Last week a star about 1400 light years away made some headlines with its unusual characteristics. That it garnered attention from SETI (Search for Extra-Terrestrial Intelligence) and many in the astronomy community, is noteworthy. That it made mainstream media is telling of humanity’s obsession with ‘aliens.’
The star, KIC 8462852, like many other stars, was under observation by the Kepler Space Telescope to detect variations in brightness. Why do that? When a planet moves in front of a star, it blocks a little bit of that star’s light from reaching us. That causes the star to dim a little – usually on the order of about 1-2%. In other words, Kepler is looking for planets, specifically Earth-like planets. To date it has confirmed more than 1000 planets in nearly 450 star systems.
So what makes KIC 8462852 so special?
To the left is a depiction (composite of images from JPL libraries) of the planet Kepler 7b. I picked this planet to make a comparison because it is a similar distance away from Earth (1000-1400 light years) and is pretty big – comparable in size to Jupiter (about 1.5 times as large) – so there is reference. It is also interesting in that it was the first exoplanet to have clouds identified on it. It orbits very close to its sun – only about 5% as far away as Earth is from Sol. Below is a chart showing the dip in the light coming from the Kepler 7 star when Kepler 7b moves in front of it. You can see that once every three days or so, the chart drops by about 2.5% (the dips shown on the magenta line).
Chart showing dimming of the star Kepler 7 by planet Kepler 7b – data source NASA JPL
Now let’s look at the same chart for KIC 8462852, also known as Tabby’s Star.
Image credit: Boyajian et al.
That’s quite a difference! There are a number of very small dips, then every 800 days or so, the light from the star dims more, not just by a couple percent, but by as much as 22%! (the second dip). That much light being blocked can’t be due to a planet. It would simply be too big. So what could it be?
Here are some possibilities:
Aliens
Yes, I said aliens. Some more pragmatic people out there might be asking how an ex-NASA engineer could be so out there to suggest that intelligent aliens exist. I might counter that how could any pragmatic person not believe that aliens exist somewhere out there. There are billions of star systems in each of billions of galaxies. Considering that we’re likely to find extraterrestrial life in our own star system, the idea that there could be no life outside it is simply absurd. Then the idea that none of that life could ever become sentient, intelligent life is also absurd. There are simply too many star systems with too many planets. So if it is aliens, why does the star dim? One theory is that they’ve built a Dyson Sphere, a massive solar array around a star that captures much of its energy. If the sphere was complete, you wouldn’t see the dimming events, so I discount that. Maybe it’s only part of a Dyson Sphere near an alien planet – it’s in the process of being built. Or perhaps it’s a massive shield built to help protect the planet from an abrupt change in the star’s characteristics. Maybe it’s a ringworld like the one brought to life in Larry Niven’s amazing novel of the same name. This too, I’m not so sure about. The ring rotates around a star in a manner that would likely not cause dimming as seen by Kepler. The main reason I’d discount the Dyson Sphere (or partial) theory is that if a race of intelligent beings has the capability to build one then they probably have mastered a more efficient power source like fusion or antimatter, making a Dyson sphere obsolete.
A Massive Cloud of Debris or Dust
Another theory is that a huge debris cloud is orbiting the star and every 800 days or so it moves between the star and us and blocks some light. On the surface this could make sense, but why hasn’t the dust coalesced into a planetary body or spread into a circumstellar disk? Where did it come from? And if it were a cloud of debris, it would have to be huge. Remember that a planet half again larger than Jupiter caused a dimming of its star by only a couple percent. Again, the largest amount of dimming here was nearly ten times that at 22%. Yet there is another star relatively nearby that could be influencing things, so there’s another variable thrown into the mix.
Something Odd About the Star Itself
Many celestial bodies can become what is called ‘oblate.’ An oblate object spins so fast that it sort of flattens out – Saturn does this to some degree. When this happens you see what is called ‘gravity darkening’ occurring – along with the opposite: gravity brightening. Basically, more surface gravity is present near the poles so you more pressure and thus more heat and light. The opposite is true around the equator. So one theory is that planets are moving in front of brighter areas at certain times which correspondingly dims the star more than the same planet would for a more spheroid star. I can sort of buy this, but the magnitude of change is so huge that it doesn’t seem to fit. One of the more odd things about the data is that nothing is as expected. When a planet passes in front of a star, the dimness is relatively symmetrical on the approach and retreat of the planet. Look at the graph below that’s a close-up of the chart of KIC 8462852 where the second dip occurs – actually it’s a series of dips. The two larger dips (circled in red) are distinctly non-symmetrical. There is one in the middle (green), however, that looks pretty darned symmetrical to me. It is also only about a 3% drop – within the realm of reason for a large planet. Could this be a planet passing by? Maybe, except that planets look like the inset image (outlined in blue), whereas the dip in question has those little mini-dips on each side. Just more weirdness.
Is it aliens? I’m not going to say that. Is it a dust or debris field? I’m not going to say that either. Is it something weird within the star? Nope, I’m not going to say that either. There isn’t enough evidence to prove or rule out any of those explanations. The bottom line is that something very interesting and different is occurring at KIC 8462852. There is enough credence for the alien theory that the Allen Telescope Array is investigating the star system for anything that might betray intelligent life. Some findings could be out later this week.
UPDATE (11/8/2015):
The Allen Telescope Array has not picked up any radio signals coming from KIC 8462852. That in itself does not rule out the presence of intelligent life in that system. What still remains is that something very strange and different is occurring at Tabby’s Star.
Headline photo credit: NASA
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