The Breakthrough Listen Project has made several attempts to find evidence of alien civilizations through radio astronomy. His recent efforts focus attention on the center of our galaxy.
The idea behind breakthrough lists is that when alien civilizations are out there they are likely to be sending out radio signals, intentionally or unintentionally. Most of her work has focused on observing stars with potentially habitable planets. The idea was that just like us, they send out radio signals. But by looking at the center of our galaxy, they started looking for more ambitious aliens.
The central region of our galaxy is a great place to point your telescope if you want to listen for signals about thousands of stars. It is the region of the Milky Way where the stars are most densely grouped. The disadvantage is that the center of the Milky Way is outside the galactic residential zone.
The habitable zone of the Milky Way. Photo credit: NASA / Caltech
For a planetary system, the habitable zone is defined by the distance of a planet from its star. Too close and water would boil away, too far and everything would freeze. Obviously, things are not that simple and life could arise in unexpected places, but it is a good rough guide. In principle, it shouldn’t matter where a habitable star system is located in our galaxy, but on cosmic scales it does. Nearby catastrophic events like supernovae and gamma rays could fry life on a young planet. Since the core region of our galaxy is dense with large stars that tend to explode, it is likely to be very hostile to life.
However, if you are a cross-galaxy civilization and want to announce your presence in the universe, you can place a loud radio transmitter near the center of the galaxy where everyone can hear it. So Breakthrough Listen decided to check it out.
The likelihood of a repeating signal from the galactic center. Photo credit: Gajjar et al
For this purpose, the team looked for so-called radio transitions. These are short-term radio bursts that can be caused by things like magnetars and star flares. Since most transients occur randomly in the sky, an alien civilization could be noticed by generating radio bursts with regular periodicity about every few hours. Using the Green Bank Telescope in West Virginia and the Parkes Radio Telescope in Eastern Australia, the team collected 600 hours of radio observations.
As expected, they found no evidence of a repeating alien signal. However, their data were robust enough to rule out repeated signals for up to 10 hours. Perhaps the aliens are playing a longer game, but so far they don’t seem to be talking.
Despite the lack of alien signals, the study found several transient events. These not only help us to understand phenomena like radio-bright magnetars, but they also help us to map the distribution of these objects in the central galactic region. It is a dual duty study that is good for both alien seekers and alien skeptics.
Reference: Vishal Gajjar et al. “The Breakthrough Hearing Search for Intelligent Life Near Galactic Center I.” arXiv preprint arXiv: 2104.14148 (2021).