The Universe looks like a lonely place.
We know we’re proof of it that intelligent civilizations are possible. Finding signs of other civilizations in the Milky Way galaxy isn’t such an easy matter but we have tools at our disposal. Based-on our own technological capabilities, we can extrapolate what signals alien technology might emit & look for those.
These signs are called Technosignatures and efforts in the look for extraterrestrial intelligence (SETI) revolve around them, particularly in radio wavelengths.
“One of the good advantages of the look for technosignatures at radio wavelengths is that we are sensitive to signals emitted from thousands of light years away and it doesn’t take that much power.” told by astronomer Jean-Luc Margot of the University of California, Los Angeles.
“For instance, our search can detect Arecibo Planetary Radar at distances of over 400 light years. And it can detect a transmitter that’s only 1000 times more powerful than Arecibo. A trivial improvement for a complicated civilization. All the thanks to the center of galaxy. The volume of the galaxy that can-be sampled with a radio search for technosignatures is immense.”.
Margot & his team recently conducted search for technosignatures using Green Bank Telescope, a powerful radio reflector in Virginia.
In April of 2018 & 2019, for a complete observing time of 4 hours – they homed in on 31 Sun-like stars around galactic plane-detecting a total of 26,631,913 candidate technosignatures.
A closer analysis of the data revealed that every single one among those candidate technosignatures was generated right here on Earth.
But the methods that used to process those data are a big breakthrough in identifying possible alien technosignatures, teasing them-out from the background humming & pinging of anthropogenic radio noise – what is radio-frequency interference or RFI. Navigation technology, satellite technology, mobile phones, microwave-ovens, aircraft, communications; they’re constantly bathing our surroundings in radio-frequency radiation.
“RFI could potentially obscure an extraterrestrial signal.” Margot said. “RFI makes our job harder because we detect of many signals per hour of telescope time and that we got to make a determination about every single signal: is it anthropogenic or is it extraterrestrial?
“It would be tons easier if we detected only a couple of signals. Fortunately, our algorithms allow us to automatically classify over 99.8% of the signals.”
The team made several improvements to their processing pipeline, refining the sensitivity & detection rate, also because the filter used to automatically classify RFI signals in the data, and thus rule-them out as alien technosignatures.
As Margot noted, these filters correctly flagged 26,588,893 (99.84%) of the signals as anthropogenic RFI. Handling numbers that are enormous, that also leaves tons of data to process. In this case, it was 43,020 signals.
The majority of those remaining signals fell in the range of known RFI & were classified accordingly. That left 4,539 signals might be the most promising alien technosignature candidates. These had to be carefully visually inspected and every single was also ultimately determined to be anthropogenic in origin.
“If a sign is detected in multiple directions on the sky, we will be extremely confident that it’s anthropogenic.” Margot said. “An extraterrestrial signal from an emitter at interstellar distances would be detected in one direction.”
The result isn’t unexpected. A search earlier this year of a way larger stellar sample, 10 million stars also turned up no signs of alien technology. But that wasn’t really the point or a minimum of not the only point.
Firstly, Margot uses SETI data processing as a tool for training students at the UCLA.
“We conduct the search as a part of SETI course that I even have taught at UCLA annually since 2016. This course appears to be unique in the US & maybe worldwide.” he explained.
“Students collect terabytes of data from known or suspected planetary systems, write a data-processing pipeline collaboratively, look for technosignatures in the data & publish the results. It’s most satisfying to witness the scholars acquire important skills that beat the context of this important search.”
The team’s refined pipeline also revealed some issues with previous attempts to process SETI data. More specifically, attempts to quantify what percentage transmitting civilizations there could be within the Milky Way galaxy. Their results show that these estimates could also be too low by upto an element of 15, partially because the data processing pipelines “fail to detect a number of the signals that they’re designed to detect.” Margot noted.
“We implemented a sign injection & recovery analysis tool that permits us to quantify the efficiency of data-processing pipelines. This efficiency must be taken under consideration when attempting to place bounds on number of transmitting civilizations.”
There are some limitations to the team pipeline. Where 2 signals intersect, the algorithm only picks up the one with the very best signal to noise ratio; faint signals against a high-level of background noise are often missed too. It means that regions of high signal density may result in a reduction of the signal recovery-rate.
Overcoming these limitations might be the main target of future work. But it’s work worth doing. RFI is not just a drag for SETI but for all radio astronomers, such a lot in order that some measurements may no-longer be made from Earth. Hence scientists are eyeing the far side of the Moon for a radio-reflector. The Moon acts as a natural buffer against anthropogenic radio- interference.
And of course, there’s a slight possibility but non-zero – that we’d detect something.
“The search may answer one among the most profound scientific questions of our time. Are we alone?” Margot said.
“All life on Earth is related to a common ancestor and the discovery of other sorts of life will revolutionize our understanding of living systems. On a more philosophical level, it’ll transform our perception of humanity’s place within the cosmos.”
The research has been accepted into The Astronomical Journal and available on arXiv.
