An
artist's illustration of a light-sail powered by a radio beam (red)
generated on the surface of a planet. The leakage from such beams as
they sweep across the sky would appear as Fast Radio Bursts (FRBs),
similar to the new population of sources that was discovered recently at
cosmological distances. Credit: M. Weiss/CfA. Low Resolution (jpg)
Cambridge, MA - The
search for extraterrestrial intelligence has looked for many different
signs of alien life, from radio broadcasts to laser flashes, without
success. However, newly published research suggests that mysterious
phenomena called fast radio bursts could be evidence of advanced alien
technology. Specifically, these bursts might be leakage from
planet-sized transmitters powering interstellar probes in distant
galaxies.
"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 of the
Harvard-Smithsonian Center for Astrophysics. "An artificial origin is
worth contemplating and checking."
As the name implies, fast radio bursts are millisecond-long flashes
of radio emission. First discovered in 2007, fewer than two dozen have
been detected by gigantic radio telescopes like the Parkes Observatory
in Australia or the Arecibo Observatory in Puerto Rico. They are
inferred to originate from distant galaxies, billions of light-years
away.
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.
Headquartered
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a joint collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.
For more information, contact:
Megan Watzke
Harvard-Smithsonian Center for Astrophysics
+1 617-496-7998
mwatzke@cfa.harvard.edu
Peter Edmonds
Harvard-Smithsonian Center for Astrophysics
+1 617-571-7279
pedmonds@cfa.harvard.edu
