An intriguing candidate signal, which was intercepted last year by the Breakthrough Listen project, has been subjected to intensive analysis, suggesting that it is unlikely to originate from the Proxima Centauri system. Instead, it appears to be an artifact of ground-based interference from human technologies, Breakthrough Initiatives announced today. Two research articles, published in Nature astronomy, discuss both the detection of the candidate signal and an advanced data analysis process that can fine-tune “false positives.”
“The significance of this result is that the search for civilizations outside our planet is now a mature, rigorous field of experimental science,” said Yuri Milner, founder of Breakthrough Initiatives.
The Breakthrough List (a program from the Breakthrough Initiatives) is an astronomical science program that searches for techno signatures – signs of technology that may have been developed by extraterrestrial intelligence. The list’s science team, led by Dr. Andrew Siemion at the University of California, Berkeley, uses some of the largest radio telescopes in the world, equipped with the most powerful digital processing systems, to capture data across wide sections of the radio spectrum in the direction of a wide range of celestial targets. The search is challenging because the Earth is flooded with radio signals from human technology – cell phones, radar, satellites, TV transmitters and so on. Searching for a faint signal from a distant star is like picking a needle in a huge digital haystack – and one that changes constantly over time.
The CSIRO Parkes Telescope in New South Wales, Australia (one of the largest telescopes in the Southern Hemisphere, known as “Murriyang” in Wiradjuri) is among the facilities participating in the Breakthrough List search. One of the targets monitored by Parkes is Proxima Centauri, the Sun’s nearest neighbor star, at a distance of just over 4 light-years. The star is a red dwarf orbiting two known exoplanets. The Listen team scanned the target across a frequency range of 700 MHz to 4 GHz with a resolution of 3.81 Hz – in other words, equivalent to tuning to over 800 million radio channels at a time, with exquisite detection sensitivity.
Shane Smith, a bachelor’s researcher working on Listen Project Scientist Dr. Danny Price in the Summer 2020 Breakthrough List internship program, ran the data from these observations through the Breakthrough List search pipeline. He discovered over 4 million “hits” – frequency ranges that had signs of radio emission. This is actually quite typical of the List’s observations; the vast majority of these hits make up the haystack of emissions from human technology.
As with all of the List’s observations, the pipeline filters out signals that appear to be unlikely to come from a transmitter at a great distance from Earth, according to two main criteria:
- First, does the signal change steadily in frequency with time? A transmitter on a distant planet is expected to be moving relative to the telescope, leading to a Doppler operation similar to the change in an ambulance siren as it moves relative to an observer. Rejecting hits without such signs of movement reduces the number of hits from 4 million to about 1 million for this particular dataset.
- Second, for the remaining hits, do they appear to be coming from the direction of the target? To determine this, the telescope points in the direction of the Proxima Centauri and then points away and repeats this “ON-OFF” pattern several times. Local interfering sources are expected to affect both ON and OFF observations, whereas a candidate techno-signature should only appear in ON observations.
Even after both of these data filters have been applied, there are a handful of candidates left who need to be inspected visually. Sometimes a weak signal is actually visible in the OFF observations, but it is not quite strong enough to be intercepted by automated algorithms. Sometimes similar signals appear in neighboring observations, indicating interfering sources that can turn on and off in the wrong period, or the team can track the signals to satellites that commonly transmit in certain frequency bands.
Sometimes an exciting signal remains, which must be subjected to further control. Such a signal of interest was discovered by Smith in the List’s observations of Proxima Centauri using the Parkes telescope. A narrowband, Doppler operating signal that lasted over five hours of observations, which appears to be present only in “ON” observations of the target star and not in the inserted “OFF” observations, had some of the characteristics expected from a techno-signature candidate.
Dr. Sofia Sheikh, who is currently a postdoc researcher on the Listen team at UC Berkeley, dug into a larger data set of observations taken at other times. She found about 60 signals that share many characteristics of the candidate, but which are also seen in their respective OFF observations.
“We can therefore safely say that these other signals are local to the telescope and man-made,” Sheikh says. “The signals are distributed at regular frequency intervals in the data, and these intervals appear to correspond to multiples of frequencies used by oscillators commonly used in various electronic devices. Together, these evidences suggest that the signal is interference from human technology, although we were not able to identify its specific source.The original signal found by Shane Smith is not overtly detected when the telescope is pointed away from Proxima Centauri – but given a haystack of millions of signals, the most likely explanation is still that it’s a transmission from human technology that happens to be ‘weird’ in just the right way to fool our filters. “
The CEO of Breakthrough Initiatives, Dr. S. Pete Worden, said: “Although we were not able to enter into a genuine techno-signature, we are increasingly confident that we have the necessary tools to detect and validate such signatures, if they exist.”
Breakthrough The list makes all data from the Parkes scans available to the public so that they can examine them themselves. The team has also just published two articles (led by Smith and Sheikh) outlining the details of the data collection and analysis, and a research note describing follow-up observations of Proxima Centauri made with the Parkes Telescope in April 2021. Listen will continue to monitor by Proxima Centauri, which remains a compelling target for techno-signature searches using a range of telescopes around the world. And the team continues to refine algorithms to improve their ability to distinguish between “needles” and “hay”, including as part of a recently concluded crowdsourced computing competition in partnership with kaggle.com.
“In the case of this particular candidate,” says Siemion, “our analysis suggests that it is highly unlikely that it really is from a transmitter out on Proxima Centauri. However, this is without a doubt one of the most exciting signals we have seen. to date .”
A mysterious signal looked like a sign of alien technology – but it turned out to be radio interference
Shane Smith et al., A radio technology signature search against Proxima Centauri that results in a signal of interest, Nature astronomy (2021). DOI: 10.1038 / s41550-021-01479-w
Sofia Z. Sheikh et al., Analysis of the Breakthrough Listen signal of interest blc1 with a technosignature verification frame, Nature astronomy (2021). DOI: 10.1038 / s41550-021-01508-8
Provided by Breakthrough Initiatives
Citation: Breakthrough Listen project publishes analysis of previously detected signal (2021, October 26) retrieved October 27, 2021 from https://phys.org/news/2021-10-breakthrough-analysis-previously.html
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