By Chariton Tomboulidis, Astrophysicist

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8/6/2020

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In my first little booklet that was printed publicly by the local newspaper of Naousa, “To Neo Vima”, in 1986, I wrote:

 

“The greatest trial for our existence in the world is perhaps its loneliness. That’s why the thought that we are not alone among billions of suns is both tempting and comforting. From a scientific point of view we don’t know what to believe, and under these conditions, it’s better to believe that we have company.
Perhaps there are swarms of life on distant planetary systems and maybe, on some of them, the beings are intellectual and indeed searching for contact.

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Efforts to hear something from them have been ongoing since the early 1960s with large radio telescopes. We have even sent playful messages to nearby stars. The fact that we haven’t yet received a reply is not strange. There are far too many stars in our Galaxy to search. What is needed from the astronomers involved in the Search for Extraterrestrial Intelligence (SETI) is patience and optimism. Some are disappointed and a bit anxious because we have so far received no answer, since they believe that extraterrestrial civilizations should be millions or billions of years old and thus advanced enough to detect our radio waves. Are we alone, or are they simply ignoring us? Perhaps they’re sitting in their nest and don’t care, having already seen our TV programmes. Someone floated the idea of a Galactic Club, whose members are only those civilizations that are spiritually and psychologically mature, who communicate using higher methods of communication, far superior to ours, of the beginners. The proposal seems typical of our cultural dreams: Man ceases to feel alone and has something higher to strive for a membership card of the club.

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All this sounds more or less like science fiction stories, but perhaps one day we’ll be sitting in front of a long printout (from some computer) containing information from an extraterrestrial civilization. This information, which could be collected in a few days with a radio telescope once contact is achieved might represent the total research output of many millions of years. It might be difficult to comprehend, the military would be very worried and scratching their heads in confusion, and it might bring a radical change in our way of life and our civilization.

If you don’t believe in such things, you should be ready to accept the possibility that we are completely alone in the Universe.”

More than thirty years have passed since then. We have sent probes to search for extraterrestrial forms of life to search for other planets. And thus we introduced the term “extrasolar planets”: planets that orbit around other suns, around other stars. These discoveries are made optically, using photometry and spectroscopy, and they are not at all difficult if you have a bit of luck and the right observing instruments. It is what one scientist once said: “It’s like looking for a needle in a haystack.” Yet, with the technology we have today, it is not so hard to find that needle. And that is what some researchers are doing today. So far, more than 3,660 extrasolar planets have been discovered, all indirectly of course, because it is impossible to photograph planets that do not shine, orbiting bright stars.

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There is, however, also a telescope that looks specifically for Earths and orbits in space around our own planet. It is called Kepler, and it started operating in 2009, observing thousands of stars.

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Up to now it has found a little over 1,000 extrasolar planets, and recently several “new Earths”, that is, planets which may have water in liquid form. This was big news for the media and the general public, whereas for me it was hardly news at all. Because Earth like worlds exist everywhere indeed with liquid surfaces and water in liquid form. But did Kepler perhaps also find an extraterrestrial technologically advanced form of life? Did it maybe find one of the spheres that the scientist Dyson predicted in the 1960s and which now bear his name? Did they find a Dyson Sphere?

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Physicist Freeman Dyson proposed the idea that advanced civilizations which need ever more energy in order to expand beyond their planetary system might harness the immense energy emitted by their star, constructing gigantic solar collectors around it, so as to absorb a large part or even all of that energy.

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In the autumn of 2014, some amateur astronomers who were hunting for extrasolar planets in the data of the space telescope Kepler noticed some strange irregularities in the brightness of a star listed in astronomical catalogues as KIC 8462852. The variations in the star’s brightness showed a unique, irregular and thus unusual pattern, which had not been observed in any other star in the Galaxy and could not be explained by a transit (a planet passing in front of the star) of a companion planet. Many ideas were put on the table as to what might be causing this behaviour including the suggestion that it might be the work of an extraterrestrial technologically advanced civilization.

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The head of the citizen science programme “Planet Hunters”, Tabetha Boyajian, after carefully checking and confirming the data and ruling out any possibility of errors in recording or processing, proceeded in 2016 to a collective scientific publication. That star is now known as Boyajian’s Star, or “Tabby’s Star”, in recognition of the significance and peculiarity of the case, since astronomers have not found an explanation that accounts for all aspects of the phenomenon. Could KIC 8462852 be the first proof that advanced extraterrestrial civilizations do not belong only to the realm of science fiction? Before Kepler was launched into orbit, planet hunters were discovering extrasolar planets one by one. Kepler sweeps sectors of the sky and reveals their existence around many stars, thousands at a time.

