The star system KIC 8462852 made headlines a few weeks ago for its mysterious dimming by 20 percent and more. That is a huge amount of dimming, and its irregularity also aroused interest, since the tiny, but regular waxing and waning of light from stars is so commonly seen and studied. Astronomers proposed several natural explanations to explain KIC 8462852’s light, but the possibility that aroused everyone’s interest was that a technologically advanced, alien civilization has built megastructures – sometimes called Dyson spheres – in orbit around the star. This week (November 5, 2015), the SETI Institute announced it has now trained its Allen Telescope Array on this star, in the search for deliberate signals. It said it found “no clear evidence” for such signals within a certain range of frequencies.
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The unfolding of the story of KIC 8462852 is very interesting in itself. You can read it here.
What is a megastructure or Dyson sphere? One of the ways astronomers contemplate seeking advanced alien civilizations is to talk about what they might build. We on Earth are only now beginning to speak of solar power for wide-scale energy use by humans, and it’s easy to see that solar arrays set in a large desert would gather more sunlight than an array on your roof. Now imagine if we covered the entire Earth with solar arrays; we could gather much more power, but where would live?
The answer would be to move the solar arrays to space.
Thus astronomers have imagined a civilization that was extremely advanced and able to build a megastructure in space – a so-called Dyson sphere – that would consist of swarm of solar panels for large-scale energy collection.
There is the hypothetical, but intriguing, possibility that an advanced civilization might try to collect all the energy from its star.
Other possible megastructures – signs of an alien civilization – would include artificial space habitats, or a planet-sized or larger occulting object intended to provide a long-lasting signal to other galactic inhabitants.
How did the SETI Institute conduct its search? The 20% drop in energy from star system KIC 8462852 has set some astronomers’ imaginations to work. What if the drop comes from obscuring material near this star, and what if that obscuring material is artificial, not natural. Could it be large solar power arrays? Several groups of astronomers have recently turned telescopes on this star, but a search by the SETI Institute will always be of high interest since, after all, SETI means “search for extraterrestrial intelligence.” They are the experts in this search, in other words.
The group of SETI astronomers used the Allen Telescope Array, which is is located approximately 300 miles (500 km) north of San Francisco, California in the Cascade Mountains. It consists of 42 antennas, each about 20 feet (6 meters) in size.
According to a November 5 statement from the SETI Institute, they sought two different types of radio signals:
1. Narrow-band signals, of order 1 Hz in width, such as would be generated as a “hailing signal” for societies wishing to announce their presence. This is the type of signal most frequently looked for by radio SETI experiments.
2. Broad-band signals that might be due to beamed propulsion within this star system. If astroengineering projects are really underway in the vicinity of KIC 8462852, one might reasonably expect the presence of spacecraft to service this activity. If these craft are propelled by intense microwave beams, some of that energy might manifest itself as broad-band radio leakage.
SETI Institute scientist Gerry Harp commented:
This is the first time we’ve used the Allen Telescope Array to look for relatively wide-band signals, a type of emission that is generally not considered in SETI searches.
What did the search reveal? The SETI Institute’s November 5 statement concluded:
Analysis of the Array data show no clear evidence for either type of signal between the frequencies of 1 and 10 GHz. This rules out omnidirectional transmitters of approximately 100 times today’s total terrestrial energy usage in the case of the narrow-band signals, and ten million times that usage for broad band emissions.
While these limits are relatively high – a fact due primarily to the large distance (>1400 light-years) of KIC 8462852 – one should note the following:
1. The required transmitter power for the narrow-band signals could be reduced enormously if the signal is being deliberately beamed in our direction.
2. Microwave propulsion schemes would undoubtedly be beamed as well, and that would also reduce the minimum transmitter power necessary for detection by the Array.
Finally, note that any society able to build a Dyson swarm would have access to energy at a level approaching 1027 watts. Even omnidirectional transmitters would be detectable if only a tiny percentage of this energy were used for signaling.
SETI Institute astronomer Seth Shostak added:
The history of astronomy tells us that every time we thought we had found a phenomenon due to the activities of extraterrestrials, we were wrong. But although it’s quite likely that this star’s strange behavior is due to nature, not aliens, it’s only prudent to check such things out.
The SETI Institute said observations will continue.
This work can be found at https://arxiv.org/abs/1511.01606
Bottom line: After a two-week search with the Allen Telescope Array in California, no evidence has been found of deliberately produced radio signals from KIC 8462852. This is the star system that made headlines a few weeks ago for its possible alien megastructure, aka a Dyson Sphere.