The search for signs of intelligent extraterrestrial civilizations may have failed to capture potential transmissions due to the concentration of efforts in a restricted area of the radio spectrum. A new investigation points out that higher frequencies, which have been little investigated so far, offer a new chance to identify technological signals of alien origin.
Presentation of the Research
This study was presented during the National Astronomy Meeting of the Royal Astronomical Society, held in Birmingham, United Kingdom. The research was conducted by Louisa Mason, a doctoral student at the University of Manchester, United Kingdom. She used data from the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope, located in Chile, to conduct the first analysis of the Search for Extraterrestrial Intelligence (SETI) program.
Traditional Focus and New Perspectives
Historically, most SETI research has focused on frequencies between 1.42 and 1.66 gigahertz (GHz). This range is known as the 'water hole' because it lies between the natural frequencies emitted by hydrogen and hydroxyl, components of water. Scientists considered this relatively quiet zone a probable location for interstellar communications, given that advanced civilizations might recognize the importance of these elements.
However, the new study argues that higher frequencies also deserve attention in the hunt for technosignatures—signals generated by technology and not by natural cosmic processes.
ALMA Data Analysis
Instead of conducting new observations, Mason examined pre-existing ALMA data, originally collected for other astronomical purposes. The purpose was to detect narrow-band radio signals, seen as potential indicators of technology, distinguishing them from natural astrophysical phenomena. Mason stated that for decades, SETI has focused on a small portion of the radio spectrum, and questioned what would happen if they looked somewhere very different.
She added that virtually nothing has yet been explored from the millimeter and submillimeter radio bands for SETI, which represents the opening of a new parameter area for the search. Although she analyzed two small frequency windows from ALMA Band 3 observations, no candidate technological signature was found above the limits defined in the study. However, she emphasizes that this survey proves that telescopes capable of observing higher frequencies are crucial for future searches for alien intelligence.
Broader Stellar Estimation
Beyond the search for signals, the study revealed an underexplored opportunity in astronomy. When a radio telescope is pointed at a specific target, it also records numerous other stars in its field of view. Typically, researchers use catalogs such as Gaia, from the European Space Agency (ESA), to estimate this stellar population.
Mason employed a distinct methodology, using the Besançon Galactic Model to calculate the entire stellar population present in each observation, including very distant, dim, or difficult-to-identify stars in existing catalogs. By applying this technique to a previous SETI survey, which contained 1,327 telescope pointing observations, the star count increased from about 288 thousand (identified by Gaia) to over 6.1 million, thanks to the galactic model. According to Mason, this offers a much more precise perspective on the extent of the galaxy already examined in the search for technosignatures. She commented that one of the most exciting aspects of the work is realizing that they searched many more stars than initially imagined.
She concluded that even a small observation can contain a large number and diversity of stars that might never have been considered for study. Combining high-frequency observations with galactic simulations allows for a better understanding of what has already been searched and where to look next.
Implications of Non-Detection
The researcher emphasizes that the absence of any signal does not imply that intelligent life does not exist elsewhere in the Universe. For her, the result only indicates that no technosignature was found in the few frequency bands analyzed in this study. It is expected that the work will stimulate future SETI research to explore a larger slice of the radio spectrum and make greater use of the vast volumes of astronomical data already available. The study was conducted in collaboration with Michael Garrett, Andrew Siemion, and Kelvin Wandia.
