BLC1 - Breakthrough Listen's First "Signal of Interest"


Breakthrough Listen recently made an intriguing detection using the Parkes "Murriyang" Telescope in Australia, while observing Proxima Centauri, the Sun’s nearest neighboring star. Data spanning a frequency range of 700 MHz to 4 GHz were run through Listen’s search pipeline, resulting in the detection of a narrow-band signal, persisting over five hours of observation, that had some of the expected characteristics of an extraterrestrial transmission. Informally dubbed "BLC1" (Breakthrough Listen Candidate 1), the Listen science team at Berkeley SETI Research Center has spent several months subjecting the signal to further tests. Ultimately the team determined that the candidate signal appears to be interference from human technology, but the analysis provides an excellent test of Listen’s pipeline.

A press release describing the results in more detail is available, and two papers have now been published in the journal Nature Astronomy:


The first (and accompanying supplementary information), led by Berkeley SETI Research Center Summer 2020 intern Shane Smith (a participant in the NSF and Breakthrough Listen supported undergraduate internship program), details the overall search of Proxima Centauri, which is the most sensitive and thorough technosignature search of the nearest exoplanetary system to date, and the most sensitive technosignature search ever undertaken on any star target.

The second (and accompanying supplementary information), led by BSRC Summer 2016 intern Sofia Sheikh (who is now a postdoctoral researcher at UC Berkeley, before she joins the SETI Institute as an NSF Postdoctoral Fellow in 2022), details the analysis of the BLC1 signal and the methodology employed to ultimately rule it out as a technosignature.

A third paper, also led by Sofia Sheikh, reports the results from 39 hours of reobservations of the Proxima Centauri system, in which no recurrences of BLC1 were seen. This paper has been submitted to Research Notes of the American Astronomical Society.


Our open data archive provides access to the datasets used in the three papers, Smith et al. (2021) - Nature Astronomy, Sheikh et al. (2021a), - Nature Astronomy, and Sheikh et al. (2021b) - RNAAS and those with technical skills can analyze them using tools such as blimpy, a tool for loading filterbank, hdf5, and raw format data files, and turboSETI, a tool for performing Doppler drift searches. A technical overview of Breakthrough Listen data is available, as is an overview of Breakthrough Listen’s methodology.

We also invite those with data science skills to explore the data and solutions from our recently completed Kaggle competition. While the competition uses different datasets to those analyzed by Smith and Sheikh, the machine learning solutions explored by participants are helping to develop the next generation of tools that Listen can use to help identify and characterize signals such as BLC1.

Supplementary Information

You can also download the background art seen here (Credit: Breakthrough Listen / Danielle Futselaar - also available as high resolution tif or lower resolution jpg) - an artist’s impression of the Proxima Centauri system. Additional artwork (Credit: Breakthrough Listen / Zayna Sheikh) illustrates the Parkes Telescope observing Proxima Centauri (also available as a lower resolution png).

A video explaining the detection and analysis of the BLC1 signal is available. Also available is a video of a technical seminar by Sofia Sheikh explaining the results.

You may also be interested in a description of the verification process for BLC1, and a Nature Portfolios post about the discovery by Sofia Sheikh.


Background Art by Danielle Futselaar