*This text was written by a columnist from TechWorld; learn more at the end.
In April and May 2019, the Parkes Observatory radio telescope in Australia picked up a very peculiar signal. This detection, whose origin appeared to be the star system of Proxima Centauri, our closest star neighbor, “only” 4.2 light-years away, was a signal of frequency equivalent to 980 MHz that appeared only once and never was. detected again.
In the search for intelligent life outside Earth, this specific frequency is critical because it is in the range of radio waves that can be generated due to the presence of technological instruments. In other words, this would be a possible detection of so-called technosignatures: markers that provide scientific evidence of past or present technology.
Parkes Radio Telescope, AustraliaFonte: Stephen West
The Parkes radio telescope is part of the ambitious $100 million project called Breakthrough Listen Project, the largest scientific research program ever created to find evidence of intelligent civilizations beyond the Earth that, in addition to including the observation of a million of the stars closest to the Solar System throughout the entire region towards the center of the Milky Way and its disk, will seek to “listen” to another 100 galaxies close to ours.
The captured signal became known as BLC1 (Breakthrough Listen Candidate 1) and offered no immediately obvious explanation. Recorded for about 30 hours, subsequent observations failed to detect it again, an essential fact to confirm a signal such as a technosignature. For these characteristics, many scientists remembered the famous Wow! signal, detected in 1977, which also had characteristics of a possible technosignature. The sign Wow! it was also detected only once, was never fully confirmed and remains unexplained to this day — We will tell this story in another text.
When the BLC1 detection was done, the researchers scanned the Proxima Centauri system in a frequency range from 700 MHz to 4 GHz, with a resolution of 3.81 Hz. And what does that mean? Well, it would be the equivalent of trying to tune in over 800 million radio channels at the same time and with great precision.
Proxima Centauri, the closest star in the Solar SystemSource: ESA/NASA/Hubble
First, astronomers checked whether the signal was constantly changing in frequency over time. Upon detecting a technosignature, the source of the signal, which would be located on a planet outside the Solar System, is expected to move relative to any telescope on Earth that detects it, which would lead to a change in its frequency. This change in frequency is characterized by the famous Doppler effect.
By discarding detections that did not show this variation in frequency, the number of possible cases dropped from around 4.1 million to approximately 1 million. From this, the researchers determined whether this small number of cases seemed, in fact, to come from the direction of Proxima Centauri. To do this, the telescope pointed towards the star and then pointed away, repeating this pattern over and over again. Thus, technosignatures should only appear in observations made when the telescope is looking towards the star. At the end of this process, only the BLC1 signal persisted and became the program’s best candidate so far.
However, what could have ended in a major revelation for humanity and certainly one of the strongest candidates for the Nobel Prize in Physics in the following years, turned out to be yet another misdetection. When Sofia Sheikh, radio astronomer who co-authored these papers, searched a broader data catalog that included observations made on other occasions, she found at least 60 other signals that shared many of the features of the BLC1, but were also detected in observations when the telescope it pointed away from Proxima Centauri. This strongly suggests that the BLC1 is not, in fact, a genuine technosignature but rather some interference from human technology.
But make no mistake! Astronomers are well aware of the forms of interference from radio signals from human instruments, both from those located on the surface and from satellites in orbit. This was not an unfortunate mistake. The BLC1, although it was generated by human interference (though exactly which one is not known), was particularly similar to the type of signal you would expect to come from space. This caused the algorithms and filters for detecting terrestrial radio frequency interference to be misled, which took much longer than usual to conclude that it was a signal of human origin.
Artistic conception of Proxima Centauri b, an exoplanet of 1.3 Earth masses that would be in the habitable zone of Proxima CentauriFonte: ESO
Anyway, the program Breakthrough Listen will continue to monitor Proxima Centauri and other stars, and will continue to refine its algorithms to improve its ability to discriminate between real and false signals. In addition, in the near future, new installations of sophisticated radio telescopes — such as the MeerKAT in South Africa — will make possible significant improvements in sensitivity and observation power, potentially reaching millions of stars per year. Hopefully, this will give us the necessary evidence that we are not alone in the Universe.
Nicolas Oliveira, columnist of tecmundo, has a degree in Physics and a Master in Astrophysics. He is a professor and is currently doing a doctorate at the National Observatory, working with galaxy clusters. He has experience teaching Physics and Astronomy and researching in Extragalactic Astrophysics and Cosmology. It acts as a scientific communicator and disseminator, seeking the popularization and democratization of science. Nicolas is present on social networks as @nicoliveira_.