Just 4.2 light-years away, there is a faint star called Proxima Centauri. It is a red dwarf, smaller and darker than the Sun, belonging to a three-star system in the constellation Centaurus. Proxima Centauri is inconspicuous in the Brilliant Constellation of the Milky Way, but it is of great significance to humanity, it is the closest star to the Sun, and it is also the home of the trisolaran people of the extraterrestrial civilization in the famous science fiction novel "Three-Body".
The three-star Centauri system, the lower right corner is Proxima Centauri
Everyone knows that "The Three-Body Problem" is a fictional literary work, but in 2020, scientists found a mysterious signal from the direction of Proxima Centauri through a large radio telescope, and after careful checking, it was judged that this signal was completely different from those ordinary radio interferences from Earth, and it was likely that it really came from Proxima Centauri 4.2 light-years away! As soon as the news came out, it immediately caused a huge controversy and discussion, is this the communication sent by the Trisolaran to Earth? Now, this signal has finally been cracked!
The signal, known as BLC1, was detected by the 64-meter-aperture Parks radio telescope in Australia and discovered by Shane Smith, an undergraduate student at Hillsdale College in Michigan, who participated in the Breakthrough Listening program dedicated to searching for extraterrestrial civilizations. Shane analyzed six days of observations from the Parks telescope between April and May 2020, of which 26 hours were obtained by the telescope aimed at Proxima Centauri.
The data from proxima centauri directions includes more than 4 million radio signals, but one of them is very special, it lasts for 5 hours, has a frequency of 982 megahertz, and is called BLC1, which translates to "Breakthrough Listening Candidate 1". The signal fully meets the identification criteria for radio searches by extraterrestrial civilizations, and does not appear to be naturally generated by stars and planets, or interference from electronic or communication devices on Earth.
A mysterious signal from the direction of Proxima Centauri BLC1
In general, stars and planets will be huge sources of radio signals, but they produce a wide range of signal frequencies, while the BLC1 band is very narrow, limited to 982 megahertz, so it can be ruled out that it is emitted by a celestial body, it is more like some kind of communication signal. Its frequency is still slowly drifting for 5 hours, possibly caused by the Doppler effect caused by the movement of the signal source.
The researchers also searched the communication frequency bands of various spacecraft such as satellites, and could not find an object that could match BLC1. In Australia, the frequency band around 982 MHz was reserved for aircraft, but no planes passed through the area at the time, and aircraft communications would not last up to 5 hours!
Even more mysterious is that the BLC1 signal appears only once and has not been observed since. Since BLC1 was only discovered while observing Proxima Centauri and did not appear in any other direction, it seems to indicate that the signal is related to Proxima Centauri, and given proxima centauri's importance, BLC1 has attracted widespread interest from extraterrestrial civilization seekers around the world.
Proxima Centauri is the closest star to the Sun
Why do signals from the direction of Proxima Centauri get so much attention? Because the identity of this star is so special, there is indeed a possibility of extraterrestrial life in its vicinity. Just like echoing the "Three-Body" novel, scientists have found through observation that Proxima Centauri really has a planet that is equivalent to Earth, with a mass of about 1.3 times that of Earth and an orbital period of 11 days, known as Proxima B.
In recent years, astronomers have found many planets outside the solar system through methods such as occultation, which has opened our eyes: it turns out that having planets is not the sun's patent, and planets abound in the universe. But the vast majority of the planets found are gas giants like Jupiter, tens or hundreds of times larger than Earth, and are not suitable for life. A very small number of rocky terrestrial planets, either too close to their parent star, too hot to be hellish, or too far away, are a frozen world.
Proxima B is an exciting, even a little scary planet. It's about the same size as Earth and can retain an atmosphere, which is already quite rare in itself, and more importantly, it is also in the habitable zone of Proxima Centauri, where the temperature is not too high or too low, and the important substance of life, water, can exist in liquid form. The right size + the right temperature, such a planet so friendly than life, is located near the nearest star to us, and it is extremely frightening.
