sphere acting as a Shkadov thruster would have less infra red (compared to stationary) if it was moving towards us or perpendicular.  If they are moving away from us the infra red luminosity would be much higher.  Mirrors could create strange stars with higher visual luminosity too but doubling is unlikely. 

Orbiting mirrors and radiators also red and blue shift as they move. 

All stars are a point of light in our telescopes.

As far as measuring diameters is concerned, all stars are badly resolved blobs of light surrounded by diffraction patterns in our telescopes.

Incomplete Dyson swarms with individual elements between the size of NYC and Luna, assuming there's an upper limit to their practical size, would not be detectable by our current or upcoming telescopes. We would assume the star is just somewhat more variable. The movement and reflected radiation of the individual elements is not enough to be detectable as an individual space station/planetary body. The scattering effect they have on the radiation emitted by the star might be actively filtered away to resolve the star better.

And all this still assumes that ETI somehow doesn't come to the conclusion that at a certain scale, rather than using the radiation emitted by natural fusion reactors, it's far more practical to just do the fusion in not-so-natural fusion reactors and become independent of stars in the first place.

With 84% of all matter unaccounted for by our measurement of star sizes, and our telescopes having a limited capability to pick up such artificial fusion reactors emitting about as much energy as a brown dwarf, there's plenty of room to hide in plain sight.

[as58]

So how would we know wether we're looking at a red (super)giant or a main sequence star of the same luminosity surrounded by a radiator Dyson swarm approaching the density of a full Dyson sphere?

Their spectra would be completely different.

[stefan r]

So how would we know wether we're looking at a red (super)giant or a main sequence star of the same luminosity surrounded by a radiator Dyson swarm approaching the density of a full Dyson sphere?

Their spectra would be completely different.

A red giant should have a mostly hydrogen spectra.  The Dyson sphere would have characteristic spectrum from whatever material was radiating.  For example, an aquarium would have water emissions and glass emissions.  The glass also blocks some frequencies.  If the Aliens use cast iron radiators then we would detect lots of iron.  If they paint the radiators with exterior house paint there will be TiO₂ emission.   

Astronomers determine rotational velocity by looking at the red and blue shifts.  A typical Dyson swarm is likely to be rotating at orbital velocity.  That would not be a stable situation for a gas.  The Dyson swarm can orbit in perpendicular directions.  Stars rotate on one axis. 

I am not sure if graphene and carbon nanotubes would be identified as carbon dust (soot).  If I was publishing the data I would just state the molecular structures and not mention the construction possibilities.

For many stars that are inside of dust clouds we cannot determine whether it is a Dyson sphere.

[as58]

So how would we know wether we're looking at a red (super)giant or a main sequence star of the same luminosity surrounded by a radiator Dyson swarm approaching the density of a full Dyson sphere?

Their spectra would be completely different.

A red giant should have a mostly hydrogen spectra.  The Dyson sphere would have characteristic spectrum from whatever material was radiating.  For example, an aquarium would have water emissions and glass emissions.  The glass also blocks some frequencies.  If the Aliens use cast iron radiators then we would detect lots of iron.  If they paint the radiators with exterior house paint there will be TiO₂ emission.   

It's not that simple, for example a cool star like a red giant does not (usually) show any hydrogen lines and a (macroscopic ) iron object would just radiate more or less like a black body.

[high road]

Excellent replies, all of them.

Population density and/or not developing fusion reactors remain the biggest assumptions.

[stefan r]

So how would we know wether we're looking at a red (super)giant or a main sequence star of the same luminosity surrounded by a radiator Dyson swarm approaching the density of a full Dyson sphere?

Their spectra would be completely different.

A red giant should have a mostly hydrogen spectra.  The Dyson sphere would have characteristic spectrum from whatever material was radiating.  For example, an aquarium would have water emissions and glass emissions.  The glass also blocks some frequencies.  If the Aliens use cast iron radiators then we would detect lots of iron.  If they paint the radiators with exterior house paint there will be TiO₂ emission.   

It's not that simple, for example a cool star like a red giant does not (usually) show any hydrogen lines and a (macroscopic ) iron object would just radiate more or less like a black body.

Hydrogen has Humphrey lines.  Should be peak intensity near room temperature.  The Balmer series is missing in cool red giants.  Even the sun is missing the Lyman series.  Other elements (and compounds) have various emissions.

Infra-red can be hard from inside earth's atmosphere. 

On the thread topic: It would be nice if most astronomy publications included speculation on the maximum size of civilizations that could be in the image (or data).  Another paragraph on ways a civilization 0.1 higher up the Kardashev scale could camouflage.