A survey of billions of stars in the Milky Way could have captured signs of intelligent life, say scientists.
Breakthrough Listen cost $100 million and is the most ambitious SETI (search for extraterrestrial intelligence) project to date.
Now it has released the biggest ever collection of radio emissions from the Milky Way’s ‘plane’, and the region around its supermassive black hole.
This is the flat part that contains the majority of up to 400 billion stars that inhabit the galaxy – and from where an artificial signal is most likely to come.
As daunting as it may seem, the international team is inviting the public to help sift through the information – to identify any advanced civilisations that may be out there.
This means scanning billions of radio channels that might indicate the presence of technology developed outside our solar system.
They need all the help they can get. After four years there is almost 2 petabytes of data. A petabyte is a ‘1’ followed by 15 zeros – or a quadrillion.
Lead system administrator Matt Lebofsky, of the University of California, Berkeley, said: “Since Breakthrough Listen’s initial data release last year, we have doubled what is available to the public.
“It is our hope 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.”
In June a single petabyte of SETI data was released, the largest in the history of the field.
It has been pouring into the Green Bank and Parkes radio telescopes in West Virginia and New South Wales, respectively, which are perfect locations to scan the night sky.
An analysis of radio emissions from 20 nearby stars has already shown an advanced civilisation around them could see Earth pass in front of the Sun – a ‘transit’ used by our astronomers to discover planets beyond the solar system.
Sofia Sheikh, now a graduate student at Pennsylvania State University, has submitted a paper to the Astrophysical Journal after looking for bright emissions at a single radio wavelength.
She said: “This is a unique geometry. It is how we discovered other exoplanets, so it kind of makes sense to extrapolate and say that might be how other intelligent species find planets, as well.
“This region has been talked about before, but there has never been a targeted search of that region of the sky.”
Although her team found no evidence of ET, it is helping to narrow down the places to look.
Astrophysicist Dr Andrew Siemion, director of the Berkeley SETI Research Centre, said: “We didn’t find any aliens, but we are setting very rigorous limits on the presence of a technologically capable species.
“These results put another rung on the ladder for the next person who comes along and wants to improve on the experiment.”
Ms Sheikh’s mentor Professor Jason Wright estimated if the world’s oceans represented every place and wavelength we could search for intelligent signals, we have, to date, explored just a hot tub’s worth.
She said: “My search was sensitive enough to see a transmitter basically the same as the strongest transmitters we have on Earth, because I looked at nearby targets on purpose.
“So, we know there isn’t anything as strong as our Arecibo telescope beaming something at us. Even though this is a very small project, we are starting to get at new frequencies and new areas of the sky.”
If artificial transmitters are not common, then searching for a strong one among the billions of stars in the disk of our galaxy is the best strategy, Dr Siemion said.
On the other hand putting a powerful, intergalactic transmitter in the core, perhaps powered by the 4 million-solar-mass black hole there, might not be beyond the capabilities of a very advanced civilisation.
These may be likely places for aliens to meet up or place beacons, given they cannot communicate among themselves to agree on a location.
Explained Dr Siemion: “The galactic centre is the subject of a very specific and concerted campaign with all of our facilities because we are in unanimous agreement that region is the most interesting part of the Milky Way.
“If an advanced civilisation anywhere in the galaxy wanted to put a beacon somewhere, it would be a good place to do it.
“It is extraordinarily energetic, so one could imagine if an advanced civilisation wanted to harness a lot of energy, they might somehow use the supermassive black hole that is at the centre of the Milky Way.”
Breakthrough Listen looks for electromagnetic radiation consistent with a signal we know technology could produce, rather the background noise from natural astrophysical events.
This also requires eliminating signals from cellphones, satellites, GPS, internet, Wi-Fi and myriad other human sources.
Ms Sheikh turned the Green Bank Telescope on each star for five minutes, pointed away for another five minutes and repeated that twice more.
She then threw out any signal that didn’t disappear when the telescope pointed away from the star.
Ultimately, she whittled an initial 1 million radio spikes down to a couple of hundred, which she was able to eliminate as Earth-based human interference.
The last four unexplained signals turned out to be from passing satellites.
The team intends to analyse all the data released to date and to do it systematically and often.
Dr Siemion said: “Of all the observations we have done, probably 20 or 30 percent have been included in a data analysis paper. Our goal is not just to analyse it 100 percent, but 1,000 or 2,000 percent. We want to analyse it iteratively.”
The venture, expected to run for another six years, was supported by the legendary Sir Stephen Hawking.
Speaking at the project’s launch in 2015, the late British cosmologist said: “Somewhere in the cosmos, perhaps, intelligent life may be watching these lights of ours, aware of what they mean.
“It’s time to commit to finding the answer – to search for life beyond Earth.
“We are alive. We are intelligent. We must know.”
The latest findings were presented at a meeting of the American Association for the Advancement of Science in Seattle.
Billionaire philanthropist Yuri Milner, the founder of Breakthrough Listen, added: “For the whole of human history, we had a limited amount of data to search for life beyond Earth. So, all we could do was speculate.
“Now, as we are getting a lot of data, we can do real science and, with making this data available to general public, so can anyone who wants to know the answer to this deep question.”