The search for intelligent life in the universe is getting a major boost from the Breakthrough Listen Initiative, which is the most comprehensive attempt ever to detect alien communications and technologies. Funded by billionaire Yuri Milner, the initiative is currently scanning one million stars within our galaxy, the Milky Way, for signs of alien civilizations.
Now, a pair of scientists have demonstrated that this huge ongoing survey might serendipitously capture signs of aliens in even more remote locations, such as galaxies that appear in the background of images that are focused on stars in the Milky Way.
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These extragalactic objects are not the main targets of Breakthrough Listen, but they could help constrain “the prevalence of very powerful extraterrestrial transmitters,” according to a new study posted on the preprint server arxiv that is co-authored by Michael Garrett, who is the Sir Bernard Lovell chair of Astrophysics at the University of Manchester and the director of the Jodrell Bank Center for Astrophysics, and Andrew Siemion, the director of the Berkeley SETI Research Center and the principal investigator for Breakthrough Listen.
“I think for a while we’ve realized that when we make a SETI observation with a radio telescope, we are sensitive to not only the target star in the center of the field but also a patch of sky about the size of the Moon—so that means we could potentially detect a signal from other objects in the field,” Garrett said in an email to Motherboard.
“Other objects in the field include foreground stars and background stars in our own Milky Way,” he continued. “Until recently, we didn’t know how to make use of this fact because we didn’t know the distance to these stars.”
Fortunately, the European Space Agency launched a space telescope called Gaia in 2013 that has been rapidly filling in this critical information gap by measuring the positions, distances and motions of about one billion astronomical objects.
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The Gaia mission has permitted us to measure distances to a few billion stars in the Milky Way so when we look in these fields we know the distances to quite a few stars that are background and foreground to the target.
Garrett and Siemion co-authored a previous study that explored Gaia’s capacity to aid the search for intelligent life, including technological signals that might originate many millions of light years beyond the stars directly studied by the initiative. These signals are akin to astronomical photobombs, or Easter eggs, that could get overlooked in the data because they are not the primary observational targets.
To figure out the hidden potential of these distant skyscapes, Garrett and Siemion scoured surveys and built a “rudimentary census of extragalactic objects that were serendipitously observed” with the Robert C. Byrd Green Bank Telescope in West Virginia, according to the study. This approach yielded a whopping 143,024 objects, including radiant galactic cores, interacting galaxies, and at least one region where spacetime is warped into what’s known as a gravitational lens.
“It turns out that wherever you point your telescope, the field of view is going to include some interesting cosmic object,” Garrett said. “I’ḿ not sure all SETI researchers had a feel for that, so we decided to look at 400 of the Breakthrough Listen target fields and just see what was in them—that was a lot of fun because the fields are very pretty and you can see some exciting things—like interacting galaxies.”
This wealth of “astronomical exotica,” as the team calls it, could contain traces of alien technosignatures, which are detectable signs of advanced civilizations. These extragalactic transmitters would have to be very powerful to be visible at such enormous distances, but Garrett and Siemion suggest that some speculative technologies might do the trick. For instance, aliens in other galaxies could potentially be spotted if they used phased arrays with thousands of powerful transmitters, or microwave beamers for interstellar sails.
“Our data points are quite useful because although we are only sensitive to really powerful radio signals, the galaxies in a field contain a lot of stars, hundreds of billions, so it might just be possible that because we’re looking at so many stars we might get lucky and find a few of the very powerful signals that might be out there,” Garrett said.
“It was fun to add those data points to the plot and then think about what they might mean,” he continued. “I think they suggest that we want more sensitive telescopes but also with a very wide field of view, so they can observe many stars, etc., simultaneously.”
With that in mind, Garrett and Siemion recommend that scientists involved with SETI consider looking for alien transmissions beyond the objects that are targeted by Breakthrough Listen. After all, the quest to discover if we are alone in the universe amounts to a search for needles in a haystack, so we’ll need to use all the images at our disposal.
“I think this is the first step in thinking about SETI on a very different scale,” Garrett concluded. “Very nearby galaxy groups and clusters are a good place to look for signals because you are pointing in a direction that contains many stars (and therefore hopefully planets, or spacecraft. or whatever else stars attract as good sources of energy for ET intelligence).”
