It has been almost 60 years now that scientists — a first a few intrepid souls and now many more — have been searching the skies for radio signals that just might be coming from other advanced, technological civilizations. There have been some intriguing anomalies that created great interest, but nothing has to date survived further study.
But two recent developments in the this Search for Extraterrestrial Intelligence (SETI) make clear that the lack of alien signals so far has not diminished interest in the field and in the science and technology behind it. Rather, SETI is alive and doing quite well.
A first sign is scientific and involves what are called “fast radio blasts” or FRBs — high energy pulses that are extremely short lived and, until recently, determined to be sporadic and random. But a paper last week from a Canadian team reported a series fast radio blast from a galaxy a 500 million light-years away that appeared to be repeating about every 16 days.
The authors put forward a number of astrophysical explanations for this most unusual pattern and shied away from any kind of SETI hypothesis. More on this later.
But the detection is the kind of radio signal anomaly that SETI scientists and enthusiasts are looking for. And now they will also have the opportunity to search a vast new trove of data provided by Breakthrough Listen, part of the privately-funded Breakthrough Initiatives.
At the close of a meeting of the American Association for the Advance of Science (AAAS) on Friday, the Breakthrough team announced the release nearly 2 petabytes (2 million gigabytes) of data, the second massive data dump from the four-year old Breakthrough Listen search for extraterrestrial intelligence
The data, most of it fresh from the telescope prior to detailed study by astronomers, comes from a survey of the radio spectrum between 1 and 12 gigahertz (GHz).
About half of the data comes via the Parkes radio telescope in New South Wales, Australia, which, because of its location in the Southern Hemisphere, is perfectly situated and instrumented to scan the entire galactic disk and galactic center. The remainder of the data was recorded by the Green Bank Observatory in West Virginia, the world’s largest steerable radio dish, and an optical telescope called the Automated Planet Finder, built and operated by the University of California, Berkeley and located at Lick Observatory outside San Jose.
All will be available to scientists and the public interested in combing through the data at home in search of anomalies that just might be technological signals.
“Since Breakthrough Listen’s initial data release last year, we have doubled what is available to the public,” said Breakthrough Listen’s lead system administrator, Matt Lebofsky. “It is our hope that these data sets will reveal something new and interesting, be it other intelligent life in the universe or an as-yet-undiscovered natural astronomical phenomenon.”
The data, most of it fresh from the telescope prior to detailed study from astronomers, comes from a survey of the radio spectrum between 1 and 12 gigahertz (GHz).
“This is the largest SETI data release in history,” said Andrew Siemion, an astrophysicist and Breakthrough Listen’s principal investigator
“A core principle of the Breakthrough Listen Initiative is openness in results, instrumentation, observing programs and data. We are excited to be able to share these new data, including some of those from our survey of the galactic plane using Parkes, the galactic center using Green Bank, and those used in our latest science result: a survey of stars in the Earth Transit Zone.”
(The Breakthrough Initiatives is a private venture funded by tech luminaries including Yuri Milner of DST Global, Sergey Brin of Google and Mark Zuckerberg of Facebook.
In releasing the vast store of radio and optical data, Siemion highlighted a new analysis of a small subset of the data: radio emissions from 20 nearby stars that are aligned with the plane of Earth’s orbit. This would allow any advanced civilizations around those stars to see Earth pass in front of the sun. In other words, they could see Earth as it “transits” of our sun in the same way that astronomers here can detect distant exoplanets by measuring the dip in light as they transit in front of their suns.
Conducted by the Green Bank Telescope, the Earth Transit Zone survey observed in the radio frequency range between 4 and 8 gigahertz, the so-called C-band. The data were then analyzed by former UC Berkeley undergraduate Sofia Sheikh, now a graduate student at Pennsylvania State University. She looked for bright emissions coming from the Transit Zone star systems in a single radio wavelength or a narrow band around a single wavelength , and has submitted the paper to the Astrophysical Journal.
If another civilization found our solar system and planets using this transit method, she wrote to me, “then they might be able to look at the spectrum of the Earth’s atmosphere and see that it has chlorophyll or artificial compounds like chlorofluorocarbons. The radio signals we were looking for would have to be the product of that extraterrestrial intelligence figuring out we were here via the above methods (which we know are possible, because we use them!) and then deciding to send an intentional signal to us.”
While Sheikh and her team found no technosignatures of civilization, the analysis and other detailed studies the Breakthrough Listen group has conducted are gradually putting limits on the location and capabilities of advanced civilizations that may exist in our galaxy. The region that was obseved by Green Bank and analyzed by Sheikh, for instance, has never been subject to a targeted SETI search.
“We didn’t find any aliens,” Siemion said, “but we are setting very rigorous limits on the presence of a technologically capable species, with data for the first time in the part of the radio spectrum between 4 and 8 gigahertz. These results put another rung on the ladder for the next person who comes along and wants to improve on the experiment.”
Asked about the newly-identified fast radio bursts that repeat at regular periods, Siemion said that “it’s beginning to look like there might be several different kinds. FRBs do have some properties that are similar to technological emission, e.g. rich time and frequency structure. But so do pulsars, and we know for sure that pulsars are rapidly rotating neutron stars.”
“For the moment the origin of FRBs is a very exciting mystery, and the possibility that some of them are artificial remains just that – a possibility!”
Fast radio bursts – brief but very powerful blasts of radio waves – are one of the most unusual phenomena in deep space. Scientists don’t know what causes them and most are just seen once and don’t repeat. Of those that do repeat, none have been observed to repeat on a regular, cyclic basis. That’s what makes the recent discovery — by Dongzi Li, an astrophysicist at the University of Toronto, and her colleagues — so intriguing.
In their paper, the group at the Canadian CHIME array determined that the radio bursts — named as FRB 180916.J0158+65 — repeated every 16.35 days. The signals arrive about once every hour for a four day period, and then stop. Then about 12 days later they’d start up again. The team observed from September 2018 to October 2019 and detected 28 bursts.
Astronomers have been able to pinpoint the origin of the new FRB as coming from an active star-forming region in a nearby massive spiral galaxy. It’s one of only four FRBs to have its source pinpointed like this, and of those four, it’s the only repeater.
The findings were published on the arXiv.org pre-print site late last month and are awaiting peer review.
The first FRB was detected in 2007 by Duncan Lorimer, an astrophysicist at West Virginia University in Morgantown, and colleagues, and roughly 100 have been identified since. But none have been predictably repeating, like FRB 180916.J0158+65.
“This is very significant,” Lorimer told Science News regarding the new finding. “It’s potentially going to take us in an interesting direction to get to the bottom of these repeaters.”
One possible explanation for the periodicity is that the FRB is orbiting something else, perhaps a star or black hole. In that case, the 16-day period might reveal how often the source of the radio waves is pointed toward Earth. Another possibility is that the repeating cycle is the result of a binary star system.
And yes, it is deemed unlikely, but the burst could possibly be coming from another very distant civilization.
Here is an earlier Many Worlds post on a NASA-sponsored “technosignatures” conference in Houston last year:
Technosignatures and the Search for Extraterrestrial Intelligence