In The Search For Extraterrestrial Signals, No News Isn’t Necessarily Bad News

If extraterrestrial life were to point a telescope toward Earth, what would they see? Would signals from our radios, televisions, and cell phones leaking out into space for their instruments to detect? 

These are among the questions that astronomer Chenoa Tremblay has pondered.

“I’m a lover of science fiction,” said Tremblay, who is a researcher at the SETI Institute, a non-profit research organization with the stated mission of exploring the nature of life in the universe. She wonders what kind of signals a civilization on another world might be unintentionally leaking out into our galaxy. “How would they communicate? Where would they be located?” 

In a pre-print paper shared to the server arXiv.org, Tremblay and two researchers affiliated with the International Centre for Radio Astronomy Research in Australia, detailed their search for signals from extraterrestrial technology – aptly named technosignatures – at the center of the Milky Way galaxy. 

The paper, which was recently accepted for publication to Publications of the Astronomical Society of Australia, is the fourth in a series of papers from Tremblay on surveys for technosignatures and the second of the series to specifically survey our galactic core.

Tremblay had begun using the Murchison Wide Array, a radio telescope in Australia, for other scientific endeavors when she realized it could be used for a SETI-type search for signs of extraterrestrial life. To complete the survey, Tremblay and her colleagues looked at data processed by the Murchison Wide Array.

The study is the first technosignature search at the center of our galaxy focused on the 150 megahertz wavelength, the frequency at which some of our own satellite networks communicate. It’s a less common frequency to search for, but as Tremblay points out, we have no idea at what frequency range another civilization would conduct day-to-day communication like we do with radios, cellphones, and TV.

Though the researchers ultimately didn’t pinpoint any technosignatures, they aren’t discouraged by the results. Existing technosignatures could potentially have been too weak for the telescope to pick up, or not long lasting enough.

“There’s also time involved,” said Tremblay. “If we think of our closest stars being 14 light years away, that means any signal that would have been sent from [a] planet around that star would be some number of years old.” 

As Tremblay points out, on Earth we didn’t start communicating via radio until the first ever radio broadcast on Christmas Eve, 1906. If a civilization more than 116 light years away began pointing their telescopes at us today, they wouldn’t even be able to pick up those signals yet. 

Seth Shostak, a senior astronomer for the SETI Institute, said that the galactic core where Tremblay focused her search is a prime area of interest for extraterrestrial radio signals. He agrees that finding technosignatures at the center of our galaxy could just be a matter of looking for them at the right place and right time.

“They might have all arrived 100 million years ago and the dinosaurs didn’t have a SETI experiment,” said Shostak, who was not involved in the research.

“The galactic center is going to be alive with transmissions,” predicted Shostak. “And the fact that we didn’t find any just means, I think, that the experiment needs to be much more sensitive.” 

Steve Croft, the project scientist for Breakthrough Listen on the Green Bank Telescope, thinks Tremblay’s research represents a “creative way” of showing that searches for technosignatures don’t have to be done on specialized telescopes. Breakthrough Listen, which is a part of the Breakthrough Initiatives founded by venture capitalist Yuri Milner, aims to scan our galaxy and others for radio signals from extraterrestrial civilizations. 

“It’s a really nice indicator of what’s possible,” said Croft, who was not involved with the research. “We’d like to see more of this happening [with] telescopes all over the world.”