Fast Radio Bursts (FRBs) are short, intense pulses of radio energy that originate billions of light years away. They have incredibly intense energies, but last for only milliseconds, so it isn’t clear what could possibly cause them. Ideas include a neutron star collapsing into a black hole, the collision of two neutron stars, and even an evaporating black hole. Another idea that makes the rounds is that they are produced by an advanced alien civilization.
One idea is that perhaps FRBs are used as some kind of intergalactic navigation beacons, similar to the way we could use pulsars to navigate our galaxy. A more recent idea is that they could be created by an aliens to send space probes to distant stars, similar to Breakthrough Starshot’s idea to use lasers to send a tiny probe to Proxima Centauri. Going directly from “we don’t know” to “therefore aliens” is the realm of science fiction not science, but team of astronomers recently did a bit more than wild speculation. They asked whether it was conceivably possible for such powerful signals to be created artificially.
In the recent paper, they noted that FRBs have characteristics similar to the types of energy beams that could be used to power large light sails. If FRBs are, in fact, being used to power starships, then they would likely be a long lasting beam of energy directed at the starship. We would see them as a short burst because beam would sweep past us as the transmitter and starship line up just the right way. Calculating the energy requirements for such a beam, the team found that a solar powered array about twice the diameter of Earth could collect enough power to create it, and a water-cooled system orbiting a star could transmit the beam without overheating. In principle, at least, alien FRBs appear to be simply a matter of powerful engineering and not exotic physics.
The team went further and estimated the size of a starship that such a beam could power. Rough calculations put the upper size at about a billion tons, or the mass of about 20 cruise ships. For humans that would mean about 40,000 passengers or so, which is plenty large enough to start a colony on another star system. Given that the alien civilization would be capable of making planet-sized power transmitters, you might figure they would have mastered other things like cryogenic freezing or the ability to clone new members of the species once their destination is reached.
This all sounds like wild science fiction, and it’s almost certainly not true. But the team does point some things worth exploring further. Given the number of FRBs we observe, they probably wouldn’t all be caused by alien civilizations. So there would likely be some key signature differences between natural and alien FRBs. In particular, we now know that some FRBs repeat, which means these particular ones can’t be caused by cataclysmic events such as neutron star mergers. Alien FRBs could repeat, since the orbit of the transmitter could bring it back into alignment with Earth periodically. By studying FRBs that repeat, we might be able to see some kind of pattern that points to an artificial source.
There’s a long history of strange astronomical phenomena that seem alien at first, but turn out to be natural after all. FRBs will likely turn out to be natural as well. But it can be worthwhile to cautiously speculate about alien signals. After all, there are a lot of planets out there, and the existence of alien civilizations isn’t beyond the realm of possibility.
Paper: Manasvi Lingam and Abraham Loeb. Fast Radio Bursts from Extragalactic Light Sails. arXiv:1701.01109 [astro-ph.HE] (2017)