Using one of the most sensitive radio telescopes in the world, a trio of Australian researchers set out to hunt for extraterrestrials in the heart of the Milky Way. In late 2020, they pointed their ears towards the galactic center, listening for alien technosignatures. Within their field of view were 144 known exoplanets and, potentially, billions of stars.
But after keeping their ears to the sky for more than seven hours, they heard nothing plausibly extraneous. It seems awfully quiet there.
The research was led by the Murchison Widefield Array, a collection of 4,096 spider-like antennae planted in the Western Australian desert. The antennas, arranged in 256 tiles, can pick up low-frequency radio waves from space. Importantly, the network has a wide field of view, which means researchers can listen for technosignatures — signals broadcast by intelligent life — across a wide region of space. “We are looking for long-standing signals or technological leaks from the daily lives of residents,” explains Chenoa Tremblay, researcher at the SETI Institute in California.
The research is described in a new paper, which appeared Monday on the arXiv preprint repository (PDF) and has been accepted for publication in the journal Publications of the Astronomical Society of Australia.
It’s also not the first time the team has used MWA to search for extraterrestrial signals. They have previously examined the dark forest of our cosmos in 2020 using the MWA, analyzing over 10 million stars, surveyed the galactic center in 2013 and searched towards the Orion Nebula in 2018. They also didn’t hear any alien boos in those three surveys.
However, the new research is different in several ways, according to Tremblay, who is also the first author of the new study. The previous search for the Galactic Center, in 2013, only contained 38 known exoplanets while the new search contained 144. “This is our largest population of known exoplanets in our four surveys with the MWA,” says Tremblay. .
Hunting for life around the galactic center is particularly useful because the region contains the highest density of stars in our galaxy. Where there are stars there can be planets and where there are planets…well, you get drift. “[M]Modeling and our extensive catalog of known solar systems suggest that there is a good chance that habitable planets are heading towards the galactic center,” notes Tremblay.
The amount of stars in the new research is difficult to predict accurately because the galactic center is very dusty, obscuring the view of the surveys and preventing an accurate reading. Previous research has used data from the Gaia Space Observatory to count the number of stars, but that doesn’t work at the Galactic Center. Tremblay explains that the team used a different survey, known as Galactic Nucleus, which ranked 3.3 million stars. However, the survey covers less than 1% of the area surveyed by MWA.
“If we extrapolate that, we cover billions of star systems right down to the center of our Galaxy,” notes Tremblay.
That’s, in theory, a lot of chances to hear from extraterrestrial friends. However, that’s still just a drop in the cosmic ocean – there are plenty of other places where alien technosignatures could emanate from.
It was also the first time that a search was performed at a high frequency of 155 MHz. This reduced the chances of picking up daily ground communications and interference. Previous research focused on the lower frequencies between 98 and 133 MHz. Of course, this comes with a big caveat: we kind of assume that these alien technologies are using the same technologies as us to broadcast.
The MWA is currently undergoing an upgrade that will allow searches at different frequencies and time resolutions, giving it the ability to match other technosignature searches like those conducted by the Breakthrough Listen collective. Tremblay notes that the 256 tiles containing the spider-like antennae will be able to image the sky once the upgrades are complete.