The Five-hundred-meter Aperture Spherical Telescope (FAST), based in China, is at present the world’s biggest and most sophisticated radio observatory. Even though its primary purpose is to conduct large scale neutral hydrogen surveys (the most common element in the Universe), study pulsars and detect Fast Radio Bursts (FRBs), researchers have planned to utilize the array in the Search for Extraterrestrial Intelligence (SETI). The search for technosignatures, indications of technological activity that indicate the existence of a sophisticated civilization, is integral to this area of study.
Although many potential technosignatures have been suggested since the first surveys began in the 1960s, radio transmissions remain considered the most probable and remain the most studied. An international group of SETI scientists just recently conducted a targeted search of 33 exoplanet systems using a new technique, which they call the “MBCM innured search mode.” Even though the group detected 2 “special signals” in this mode, they dismissed the idea that they were signals from an advanced species. Their survey, nevertheless, demonstrated the effectiveness of this new blind mode and may result in plausible candidate signals later on.
The survey was carried out by experts representing the Fast collaboration, Breakthrough Listen, and multiple colleges as well as institutes. This comprised the Institute for Frontiers in Astrophysics and Astronomy at the 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 Faculty, the College of physics and Electronics at Qilu Normal University as well as the Faculty of Glasgow. The article that describes their work was granted by the Astrophysical Journal for publication.
The very first SETI investigation (Project Ozma) took place under the direction of Professor Frank Drake in 1960, for which the Drake Equation is named. Since that time, nearly all SETI experiments have sought out radio communications as technosignatures, because of their effectiveness in propagating through interstellar space. The very first tests browsed at particular wavelengths, including the absorption line of basic hydrogen (21 cm) as well as hydroxyl (eighteen cm), which corresponds to radio frequencies of 1.4 as well as 1.6 gigahertz (GHz).
Nevertheless, with the development of technology, the accessible bandwidth of SETI devices has grown into the tens of GHz range. In addition, SETI assessments have come to depend on a technique referred to as Multibeam Coincidence Matching (MBCM) to deal with RFI as well as filter it out of their signal noise. Dr. Vishal Gajjar – an investigator in the SETI Institute, UC Berkeley, as well as a co author on the research – revealed to Universe Today through email:
“Single-Dish radio telescopes look at a small portion of the skies, called a beam, about the size of the tip of a pencil kept at arm’s length.” These telescopes frequently detect interference from close by terrestrial sources, in spite of their accuracy. Some telescopes, though, are equipped with multiple beams that enable them to look at a number of parts of the sky simultaneously. By simultaneously looking for signals of interest in all the beams, we are able to figure out in case a signal is actually from a source in the sky, or in case it’s the result of interference. When a signal is detected in several beams, it may be terrestrial interference. “
Based on Gajjar, MCBM is better than conventional techniques for three major reasons. These include:
- Increased robustness and accuracy: MBCM is able to eliminate false positive detections triggered by terrestrial interference, leading to even more accurate results. MBCM is much less prone to interference from terrestrial options, which makes it much more powerful and dependable than standard techniques.
- Faster processing: MBCM may be carried out in real time, rendering it much faster compared to conventional techniques which call for post processing.
- Increased coverage: MBCM provides for a broader field of view by utilizing several beams, supplying much more coverage compared to one beam.
This kind of third advantage was crucial in the task of Dr Gajjar and the international team. The Fast telescope features the most well known radio array on the planet and is equipped with a 19-beam receiver, which enables astronomers to watch 19 unique positions at the same time. The MCMB technique, when paired with the instruments of Fast, effectively removes sources of interference and guarantees accurate observations. For this research, the team observed 33 nearby exoplanets, utilizing the standard MBCM strategy and a new search technique they call the “MBCM innured search mode.”
The blind search mode, as they indicate in their paper, was prompted by the multibeam blind search mode developed recently to study FRBs. The fundamental idea is to use all 19 beams of Fast to look for ETI signals where the central Beam (beam one) tracks a target, even though the others serve as reference beams. Whenever a signal includes non-adjacent beams, more than four adjacent beams, or three or more beams in a line, the group categorized it as RFI. Additionally they recognize 4 beam coverage arrangements which could indicate radio signals of ETI origin.
As demonstrated in the schematic below, any one of nineteen beams of Fast, two adjacent beams (Figure 1a), three adjacent beams forming an equilateral triangle (Figure 1b) and four adjacent beams forming a compact rhombus (Figure 1c) included. Any beam coverage arrangement which did not fit into these 4 groups (like the 3 examples on the second line of the diagram) were considered false positives and dismissed. This particular study builds on earlier work, as Gajjar indicated, where they conducted targeted observations of the same thirty three exoplanetary systems with Fast.
During these inspections, we focused the main beam of our 19-beam receiver at each individual target, and only analyzed data from the central beam where the target was located. Whenever a signal of interest was found, we checked the same frequency throughout other beams to eliminate terrestrial interference. In this work we carry out an even more comprehensive search by blindly looking for signals across all 19 beams, regardless of the existence of any exoplanetary system in the field of view. “This approach allows us to conduct an agnostic search with no prior knowledge of potential targets of interest that are in our beams,” it says.
After looking at these 33 exoplanets, the team discovered 2 somewhat strange as well as fascinating signals. Although it had been difficult to assess these signals (as they showed up in just one beam), Gajjar as well as colleagues determined following a comprehensive examination which they had been only RFI interference:
One of the signals was merely contained in one of the telescope’s 2 polarizations. Usually, sky-based energy sources with an extended period of observation would probably display the same intensity in both polarizations, but this wasn’t the case for the very first signal, making it simple to dismiss it. The 2nd signal was more fascinating, since it displayed the same intensity in both polarizations. “On closer examination, we discovered that the next signal’s frequency was extremely near to recognized sources of interference.”
In another instance, further examination of the data found a signal having an extremely small signal-to-noise (STN) ratio in a single beam. The team dismissed the signal also as its behavior was comparable to other instances of RFI which they’d identified. Although no clear technosignatures have been discovered, the survey was priceless since it tested the silent mode method of the team. Additionally, the 2 signals identified are appropriate targets for follow up observations that may be performed in the coming decades by Breakthrough Listen (the biggest ever SETI effort).
“This is a revolutionary step forward in the area of SETI,” Gajjar stated. “this method continues to be utilized for the very first time in SETI,” it said in a statement. This particular method could be helpful as it lowers the amount of false positives, thus enabling a far more effective search for signals coming from extraterrestrial civilizations. Multibeam coincidence rejection raises the sensitivity of the hunt by decreasing the amount of interference and also makes it much easier to identify weak signals which could otherwise be ignored.
Read more: arXiv