Free Astronomy Magazine January-February 2022

JANUARY-FEBRUARY 2022 S ofia Sheikh is a radio astronomer and technosignature researcher working as a post-doctoral scholar with the Breakthrough Listen Project. A very complicated flowchart showing the method developed for verifying a signal-of-interest. For a more thorough explanation of the process, see https://seti.berkeley.edu/blc1/flowchart.html. [Flowchart graphics by Z. Sheikh] slightly over a period of about 5 hours. As mentioned above, this is the expected behavior if the signal comes from the surface of another (moving) planet. In reality, this re- quirement is not stringent, as an ar- tificial signal could also come from an apparently immobilized source in space in the short term, for example from a planet with an orbit perpen- dicular to our line of sight, or from a Lagrangian point of that orbit; in these cases there would be no Doppler effect. The length of the signal, nevertheless, made it possible to exclude satellites, airplanes and passing devices at a relatively short distance from the antenna. BLC1 did not appear to be either the result of a recognizable astrophysi- cal phenomenon or a familiar inter- ference of terrestrial origin. The only (reasonable) alternative to these two possibilities was that the signal had originated from occasional radio interference, capable of very faithfully mimicking what the re- searchers expected to discover. To test this hypothesis, Sofia Sheikh, of the Breakthrough Listen team at UC Berkeley, went to “dig” into a larger set of observational data, recorded with Parkes at different times. The new analysis highlighted the exis- tence of about sixty signals that shared many characteristics with BLC1 but which, unlike the latter, also manifested themselves when the radio telescope was aimed at “OFF target.” Here is how Sofia Sheikh commented on the results of her analysis: “We can confidently say that these other signals are local to the telescope and human-gener- ated. The signals are spaced at reg- ular frequency intervals in the data, and these intervals appear to corre- spond to multiples of frequencies used by oscillators that are com- monly used in various electronic de- vices. Taken together, this evidence suggests that the signal is interfer- ence from human technology, al- though we were unable to identify its specific source. The original signal found by Shane Smith is not obvi- ously detected when the telescope is pointed away from Proxima Cen- tauri − but given a haystack of mil- lions of signals, the most likely explanation is still that it is a trans- mission from human technology that happens to be ‘weird’ in just the right way to fool our filters.” We can therefore conclude that BLC1 was not a signal produced by an alien technology. To tell the truth, almost no one among the in- siders has ever considered it an ex- traterrestrial technosignature. The reasons are more than one. First, Proxima Centauri is a red dwarf (type M5.5V) and, as known for stars of this class, often produces very high-power flares that overwhelm its planets with intense streams of radiation lethal to surface life (that is, life as we know it). Another reason is the extreme im- probability that two civilizations of