The survey was performed by scientists representing the FAST collaboration, Breakthrough Listen, and numerous universities and institutes. This included the Institute for Frontiers in Astronomy and Astrophysics at Beijing Normal University, the Beijing Academy of Science and Technology, the Space Sciences Laboratory (SSL) at UC Berkeley, the Institute for Astronomical Science at Dezhou University, the College of Physics and Electronic Engineering at Qilu Normal University, and the University of Glasgow. The paper that explains their work has actually been accepted for publication by the Astrophysical Journal.
The Five-hundred-meter Aperture Spherical Telescope (FAST), located in China, is presently the worlds biggest and most advanced radio observatory. While its primary function is to conduct large-scale neutral hydrogen studies (the most common component in deep space), study pulsars, and identify Fast Radio Bursts (FRBs), researchers have prepared to utilize the selection in the Search for Extraterrestrial Intelligence (SETI). Essential to this field of study is the search for technosignatures, signs of technological activity that suggest the existence of a sophisticated civilization.
While the group detected 2 “unique signals” using this mode, they dismissed the idea that they were transmissions from an advanced species. Their study demonstrated the efficiency of this brand-new blind mode and might lead to possible prospect signals in the future.
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Frank Drake by the Green Bank Telescope. Credit: NRAO/NSF/AUI
The very first SETI experiment (Project Ozma) happened in 1960 under the direction of Professor Frank Drake, for whom the Drake Equation is called. Ever since, most SETI experiments have actually browsed for radio communications as technosignatures due to their efficiency at propagating through interstellar area. The earliest experiments searched at particular frequencies, like the absorption line of neutral hydrogen (21 cm) and hydroxyl (18 cm), which represent radio frequencies of 6.3 and 5.4 ghz (GHz).
But with the advancement of innovation, the readily available bandwidth of SETI systems has expanded into the 10s of GHz range. In addition, SETI surveys have actually pertained to count on a method called Multibeam Coincidence Matching (MBCM) to resolve RFI and filter it out of their signal sound. Dr. Vishal Gajjar, a SETI Institute at UC Berkeley and a co-author on the study, described to Universe Today through e-mail:
” Single-dish radio telescopes observe a little part of the sky, understood as a beam, which is about the size of the idea of a pencil held at arms length. Despite their accuracy, these telescopes typically choose up interference from neighboring terrestrial sources. To overcome this problem, some telescopes are equipped with numerous beams, enabling them to observe numerous little locations of the sky at the same time. By looking for signals of interest in all beams simultaneously, we can figure out if a signal is truly from a source in the sky or if it is a result of interference. When a signal is found in numerous beams, it is most likely to be terrestrial interference.”
According to Gajjar, MCBM is thought about much better than traditional methods for 3 primary reasons. These include:
Increased precision and toughness: MBCM can remove incorrect positive detections brought on by terrestrial disturbance, resulting in more accurate results. MBCM is less susceptible to disturbance from terrestrial sources, making it more reputable and robust than conventional techniques.
Faster processing: MBCM can be carried out in real-time, making it faster than traditional techniques that need post-processing.
Increased coverage: MBCM permits a broader field of view by utilizing several beams, providing more protection than a single beam.
Artist impression of a fast radio burst (FRB). Credit: Danielle Futselaar
The FAST telescope is the worlds largest radio array and is equipped with a 19-beam receiver, permitting astronomers to concurrently observe 19 various positions in the sky. For their research study, the group observed 33 close-by exoplanets utilizing the standard MBCM method and a new search technique they call the “MBCM blind search mode.”
The basic concept is to use all 19 of FASTs beams to search for ETI signals, where the central beam (Beam 1) tracks a target while the others serve as recommendation beams. If a signal covers non-adjacent beams, more than 4 adjacent beams, or three or more beams in a line, the team categorized the signal as RFI.
As illustrated in the diagram below, these included any one of FASTs 19 beams, two of the adjacent beams (Figure 1a), three adjacent beams forming an equilateral triangle (Figure 1b), and four adjacent beams forming a compact rhombus (Figure 1c). Any beam coverage arrangements that did not fit into these 4 classifications (like the 3 examples in the second line of the diagram) were thought about incorrect positives and declined. As Gajjar suggested, this paper develops on previous work where they conducted targeted observations with FAST of the very same 33 exoplanetary systems:
If a signal of interest was found, we cross-checked the very same frequency throughout other beams to remove terrestrial disturbance. In the present paper, we carry out a more extensive search by blindly searching for signals throughout all 19 beams, regardless of the presence of any exoplanetary system in the field of view.
Schematics of the MBCM blind search mode. The very first row shows three examples of permitted signals, and the bottom row shows three examples of forbidden signals. Credit: Luan, Xiao-Hang, et al. (2023 )
After scanning these 33 exoplanets, the group discerned two interesting and rather uncommon signals. As Gajjar associated, while it was challenging to assess these signals (as they just appeared in one beam), after an extensive examination, they identified that they were simply RFI interference:
” One of the signals was only present in one of the 2 polarizations of the telescope. Upon closer assessment, we found that the frequency of the 2nd signal was extremely close to known sources of disturbance.”
By searching for signals of interest in all beams all at once, we can figure out if a signal is truly from a source in the sky or if it is a result of disturbance. The standard concept is to utilize all 19 of FASTs beams to browse for ETI signals, where the main beam (Beam 1) tracks a target while the others serve as referral beams. If a signal covers non-adjacent beams, more than four nearby beams, or three or more beams in a line, the group classified the signal as RFI. As illustrated in the diagram below, these included any one of FASTs 19 beams, 2 of the surrounding beams (Figure 1a), three nearby beams forming an equilateral triangle (Figure 1b), and four adjacent beams forming a compact rhombus (Figure 1c). In the present paper, we perform a more detailed search by blindly browsing for signals across all 19 beams, regardless of the presence of any exoplanetary system in the field of view.
In another case, additional examination of the data revealed a signal in one beam with an extremely low signal-to-noise (STN) ratio. Whats more, the two signals recognized are fitting targets for follow-up observations, which could be performed by Breakthrough Listen (the biggest SETI effort ever installed) in the coming years.
This distinct strategy can be helpful since it lowers the amount of false positives, permitting for a more effective search for signals from extraterrestrial civilizations. By decreasing the amount of interference, multibeam coincidence rejection increases the level of sensitivity of the search and makes it simpler to spot weak signals that might otherwise be neglected.”
Additional Reading: arXiv
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