The existence of Proxima b was confirmed in 2016 , inferred from the motion of Proxima Centauri , and it is likely that Proxima Centauri also has a larger Jupiter-like planet , Proxima Centauri c , but farther away from the host star and therefore very cold. In this way, Proxima Centauri has both rocky planets in the habitable zone and gaseous planets such as Jupiter, and perhaps other undiscovered planets, which is simply a copy of the solar system, and the hope of extraterrestrial life is greatly increased.
Comparison of Proxima Centauri's habitable zone with Mercury's orbit
It is for the sake of all these factors that if a radio signal is confirmed to have come from the vicinity of Proxima Centauri and meets certain characteristics of the communication signal, then we have reason to suspect that the signal was sent by some extraterrestrial civilization, and the BLC1 signal falls into this category. Are the Trisolarans really calling humans? This possibility cannot be ruled out, because Proxima Centauri is so close to us that electromagnetic waves only need 4.2 years to reach, and an intelligent species that has reached a very high civilization level should have the ability to send signals to Earth.
Unfortunately, this conjecture, which excites sci-fi fans, has recently been overturned. On October 25, 2021, the journal Nature claimed to have cracked the most likely source of BLC1 signals: intermodulation interference from an electronic device on Earth. Intermodulation is when two or more different frequency signals act on a nonlinear circuit, will be modulated to produce a new frequency signal, if the frequency falls exactly within the receiver operating channel bandwidth, it will constitute interference with the receiver. Guitar amplifiers can also sometimes produce this distortion.
The cause of BLC1 is most likely intermodulation interference
But determining which device generated the signal became a challenge. The researchers said BLC1 may have come from a communications device within a few hundred kilometers of the Parkes telescope, that it may have malfunctioned or is being repaired. The drift characteristics of BLC1 signals are also similar to the crystal oscillators used by ordinary computers and mobile phones. They also developed an artificial intelligence algorithm that tried to find out the frequency of the signal before distortion, but there was no result yet.
But while the BLC1 source nature has been deciphered, there's a question that can't be explained: Why did the Parks Radio Telescope only appear with this particular signal when it was aimed at Proxima Centauri? The researchers believe that this is most likely just a coincidence: they just caught up!
This isn't the first time this has happened: In 1977, scientists also captured a powerful narrowband radio signal, 30 times stronger than the background radiation, lasting 72 seconds, named "Wow!" At one time, many people thought that it was sent by aliens, and now the more reasonable explanation is that there were exactly two comets skimming near the Earth, and the comet was illuminated by the sun to produce a hydrogen cloud, which may emit a radio signal.
WOW！ Signal
If the BLC1 signal is forcibly interpreted as emitted by aliens, there is also a disadvantage, that is, proxima b, although in the habitable zone, is too close to the parent star realization, only 7.5 million kilometers, and the orbital period is only about 11 days. Proxima Centauri, although it is very faint and the fusion reaction is not so strong, it also causes the fusion energy to flow smoothly through the star's outer shell and accumulate inside.
When the energy accumulates to a certain extent, it will suddenly erupt in the form of a super flare and release a large amount of ultraviolet light. As a result, the flares of young red dwarfs are very frequent and intense, and planets that are close to them are often baptized by strong ultraviolet rays, and the atmosphere may be stripped away and the surface will turn into scorched earth. Proxima Centauri is precisely such a red dwarf, and Proxima b, which is particularly close to it, may be bombarded with super flares several times a day, and the probability of life being born and evolve civilization is minimal.
Observe Proxima Centauri on Proxima B, which will be much larger than the Sun seen on Earth
Although after all kinds of research and inferences, the possibility that BLC1 is an alien call is almost impossible, but the analysis process for it is still very valuable. When people find some special signals again in the future, they can learn from these methods to better identify the nature of the signals, which will be of great help to the search for extraterrestrial civilizations like a needle in a haystack. China's 500-meter "China Sky Eye" FAST radio telescope will have a relatively strong capability in this regard.