A groundbreaking new study from the Breakthrough Listen Initiative suggests that radio-bright galaxies — those that emit intense levels of radio waves — could potentially host multiple advanced extraterrestrial civilizations. This revelation reshapes our understanding of how and where intelligent life might exist across the universe, highlighting that our search for technosignatures may need to look beyond individual stars to entire galactic populations.
For over six decades, scientists working on the Search for Extraterrestrial Intelligence (SETI) have been listening for signs of alien radio transmissions. Beginning with Project Ozma in 1960 and evolving into the sophisticated Breakthrough Listen project launched in 2016, researchers have scanned the cosmos for any whisper of artificial radio activity. Breakthrough Listen, backed by billionaire Yuri Milner and supported by observatories like Green Bank, Parkes, and the Automated Planet Finder, represents the most comprehensive SETI effort to date.
The latest findings, published in the Publications of the Astronomical Society of the Pacific, come from Dr. Brian K. Lacki, a theoretical astrophysicist and Jansky Fellow at the U.S. National Radio Astronomy Observatory (NRAO). His study, titled “Artificial Radio Transmissions as Galactic Populations,” explores the intriguing idea that galaxies with unusually strong radio emissions could harbor vast networks of technologically advanced societies — possibly even Type III civilizations on the Kardashev Scale, capable of harnessing the energy of entire galaxies.
According to Lacki, rather than focusing on detecting signals from single planets or stars, SETI could detect collective technosignatures — the combined radio output of numerous civilizations within a galaxy. In his model, if even a small fraction of the civilizations across a galactic population were broadcasting simultaneously, the galaxy itself would appear artificially radio-bright.
Galactic technosignatures present both an exciting and complex challenge. Natural astrophysical sources, such as supermassive black holes at the centers of galaxies — including Sagittarius A* in our own Milky Way — already emit strong radio signals. This makes it extremely difficult to distinguish between natural radio emissions and those potentially generated by intelligent life. Lacki’s research introduces the concept of a “collective limit” — a statistical threshold for how much radio brightness could be attributed to artificial sources rather than natural ones.
Using computational models, Lacki simulated different galactic environments, factoring in the number of civilizations, transmission strength, frequency ranges, and energy consumption levels. His analysis found that truly advanced Type III civilizations — those radiating as much energy as an entire galaxy — are exceedingly rare. The study estimates that fewer than one in 100,000 Milky Way-sized galaxies could host such civilizations. However, Type II.75 civilizations, capable of emitting roughly one-third of their galaxy’s total radio luminosity, might exist in as many as one in 100 major galaxies.
This statistical framework allows SETI scientists to set upper limits on how many galaxies could plausibly host intelligent life based on radio emissions. It also provides a method for targeting future searches, focusing on galaxies that are dimmer in the radio spectrum but rich in stars — ideal candidates for containing smaller-scale civilizations.
Lacki’s approach draws parallels with previous Dyson Sphere searches, which look for infrared excesses caused by megastructures absorbing and re-emitting starlight. Similarly, if alien civilizations are generating massive radio outputs, they could collectively make their galaxies appear brighter in the radio band. However, identifying these anomalies requires careful distinction between artificial and natural emissions — a challenge that remains one of SETI’s greatest technical obstacles.
Beyond radio frequencies, the study encourages expanding SETI’s scope to include X-rays, gamma rays, and optical technosignatures, which could complement traditional radio searches. This broader strategy could help uncover civilizations that rely on different technologies or communication methods than those envisioned in classic SETI frameworks.
Conclusion:
While the new research doesn’t claim direct evidence of alien civilizations, it significantly refines our understanding of where and how to look for them. Instead of treating civilizations as isolated anomalies, scientists may need to view them as potential galactic-scale populations influencing entire systems’ electromagnetic signatures. As Dr. Lacki puts it, even if most radio signals we detect are natural, “we can still establish powerful limits on how common truly advanced civilizations might be.” The future of SETI, it seems, lies not just in listening to the stars — but in studying the cosmic chorus of entire galaxies.
