A $100 Million Message From Aliens In The Star System Next-Door? What We Know About The Mysterious ‘BLC1’ Radio Signal

Is it aliens? There have been a lot of stories online about the recent detection of a mysterious radio signal from space that appears to have come from the direction of Proxima Centauri—the closest star to our Sun at “just” 4.24 light-years. 

So, it’s aliens, right? It could be, but it’s probably not. First published in The Guardian in December and followed-up by Scientific American, the story revolves around a strange radio transmission detected by the Breakthrough Listen project using the Parkes radio telescope at Parkes Observatory in Australia. 

Could it possibly be a technosignature from a planet orbiting Proxima Centauri—and therefore proof of intelligence on another world? 

Named Breakthrough Listen Candidate 1 (BLC1) though also called “Wow! Signal 2020” because of its similarity to a mysterious radio signal detection in 1977, here’s everything you need to know about the signal “from” Proxima Centauri. 

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What is ‘BLC1,’ who heard it first, and when? 

BLC1 is a curious radio signal detected on April 29, 2019, though discovered by Shane Smith, a student working for the Breakthrough Listen project in archival data in October 2020.

There are said to be scientific papers imminent, but so far all we know is that BLC1 happened only once.

Note the use of the word candidate in its title.

What is a ‘technosignature?’

“Technosignatures” or “technomarkers” are signs of technology developed by intelligent life elsewhere in the Universe. What form do they take? Nobody has a clue. Can we detect them? Ditto.

The most recent conversation about technosignatures occurred in 2025 when astronomer Tabetha S. Boyajian detected the mysterious dimming of a star called KIC 8462852—henceforth nicknamed “Tabby’s Star”—1,470 light-years distant in the constellation of Cygnus. Was it an alien megastructure around the star periodically blocking its light? Probably not. 

However, BLC1 is not a dimming star, but a radio signal that appears to have a technological source. 

What is strange about ‘BLC1?’

BLC1 was a very narrow band radio signal. It occupied the 982 MHz radio spectrum, which is normally used by satellites and spacecraft. It was also only detected once over 30 hours in April and May, 2019.

However, until scientific papers are published—something that is expected soon—the signal’s profile, strength and modulation remain unknown. 

What do experts think the signal is? 

There are lots of opinions—and most of them suggest something other than you-know-what: 

• Since we use radio, it could well be interferences—the signal could have originated on Earth. After all, it’s got all the hallmarks of being artificial and having a technological source. 
• Extraterrestrial technology exists in space because we put it there—it could be from a satellite or a spacecraft. 
• The source is natural, but unknown—maybe it’s a really odd kind of quasar (a supermassive black hole) or pulsar (a highly magnetized rotating compact star) that emits narrowband radio signals. 
• The radio signal is coming from behind Proxima Centauri—possibly millions of light-years beyond. After all, space is big. So it may not be from a nearby star anyway.

The final explanation is: 

• It’s a message from a technologically advanced civilization living on one of the two planets known to be orbiting our nearest stellar neighbor. 

It’s obviously the least likely reason for BLC1. 

What do experts think about BLC1?

Healthy extreme scepticism is the best summary. “Of the 300 million exoplanets that could be habitable in our galaxy, which is 200,000 light years across, it would be an astonishing coincidence for two civilizations—ours and one on Proxima b or c—to be using the same technology at the same time,” said Franck Marchis, a Senior Planetary Astronomer at the SETI Institute.

Marchis suspects a down-to-earth explanation for the signal’s origin. “It’s probably not alien and we will confirm this soon (but) nothing would please me more than to be proven wrong.” 

Have there been any scientific paper on BLC1? 

Only one from Harvard University astrophysicists Amir Siraj and Abraham Loeb, which is published on non-peer-reviewed printspre-print hub arXiv. It argues that a radio-transmitting civilization occupying the next star system along is just so hugely unlikely at eight orders of magnitude.

In fact, it violates the Copernican principle, which tells us that our technological civilization is a single outcome of a random process. 

There is one caveat. Instead of discussing where life could have emerged independently we could consider the possibility that the seeds for life could have been spread in our random corner of the Universe by intergalactic comets—a process called panspermia.

The recent passing through the Solar System of interstellar comets such as 1I/’Oumuamua and 2I/Borisov could be evidence of that.

However, Siraj and Loeb point out that humans appeared on Earth before Alpha Centauri‚ which Prima Centauri orbits—was our nearest star system. It’s suspected that Scholz’s star—a red dwarf star now 22 light-years from us “grazed” the Solar System about 70,000 years ago, coming within a single light-year.

What and where is Proxima Centauri?

Proxima Centauri is the next star along. It’s a red dwarf star—the smallest, coolest and most common kind of star in our region of the Milky Way galaxy. It’s found in constellation of Centaurus, which is visible from the southern hemisphere.

That constellation’s brightest star (and the third brightest in the entire night sky) is Alpha Centauri, a binary star of two Sun-like stars that together are only 4.37 light years distant.

The much smaller, dimmer Proxima Centauri orbits them every 550,000 years, so together they form a triple star system. 

What do we know about Proxima Centauri’s planets?

It has two planets, which makes it not only the closest star system, but also the closest planetary system to Earth that we know of.

The discovery of Proxima b—a planet 20% larger than Earth that orbits its star every 11.2 days—was announced in 2016. Last year the existence of Proxima c was inferred in a paper. About seven times more massive than Earth, Proxima c could be considered a “super-Earth.” It orbits Proxima Centauri every 5.2 years from much farther out. 

Could Proxima Centauri b and c support life?

While Proxima b’s equilibrium temperature is within the range where water could be liquid on its surface, Proxima c is likely too cold.

However, Proxima Centauri—like most red dwarf stars—has a tendency to “flare.” In 2018 a team of astronomers from Carnegie Science detected a massive stellar flare—an energetic explosion of radiation—from Proxima Centauri. On a single day in March 2017 the star’s flare increased its brightness by 1,000 times over 10 seconds. 

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What is ‘Breakthrough Listen?’

“Breakthrough Listen” is at the forefront of the search for extraterrestrial intelligence (SETI). It’s an initiative privately funded by Israeli-Russian entrepreneur, venture capitalist and physicist Yuri Milner to the tune of $100 million to find signs of intelligent life in the universe. Milner and the late Stephen Hawking launched in in July 2015. Its philosophy is to look in as many places, and in as many ways, as astronomers can. 

It’s based at the University of California at Berkeley. 

What was the ‘WOW!’ signal?

BLC1 is also being called “Wow! signal 2020” by some because of its similarity—at least in terms of excitement among radio astronomers—to the famous “WOW signal” received for 72 seconds on August 15, 1977 by the Big Ear radio telescope in Ohio. It was never confirmed. 

If thought to be from a Sun-like star, its source was recently identified by Alberto Caballero of the Habitable Exoplanet Hunting Project as possibly being a star called 2MASS 19281982-2640123 about 1,800 light-years distant in the constellation of Sagittarius.

Did we finally find evidence of extraterrestrial intelligence? Possibly. Maybe. Though probably not. 

Wishing you clear skies and wide eyes.