On August 24, 2001, an intense but fleeting burst of audio signals came to Earth from somewhere millions of light years from us. It was so brief, 5 milliseconds, that it went unnoticed for six years until a team of astronomers, who worked at the Parkes radio telescope in New South Wales, Australia, ran into it reviewing old archive data. The signal was there, the data proved it, but no one knew where it came from or how it had come.

The phenomenon was christened the Lorimer pulse, by Duncan Lorimer, who led the team that discovered that phenomenon hidden in old data. It was not the last, in the last decade since that time, about 25 similar phenomena have been detected, called ‘fast radio bursts’ (FRB), and what was then a curiosity has become a large field of research and the next great mystery that astronomy tries to solve. In fact, at the beginning of this year the origin of one of these bursts was located for the first time, but to study them is not proving anything easy.

When Lorimer found that first sign, he began to meditate. These types of fleeting radio signals usually come from pulsars, neutron stars that rotate at full speed and whose radiation reaches the earth regularly, as if it were the light of a lighthouse. But in this case, the radiation had arrived only once and with much more intensity than any known pulsar until then.

It had to be something else, a totally new discovery. Reviewing data again and again with his colleague Matthew Bailes, an astrophysicist at Swinburne University of Technology in Melbourne, observed a characteristic called dispersion: within these bursts, the lower frequency waves came to us with a slight delay with respect to those of high frequency. This suggested that the signal had traveled far and wide through space for billions of light years and that the source that had generated it had shone for several milliseconds with an energy equivalent to hundreds of times our Sun.

However, the signal did not reappear and the initial enthusiasm became doubtful. Radio astronomers have learned over the decades and disappointments to be cautious, because what seems like a new and unique phenomenon has too often come from mobile antennas, unusual meteorological phenomena or poor calibration of equipment.

Misterious microwaves

In fact, one of the main obstacles in the research of FRB was a well-known microwave. In 2010, Sarah Burke-Spolaor, a doctoral student at that time, began reviewing old data from the Parkes in search of more bursts and located 16 new signals that made everyone doubt the authenticity of the Lorimer pulse.

They were very similar signals, because they showed the same dispersion, but with one crucial difference: these signals seemed to come from everywhere, not just from the point where the radio telescope was pointing. They were called ‘perytons’, in memory of the mythological creature in the shape of a winged deer but cast a human shadow, and the conclusion was clear: they could have been caused by a meteorological phenomenon, or by some human activity, but of course they had Generated on Earth.

When, in 2014, another team, this time at the Max Planck Institute of Radio Astronomy, in Bonn, Germany, published the discovery of a FRB captured at the Arecibo Observatory of Puerto Rico, the existence of this phenomenon was confirmed. But then, what were those ‘perytons’? Emily Petroff, astrophysicist at the Dutch Radio Astronomy Institute decided to solve the mystery.

To begin with, he used the Perkes detector’s improvements to determine when exactly those bursts had occurred, and found that they all took place around mealtimes. This indicated that the origin was not in the meteorology. New ‘perytons’ picked up at that time on a radio frequency suspiciously familiar to the scientists led the team to conduct a series of experiments in the center’s kitchen. It turned out that these signals came from the microwave that the workers were suddenly opening up. The Lorimer event, on the other hand, had been picked up with the radio telescope pointing in a direction totally opposite to the microwave signal from the kitchen. Mystery solved.

Where did they come from?

It took several years and new observations of similar phenomena by other independent teams (in 2015 it was captured in a third center, the Green Bank Telescope in Virginia) to establish the consensus that FRB is a real astronomical phenomenon that Study and unravel. Today they are considered a common phenomenon, and it is estimated that one of these bursts crosses the space approximately every 10 seconds. And yet no one has been able to explain where they come from. Some theories suggest that they are born in black holes in evaporation, colliding neutron stars or huge magnetic eruptions.

And, of course, the alien theory

But last week, scientists at the Harvard-Smithsonian Center for Astrophysics have proposed another possibility, much more exciting but without any proof: what if the FRBs come from a huge artificial structure built by an extraterrestrial civilization to propel their ships? “FRB is exceptionally bright for its short duration and its distant origin, and we have not reliably identified any possible source. It is worth considering and checking for a possible artificial origin,” says Harvard professor Avi Loeb.

Loeb and Manasvi Lingman, the two authors of the investigation (who recognize that theirs is purely speculative), examined how feasible it would be to create a radio transmitter powerful enough to be detectable at such a distance, and concluded that, if The transmitter works with solar energy, it would be enough with twice the terrestrial surface receiving the light of the sun to generate the sufficient power. A construction of this size is still beyond human reach, “but it is possible according to the laws of physics,” say the authors.

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