Fast radio bursts (FRB) are perhaps the most mysterious phenomena we observe in the cosmos. Earlier this year, astronomers announced they had pinpointed an FRB for the first time in a dwarf galaxy that sits three billion light-years away. These intense blasts of radio waves last only 1 to 5 milliseconds, and they have perplexed astronomers since the first one was discovered in 2007.
The leading theories suggest that FRBs come from incredibly volatile cosmic events, such as material being ejected from supermassive black holes, the explosions of superluminous supernovae, or rotating magnetars that lash surrounding material with their immense magnetic fields. But researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) have proposed a much more enticing theory. What if FRBs aren't natural phenomena at all, but rather come from a massive artificial structure used to power alien spacecraft?
"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 Harvard professor Avi Loeb in a press release. "An artificial origin is worth contemplating and checking."
The idea is that FRBs come from an immense alien power plant that is used to propel ships using light sails. A powerful beam of light can propel a reflective surface in the vacuum of space, which is the basis for light sail technology. Current human light sail experiments use light from the sun, but scientists are also working to develop a worldwide system of lasers that could propel small nanoprobes to about 20 percent the speed of light. Such technology, called photonic propulsion, could send a probe to Alpha Centauri, the closet star system to us, in roughly 20 years.
It's possible that a more advanced alien species uses photonic propulsion to power much larger spaceships. Loeb and fellow Harvard researcher Manasvi Lingam found that if an object twice the size of the Earth were harnessing solar power and converting the energy into a laser beam to propel spacecraft, then the radio emissions from it would be detectable even across billions of light-years. Such a planet-sized power system would be capable of accelerating a spaceship weighing a million tons, which is about 20 times bigger than the biggest cruise ships.
"That's big enough to carry living passengers across interstellar or even intergalactic distances," says Lingam.
The team's findings are outlined in a paper titled, "Fast Radio Bursts from Extragalactic Light Sails," which has been accepted for publication in the Astrophysical Journal Letters. To accelerate a spaceship's light sail, the device would need to constantly aim its beams of light at the craft. On Earth, we would see this from time to time as a quick flash of high intensity radio waves rather than a sustained signal because the movement of distant galaxies and planets means the laser would only line up with our planet for a split second.
The fast radio burst that we located earlier this year actually was detected nine times over the course of six months, which, if the signal is coming from an alien power plant, could be an indication that the device lines up with us regularly, or we could be seeing the planet-sized laser system being switched on and off.
Of course, this is all highly speculative theory. The new study simply outlines the fact that it is possible that FRBs are from an alien propulsion system according to our current laws of physics. Our species is nowhere near achieving such advanced technology, but perhaps a more advanced race has unlocked large-scale interstellar travel.
Loeb was asked whether he really believes FRBs come from an advanced alien civilization, to which he responded: "Science isn't a matter of belief, it's a matter of evidence. Deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."
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