Fast radio bursts could be coming from 'extragalactic light sails' powering advanced alien spacecraft, scientists at the Harvard-Smithsonian Centre for Astrophysics have said. While the notion seems far-fetched, the researchers say the possibility that these mystery signals from deep space are coming from aliens is "worth contemplating".
FRBs are radio signals that have been detected coming from unknown sources in space. They last just a few millisecond and, so far, only a few dozen have been detected. Furthermore, they are only found in telescope data after the burst has taken place. This means their origin cannot be traced back.
Only one repeating FRB has been discovered so far: FRB 121102. Because it repeated, scientists have been able to trace it to a galaxy three billion light years away. The source of the burst, however, remains a mystery. At present, scientists think it is coming from a massive, highly magnetised and rapidly rotating neutron stars called magnetas.
However, the CfA scientists have said the bursts could be of alien origin. "Fast radio bursts are exceedingly bright given their short duration and origin at great distances, and we haven't identified a possible natural source with any confidence," said theorist Avi Loeb, one of the authors of the study published in Astrophysical Journal Letters. "An artificial origin is worth contemplating and checking."
In the study, Loeb and co-author Manasvi Lingam, from Harvard University, looked at the possibility that FRBs are coming from a radio transmitter strong enough that it could be detected across huge distances. Their findings showed that if it was solar powered, then yes it could.
"We examine the possibility that Fast Radio Bursts (FRBs) originate from the activity of extragalactic civilisations," they wrote. "Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs."
The power needed would be equivalent to sunlight hitting an area of a planet twice the size of Earth. From an engineering perspective, they said that while it is outside our Earthly capabilities, it is not outside the realm of possibly. A water-cooled transmitter twice the size of our planet could withstand the heat, they said.
"The characteristic diameter of the beam emitter is estimated through a combination of energetic and engineering constraints, and both approaches intriguingly yield a similar result which is on the scale of a large rocky planet," they wrote. "Moreover, the optimal frequency for powering the light sail is shown to be similar to the detected FRB frequencies. These 'coincidences' lend some credence to the possibility that FRBs might be artificial in origin."
But why build it? The scientists said the most plausible explanation would be an alien probe. The power from such a device could push a payload of millions of tonnes. "That's big enough to carry living passengers across interstellar or even intergalactic distances," Lingam said.
Loeb added that while the study is very much speculative, it is an interesting point to consider. "Science isn't a matter of belief, it's a matter of evidence," he said. "Deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."