Scientist says if aliens do exist she knows exactly why we haven't heard them yet

 Astronomers have spent decades scanning the skies for signs of intelligent life - but they may have been looking in the wrong place all along. A study presented at the Royal Astronomical Society's National Astronomy Meeting in Birmingham suggests that alien civilisations could be transmitting signals at higher radio frequencies that have been almost completely ignored by the search for extraterrestrial intelligence (SETI).

Most previous efforts have focused on a narrow band of the radio spectrum between 1.42 and 1.66 GHz, known as the "water hole". This region sits between the natural emissions of hydrogen and hydroxyl - the building blocks of water - and has long been viewed as a logical place for interstellar communication.

Louisa Mason, a PhD researcher at the University of Manchester, decided to look elsewhere. Using archived data from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, she carried out the telescope's first dedicated SETI survey. Instead of requesting fresh observing time, she examined 38 existing observations originally collected for other scientific purposes.

She searched 12 narrow frequency ranges in ALMA's Band 3 for narrowband radio signals - the kind more likely to come from advanced technology than natural cosmic processes. No candidate alien transmissions were detected above the survey's thresholds.

Yet the key insight lies not in what was found, but in what the analysis revealed about the scale of previous searches.

When radio telescopes point at a single target, their field of view often captures many other stars in the background - so-called "stellar bycatch", reported ScienceDaily. Traditional estimates based on star catalogues such as Gaia had suggested one earlier SETI survey of 1,327 telescope pointings had covered about 288,000 stars.

Ms Mason's team applied the Besançon Galactic Model, a simulation of the Milky Way's stellar population, and calculated that more than 6.1 million stars may actually have been observed.

Ms Mason said: "One of the most exciting things about this work is realising that we've surveyed many more stars than initially thought.

"Even a very small observation can contain a huge number and diversity of stars that we might never have intended to study."

The findings highlight two major gaps in the hunt for alien life. First, vast stretches of the radio spectrum - particularly the millimetre and submillimetre bands - remain virtually unexplored for technosignatures.

Second, existing telescope archives already contain far more stars than researchers had realised, offering a low-cost way to expand the search without new observations.

Ms Mason stressed that the absence of a signal in this limited study should not be taken as evidence that intelligent life does not exist. The survey covered only a subset of observations and select frequency windows.

Instead, the research is a call to action. By combining high-frequency data with better models of the galaxy's stellar content, astronomers can both reassess how much of the Milky Way has already been checked and identify the most promising places to look next.

The work, conducted with Professor Michael Garrett, Dr Andrew Siemion and Dr Kelvin Wandia, is detailed in papers published in the Monthly Notices of the Royal Astronomical Society.

If alien civilisations exist, they may be broadcasting continuously - simply on frequencies humanity rarely monitors.