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For four years the telescope observed stars in a small region of the Galaxy, detecting extrasolar planets by the small, periodically recurring dips in stellar brightness when a planet happens to pass between its star and our line of sight from Earth. When there are no planets (or when the orbital plane is not aligned appropriately), the star’s light curve is a straight line, since its brightness remains constant on the timescale of Kepler’s observations (a few years). If there is an exoplanet, the curve shows small U shaped dips, perfectly periodic, reappearing whenever the planet makes another transit. The duration, period and depth of these dips in the star’s light curve provide information about the planet, such as its size and temperature. Of the 150,000 stars observed by Kepler, only KIC 8462852 has a light curve that cannot, in all its details, be explained by known astronomical phenomena. Possibly, some new phenomenon that we do not yet know is responsible for this curve.

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This is precisely why it was not picked up by Kepler’s automatic exoplanet detection algorithm, which analyses the data in a first pass, but instead by amateurs who search through what we might call the “leftovers” of the automatic system. Boyajian’s Star shows irregular dips in brightness that occur at random times, each with different duration from a few hours to days or weeks and each time the drop in brightness is different: sometimes about 1%, sometimes an astonishing 22%! No planetary system can cause such extreme and varied fluctuations in a star’s brightness. As if all this were not enough, further study of the case after Boyajian’s publication revealed, in older archived astronomical data, that KIC 8462852 has dimmed by about 15% in the last 100 years!

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This was considered practically impossible, since once their formation is complete, stars maintain almost the same brightness for billions of years, and their luminosity changes significantly only shortly before they die, when they run out of nuclear fuel. Even those rapid changes occur on timescales of millions of years and are accompanied by specific characteristics which Boyajian’s Star does not show. This star, according to all other measurements, is an ordinary, middle aged star. It is neither a variable star nor a pulsating star with a stable period. There is no evidence that it is accreting material from an unseen stellar companion, nor that it has an abnormal magnetic field, nor that it is in the process of formation. If it weren’t for its unusual light curve, it would have nothing noteworthy to attract the attention of scientists.

Looking into the calibration data from Kepler before it went into full operation, it was found that even there, over four years, KIC 8462852 shows a 3% decrease in brightness.

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So astronomers must find explanations for two phenomena:

1. the gradual dimming of the star’s overall brightness, and

2. the strange, “irregular” short term dips in its luminosity.

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Although scientists would prefer a single explanation for both, each phenomenon is difficult to explain even on its own all the more so when the explanation of one must be consistent with the explanation of the other.

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Scientists have tried to give various explanations:

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1) A swarm of icy comet fragments in a highly eccentric orbit around the star.
However, the idea that fragments in such a swarm could exist in sufficiently high concentrations to cause a 22% loss of observed brightness has been challenged. Nor is there any sign of the infrared emission that would be expected from such comets as they are heated and cooled by the star.

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2) A large number of small bodies in a “tight formation” orbiting the star.
Spectroscopic studies, however, have not found any evidence of merged material, hot dense dust, or circumstellar matter from a planet that might have evaporated or exploded at a distance of a few astronomical units from the star. Again, we do not see the expected infrared emission from a debris disk.

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3) The presence of a cloud in interstellar space, or in the vicinity of our Solar System, partially intervening in the line of sight to KIC 8462852 as Kepler moves.

Although there are some issues here as well, this is a more likely explanation than the previous ones especially if what we are dealing with is an interstellar cloud.

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4) A change in brightness due to internal processes in the star, e.g. an impending polarity flip of its magnetic field. But stars this luminous do not show solar like magnetic fields, and such a field cannot explain the long term dimming. A variation on this idea suggests that Boyajian’s Star may relatively recently have absorbed a brown dwarf and is currently in the process of returning to its normal brightness.

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5) A more exotic possibility: the presence of a small black hole in orbit around it.
But there are several objections to this theory as well, even if it cannot be completely ruled out.

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6) And finally the most desired and most exotic explanation:
the presence of a megastructure around the star, constructed by some extraterrestrial civilization. This scenario will become more likely only when all astronomical explanations of the phenomena have been rejected, and it will be confirmed only if artificial radio signals are detected from that region. Wouldn’t it be beautiful and desirable to discover that technologically advanced civilizations do indeed survive and do not self destruct? The star KIC 8462852, whose name is the catalogue number in the Kepler Input Catalog, is not very far from us only about 1,280 light years away, in the constellation Cygnus.

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Wouldn’t we like to receive a signal from its inhabitants to break our loneliness? It would be a blessing. For this reason, and so as not to leave any loose ends unexamined, scientists have already pointed the Green Bank radio telescope toward Boyajian’s Star. The anticipated more precise distance measurement by ESA’s Gaia mission will allow some scenarios to be ruled out.

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Let us hope that the Dyson Sphere turns out to be real and not just a projection of humanity’s longing for companionship.

Chariton Tomboulidis, astronomer / astrophysicist.