The source of FRBs, which are milliseconds-long but incredibly bright pulses of radio waves, have intrigued and mystified astronomers for years – and this isn’t the first time aliens have been suggested.
If Fast radio bursts are aliens powering high speed solar sails then
IF each civilization broadcasts only a single beam, this allows us to place a bound on the number of technologically sophisticated civilizations. Using this value in conjunction with the fact that there are∼10 billion habitable Earth-size planets in our Galaxy leads us to the conclusion that there are less than 10,000 FRB-producing civilizations in a galaxy similar to our own. These civilizations must belong to the Kardashev I class at a minimum.
There may be a large number of interplanetary spacecrafts operating at extragalactic distances that are too faint to be detected. In contrast, such spacecrafts (and beams) within our Galaxy are potentially detectable.
The analysis of fast radio bursts gave rise to many interesting consequences. It was shown that the payload of the light
sail and the beam’s characteristic period should be approximately one million tons and beaming lasts about 7 days respectively. Moreover, under certain simplifying assumptions,they derived an upper bound on the total number of intelligent civilizations in a galaxy (akin to the Milky Way).
Loeb and his co-author Manasvi Lingam (Harvard University) examined the feasibility of creating a radio transmitter strong enough for it to be detectable across such immense distances. They found that, if the transmitter were solar powered, the sunlight falling on an area of a planet twice the size of the Earth would be enough to generate the needed energy. Such a vast construction project is well beyond our technology, but within the realm of possibility according to the laws of physics.
Lingam and Loeb also considered whether such a transmitter would be viable from an engineering perspective, or whether the tremendous energies involved would melt any underlying structure. Again, they found that a water-cooled device twice the size of Earth could withstand the heat.
They then asked, why build such an instrument in the first place? They argue that the most plausible use of such power is driving interstellar light sails. The amount of power involved would be sufficient to push a payload of a million tons, or about 20 times the largest cruise ships on Earth.
"That's big enough to carry living passengers across interstellar or even intergalactic distances," added Lingam.
To power a light sail, the transmitter would need to focus a beam on it continuously. Observers on Earth would see a brief flash because the sail and its host planet, star and galaxy are all moving relative to us. As a result, the beam sweeps across the sky and only points in our direction for a moment. Repeated appearances of the beam, which were observed but cannot be explained by cataclysmic astrophysical events, might provide important clues about its artificial origin.
Loeb admits that this work is speculative. When asked whether he really believes that any fast radio bursts are due to aliens, he replied, "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.”
The paper reporting this work has been accepted for publication in the Astrophysical Journal Letters and is available online.
We examine the possibility that Fast Radio Bursts (FRBs) originate from the activity of extragalactic civilizations. Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs. 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. 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. Other relevant quantities, such as the characteristic mass of the light sail, and the angular velocity of the beam, are also derived. By using the FRB occurrence rate, we infer upper bounds on the rate of FRBs from extragalactic civilizations in a typical galaxy. The possibility of detecting fainter signals is briefly discussed, and the wait time for an exceptionally bright FRB event in the Milky Way is estimated.