Astronomers on the lookout for evidence of intelligent life beyond Earth can have neglected promising signals just because they’ve targeting a comparatively narrow portion of the radio spectrum.
Most radio SETI (Seek for Extraterrestrial Intelligence) projects have targeted frequencies between 1.42 and 1.66 GHz. This region is commonly called the ‘water hole’ since it falls between the natural radio emissions produced by hydrogen and hydroxyl, which mix to form water.
Researchers have long considered this quiet region of the spectrum a potentially logical meeting place for interstellar communication. A complicated civilization might recognize the importance of hydrogen and hydroxyl and decide to send or monitor signals there.
Searching Beyond the Cosmic Water Hole
Recent research now suggests that higher radio frequencies could offer one other priceless place to go looking for technological signals from distant civilizations. The findings are being presented this week on the Royal Astronomical Society’s National Astronomy Meeting in Birmingham.
Louisa Mason, a PhD researcher on the University of Manchester, used archived observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to conduct the telescope’s first SETI survey.
As an alternative of requesting recent telescope time, Mason examined observations that had originally been collected for unrelated astronomy research. She searched the information for narrowband radio signals, which could possibly be more consistent with artificial technology than with natural processes in space.
“For many years, SETI searches have targeting a comparatively small a part of the radio spectrum. We desired to ask what might occur if we looked somewhere very different,” Mason said.
“The millimeter and submillimeter radio bands remain almost completely unexplored for SETI, so this is absolutely about opening up a brand new area of parameter space to go looking.”
ALMA Opens a Recent SETI Frontier
Mason examined two narrow frequency ranges inside ALMA’s Band 3 observations. The search didn’t discover any candidate technosignatures (alien signals) above the survey’s detection thresholds.
The project was limited to only 4 archived ALMA observations. Even so, Mason says the outcomes show that telescopes operating at higher radio frequencies could turn out to be useful tools in future SETI efforts.
The study also draws attention to an often neglected feature of radio astronomy. When a telescope is aimed toward one object, its field of view normally includes many additional stars in the encompassing area.
These unintentionally observed stars are sometimes described as ‘stellar bycatch.’
Tens of millions of Stars Hidden in Telescope Data
Astronomers have traditionally estimated the quantity of ‘stellar bycatch’ in an commentary by utilizing star catalogues comparable to Gaia. Nevertheless, those catalogues may not include every star in the sphere, particularly objects which might be extremely faint, distant or difficult to discover with confidence.
Mason as a substitute used the Besançon Galactic Model, a simulation designed to estimate the distribution and characteristics of stars throughout the Milky Way. This allowed her to calculate the likely variety of stars captured in each commentary, including many that don’t appear in existing catalogues.
When the tactic was applied to an earlier SETI survey containing 1,327 telescope pointings, the estimated variety of stars included within the search rose dramatically. Gaia data had identified about 288,000 stars, while the galactic model suggested that greater than 6.1 million stars may very well have been observed.
In keeping with Mason, the brand new estimate provides a more complete picture of how much of the Milky Way has already been examined for technosignatures.
“One of the exciting things about this work is realizing that we have surveyed many more stars than initially thought,” she said.
“Even a really small commentary can contain an enormous number and variety of stars that we would never have intended to check. By combining high-frequency observations with galactic simulations, we are able to higher understand exactly what we have searched and where we must always look next.”
No Signal Does Not Mean No Life
Mason cautions that the shortage of a detected signal mustn’t be interpreted as evidence that intelligent life doesn’t exist elsewhere. The search covered only a small variety of observations and two limited frequency windows, and no candidate signal was found inside those specific ranges.
As an alternative, she hopes the work will encourage astronomers to expand SETI surveys across a broader portion of the radio spectrum. It also shows how existing telescope archives could possibly be reused to go looking for possible signs of technology without requiring entirely recent observing campaigns.
The work was done in collaboration with Professor Michael Garrett, Dr. Andrew Siemion and Dr. Kelvin Wandia.
The poster ‘Strategies Utilising High-Frequency Interferometric Data to Explore SETI Parameter Space’ is an element of the Statistical Challenges for Next-Generation Astronomical Surveys session at NAM2026.