Turns out we were hearing ourselves! Earth can be a noisy place when listening to stars.

Late last year, a story was leaked indicating that the Murriyang radio telescope in Australia had detected a “signal-of-interest”. Dubbed “blc1” (Breakthrough Listen Candidate 1), the signal appeared to originate from the direction of Proxima Centauri, the closest neighbouring star to the Sun. The signal had yet to be fully analyzed when the story was leaked. Now that the analysis is complete, research shows blc1 is in fact “RFI” – radio frequency interference – and not an interstellar signal.

But while it’s not aliens – or “Proxima Centaurians” as lead author on the signal analysis Dr. Sofia Sheikh whimsically refers to them – new methodologies for conducting radio-based SETI (Search for Extraterrestrial Intelligence) have been developed by analyzing blc1; further honing our ability to distinguish future potential ET signals from our own planet.

Simulation of Proxima Centauri b , Rocky World in the Proxima Centauri System – SpaceEngine by author

Needle in a Hay Stack

BLC1 – Breakthrough Listen’s First “Signal of Interest” – with Dr. Sofia Sheikh

From April 29th to May 4th of 2019, the Murriyang telescope targeted ProxCen (Proxima Centauri) to monitor solar flare activity. ProxCen is a red dwarf star located 4.2 light years from Earth. Red dwarfs, are known for their massive solar flares but given that they dominate the stellar population of our galaxy, we want to know how these flares may affect the ability of red dwarfs to harbour life. Mega flares could tear the atmosphere off a planet! ProxCen has demonstrated mega flare activity but also contains at least one rocky planet in the star’s “habitable zone” where it’s warm enough to allow for liquid water.

Murriyang’s scan of ProxCen is intense – 800 million radio frequencies monitored simultaneously spanning the 700Mhz to 4Ghz range. 20TB of information is collected in a matter of days. In addition to flares, Berkeley undergraduate student Shane Smith working with Breakthrough Listen, currently the world’s largest SETI project, used software called turboSETI to scan for signs of alien technology. The software filters signals with certain patterns that may indicate something of interest. After filtering 4 MILLION detection “hits”, one very peculiar signal remained warranting further scrutiny.

Narrowband (technological) signal hits detected in range of the Muriyang telescope. Noted are the registered cellular, satellite, and broadband internet transmitters which can be ruled out immediately as Earth-based signals. c. Smith et al 2021 Figure 2

Smith, found a signal at 982.002571 Mhz, – possibly the SETI winning numbers. Why did this one stand out from the millions of others? Some can be removed straight away as Earth-based signals such as cell-phones and internet transmissions at known frequencies. Another tell is whether the signal still appears when the telescope is pointed “off-source”. At a regular cadence, the scope was pointed away from ProxCen to other calibration sources. If the signal remains when the telescope is moved away from the target, the source of the signal is more likely from Earth and not from the target.

The signals are then checked for “drift.” Drift is the change in a signal’s frequency over time. The hope is that this change in frequency is caused by the source of the signal moving relative to Earth – for example because it is orbiting around a distant star. Its motion creates a Doppler effect similar to the change in pitch of a passing