The study argues that plasma turbulence and stellar activity close to distant star systems may distort radio transmissions before they even leave their point of origin, making them far harder to detect with conventional search techniques.
For many years, scientists involved in the search for extraterrestrial intelligence (SETI) have focused on identifying extremely narrow radio signals – sharp spikes in frequency that are unlikely to be produced by natural cosmic processes. These “narrowband” signals are considered one of the most promising potential technosignatures of advanced civilisations.
However, the new research highlights a potential blind spot in that approach. Even if an alien civilisation transmitted a perfectly narrow signal, it may not remain so by the time it escapes its own stellar environment.
According to the researchers, fluctuations in plasma density within stellar winds – as well as eruptive events such as coronal mass ejection – can distort radio waves close to their source. This turbulence can spread the signal’s energy across a broader range of frequencies, effectively weakening the peak signal strength that detection systems typically rely on.
Lead author Vishal Gajjar, an astronomer at the SETI Institute, said this effect could allow genuine signals to slip past existing search systems.
“SETI searches are often optimised for extremely narrow signals,” Gajjar said. “If a signal becomes broadened by its own star’s environment, it could fall below our detection thresholds – even if it’s actually there. That may help explain some of the radio silence we’ve encountered in technosignature searches.”
To better understand the phenomenon, the team based their modelling on something scientists can observe directly: radio transmissions from spacecraft operating within our own solar system. By analysing how turbulent plasma affects signals sent by space probes, the researchers were able to measure how narrowband transmissions become distorted.
They then extrapolated those measurements to model what might happen in a variety of stellar environments across the galaxy.
The study ultimately produced a framework that estimates how much signal broadening could occur around different types of stars and at various observing frequencies, particularly in highly active stellar environments.
One key finding involves M dwarf stars, small, active stars that make up roughly three quarters of all stars in the Milky Way. Because these stars often produce intense stellar activity, they may be especially likely to distort narrowband transmissions before those signals escape their home systems.
The researchers said this finding could have major implications for how SETI searches are designed in the future.
Co-author Grayce C Brown said adapting search strategies to account for these distortions could significantly improve the chances of detecting extraterrestrial technology.
“By quantifying how stellar activity can reshape narrowband signals, we can design searches that are better matched to what actually arrives at Earth – not just what might originally be transmitted,” Brown said.
The project was supported by the SETI Institute’s STRIDE Program, an initiative aimed at advancing high-risk, high-impact research into emerging questions in the search for extraterrestrial life. The program is funded through the Franklin Antonio Bequest, which supports breakthrough science and education initiatives at the institute.