A technique that allows radio astronomers to combine observations made simultaneously by multiple arrays has yet to detect any signs of extraterrestrial broadcast signals, Australian researchers have confirmed.
In a study posted online May 29 and scheduled for publication in the Astronomical Journal, experts at the Curtin University International Centre for Radio Astronomy Research used very long baseline interferometry (VLBI) to examine Gliese 581, a star which is orbited by planets confirmed to exist in the habitable zone.
“On 2007 June 19, Gliese 581 was observed for 8 hours at 1230-1544 with the Australian Long Baseline Array,” lead author Hayden Rampadarath and colleagues wrote. “The dataset was searched for signals appearing on all interferometer baselines above five times the noise limit.”
“A total of 222 potential SETI signals were detected and by using automated data analysis techniques, were ruled out as originating from the Gliese 581 system. From our results we place an upper limit of 7 MW/Hz on the power output of any isotropic emitter located in the Gliese 581 system, within this frequency range. This study shows that VLBI is ideal for targeted SETI, including follow-up observations,” they added.
According to BBC News reports, Gliese 581 is a red dwarf star, located approximately 20 light-years away. It also has six planets, including two “super-Earths” resting in the habitable zone, orbiting it, making it “a particularly interesting candidate for the Search for Extraterrestrial Intelligence, or Seti,” the British news agency added.
BBC interviewed Seth Shostak, principal astronomer at the Seti Institute in the United States, regarding the study. Shostak told them that the results were not too discouraging, due to the astronomical odds of even VLBI techniques pinpointing alien life — at least without thousands or possibly millions of observations.
“It’s like they’re looking at the sky through a 6-foot-long cocktail straw – a tiny bit of the sky, so they’re only sensitive to signals that are coming from right around that star system,” he said, adding that terrestrial technology could also be impairing the search. “Figuring out ‘is this ET or AT&T?’ isn’t always easy, and VLBI gives you a good way of discriminating, because if you find something from that tiny, tiny dot on the sky you can say that’s not one of our satellites.”
“Consider the fact that you could’ve looked at the Earth for four billion years with radio antennas – here was a planet that’s clearly in the habitable zone, has liquid oceans, and has an atmosphere – and yet unless you had looked in the last 70 years and were close enough, you wouldn’t have found any intelligent life,” Shostak added. “The fact that we look at one star system and don’t find a signal doesn’t tell you that there’s no intelligent life.”