There are plenty of strange phenomena lurking in the universe, and fast radio bursts are among the more mysterious. So named for their less-than-5-millisecond duration, the source of these intense, high-energy light bursts continues to elude scientists. Now researchers from the Harvard-Smithsonian Center for Astrophysics are proposing they could have "an artificial origin," specifically from planet-sized alien transmitters for powering interstellar spacecraft.

Fast radio bursts (FRB) were first discovered in 2007 at Parkes Observatory in Australia, with several dozen or so detected since. The initial discoveries showed FRB to be seemingly random one-off events coming from distant galaxies, leading some to hypothesize they were the result of cataclysmic cosmic events, like the merging of black holes or a massive supernova.

But in 2015, an astronomer from McGill University found 11 bursts that not only originated from the same location in space, but were repeating. More repeating FRB were discovered in 2016, which were tracked to a dim dwarf galaxy 3 billion light-years away, poking holes in the cosmic cataclysm idea.

With no consensus on the source of these puzzling phenomena, Avi Loeb and Manasvi Lingam from the Harvard-Smithsonian Center have offered another possibility: advanced alien technology in the form of a solar-powered radio transmitter. These beams of light, they say, could be used to power giant light sails in a "photonic propulsion" system, transporting spaceships or probes through interstellar space that approach the speed of light.

"The system is comprised of two distinct components," Lingam told New Atlas. "The first is a means of harnessing the stellar energy, via photovoltaic arrays for instance. The second is the actual radio-wave beam emitter, which powers the light sail. And the energy for generating the beam comes from the star."

The beam emitter, or transmitter, envisioned by the team is powered by stellar energy, but could conceivably be juiced up through other alternatives. The light reaching Earth as an FRB from such a system would simply be energy leakage, which would mean the gadget would have to be enormous – as much as twice the Earth's diameter. The device would cover a large fraction of the surface of the planet, while Lingam said it's possible the emitter could also be an artificial free-floating structure, like a Dyson sphere.

"The reason for this size is that it enables the effective harnessing of stellar energy and the use of water as coolant," said Lingam. "If the transmitter were smaller, it would undergo more severe heating and would thus be harder to cool. Similarly, if it were smaller, there would not be enough area to tap the stellar energy and power the beam." Lingam added that the coolant would be part of the beam-emitting device, similar to how one uses water as a coolant for lasers.

Informed speculation

The researchers say it's all within the realm of possibilities, at least according to the laws of physics, even if it's far beyond our own technological abilities. It's a no-stone-left-unturned type of suggestion, though Loeb argues that "deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."

At the same time, researchers are currently limited by such a small sample size and their ability to detect FRB, according to Roger Romani, professor of physics at Stanford University. "The rarity [of FRB] is not really clear yet – we have only detected a handful, but even the largest surveys sensitive to these events covered only a small fraction of the sky," Romani told New Atlas. "If extrapolated to the full sky, there should be many FRB per day, but the exact rate is unclear. A number of current experiments are seeking to pin this rate down."

As far as Loeb and Lingam's alien-technology idea, he tends to agree that every possibility should be considered, no matter how improbable it might seem. "I do not think that more prosaic astrophysical origins should yet be eliminated," he told us. "Most would concur that exotic, but astrophysical events likely cause FRB. So I would not sign up for the alien interpretation at this juncture. That being said, this sort of informed speculation is good fun, as long one retains appropriate skepticism."

The research has been accepted for publication in the Astrophysical Journal Letters.

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