Could distant aliens send signals that tell us they exist? If so, how do we know where to look? Researchers focusing on the search for extraterrestrial intelligence, or SETI, have come up with a new strategy to focus their search.
The strategy applies simple trigonometry to millions of data points, with the aim of finding possible interstellar beacons synchronized with astronomical phenomena that are difficult to miss, such as supernovae.
University of Washington astronomer James Davenport and his colleagues presented the design in a research paper submitted to the arXiv print server this month. The idea is also the subject of a speech Davenport gives this week at the Breakthrough Discuss conference in California.
“I think the technique is very simple. “It has to do with triangles and ellipses, things that look like the geometry of high school, which is kind of my speed,” Davenport told GeekWire half-jokingly. “I like simple shapes and things that I can easily calculate.”
The pre-printed document, which has not yet been published in a peer-reviewed journal, is based on data from the European Space Agency’s Gaia sky mapping mission. But Davenport said the technique is tailored to terabytes of astronomical data coming from the Vera C. Rubin Observatory every night when it hits the internet, a few years from now.
Davenport and his SETI colleagues start with a few assumptions: First, aliens must be willing to communicate and must be able to create a medium of communication. “The idea from an alien point of view would be, maybe you have the technology and the ability to make some kind of lighthouse, some kind of lighthouse you want to shine,” Davenport said. “But it’s very expensive to shine in all directions at any time.”
So when do you turn on this lighthouse? One strategy would be to synchronize the flashlight of the lighthouse with observations of cosmic outbursts. “It’s like playing Marco Polo,” Davenport explained. “It simply came to our notice then. Someone shouts “Marco” and you shout “Polo” or you say, “We saw it too. Do you see us? ‘”
The best example of a cosmic explosion in recent times would be SN 1987A, a supernova explosion that occurred 168,000 light-years away and was located on Earth 35 years ago.
The light from the SN 1987A glow has been propagating in an expanding sphere for more than 168,000 years and will continue to spread to farther corners of our celestial neighborhood. If a more distant alien civilization wanted to synchronize the light of its lighthouse with the glow of a supernova, we would see it with a time delay, due to the finite speed of light.
If you know the distance from a given star, it is relatively simple to know when it is on the edge of an “elliptical SETI”, where the time is right for the extraterrestrial lighthouse to appear and for its light to be detected by terrestrial astronomers. But it is not so simple to watch the millions of stars in the ever-expanding ellipsoid.
Two trends in astronomy gradually facilitate the monitoring of the SN 1987A elliptical SETI. One is the move to large-scale celestial probes such as Gaia, which measures the distance to distant stars with unprecedented levels of accuracy. The other is the rise of Big Data analytics tools, such as algorithms being developed at the DiRAC Institute at the University of Washington.
Using such tools, Davenport and his colleagues controlled thousands of stars on Gaia’s list, all 326 light-years (100 parsecs) from Earth. “The vast majority of nearby stars are still viable targets for tracking over time,” they said.
On average, 734 stars will pass through the Elliptical SETI on an annual basis. “While this is a large number of goals that need to be monitored each year, it is well within reach for a lot of research,” say the researchers.
When it comes to scanning the sky for synchronized signals, SN 1987A is not the only game in town: Other elliptical SETIs can be designed for a wide range of astronomical phenomena, including galactic clouds, gamma-ray bursts, and star mergers.
Recognizing what appears to be a synchronized signal would only be the first step in researching a given target.
“The concern is that we end up with a scenario like ‘Wow Signal’ where you have this really interesting signal and there is no repetition or other sequel to show you what it is or if it has ever been repeated.” said Davenport. “This is definitely a concern.”
A seemingly synchronized flash could very well prove to be a cosmic coincidence, possibly involving mysterious anomalies such as blurring and glow in a stellar system known as KIC 8462852 or “Tabby’s Star”. Several years ago, some astronomers suggested that the phenomenon could be detected in an extraterrestrial superstructure, but now the main assumption is that a cloud of dust was the cause. “It’s still a very interesting object, because we still don’t know what dust is,” Davenport said.
Davenport is recruiting students to develop ways to use Big Data more efficiently for SETI. “There are a lot of tricks we can do, and we can write them as algorithms and stick them in databases and computers and large machines and then let them run,” he said.
In addition to the SETI Ellipsoids, such algorithms could focus on what is known as the Earth Transit Zone, a zone of the night sky where extraterrestrial astronomers could theoretically see the Earth passing through our star. In addition to analyzing the Gaia database, Davenport and his SETI colleagues could consider observations from NASA’s Zwicky Transient Facility and NASA’s Transiting Exoplanet Survey Satellite or TESS, as well as data to be created. from the LSST survey of the Rubin Observatory.
Davenport acknowledged that the elliptical search strategy was long-term – so it is important to leverage existing data in the long run, perhaps over the centuries.
“We do not know who other cultures might think is the right way to build a lighthouse,” Davenport said. “We do not know what would make sense to them or what would be obvious. Instead, let’s make the best use of the data we have, because we spend a lot of time, energy and money developing this data for many other reasons. “
In addition to Davenport, the authors of “Searching the SETI Ellipsoid with Gaia” include Barbara Cabrales, Sofia Sheikh, Steve Croft, Andrew PV Siemion, Daniel Giles and Ann Marie Cody.