Tuesday, 20 October 2015

The Mystery of KIC 8462852

Just a couple of days ago, a paper was published in the MNRAS journal, and quite frankly it's one of the most interesting astronomy papers of recent years. The findings are so bizarre, the possibility of aliens being involved has been raised...

OK, so aliens are unlikely, but something odd has been found orbiting KIC 8462852. The star was observed as part of the Kepler mission to find exoplanets, and the strangeness of this particular star was found through the Planet Hunters Zooniverse project (which the public can get involved with). 

The transit method was used to measure the dips in intensity of light when exoplanets cross the face of a star along our line of sight. In most cases, such light curves are smooth and periodic (with a time period equal to the orbital period of the eclipsing planet). However, this star showed a bizarre light curve which was (a) not periodic and (b) extremely deep. The deepest transit blocked 20% of the stellar flux - this is a ridiculous amount! Planets tend to be so much smaller than their parent stars that normally a 1% drop is considered large. Also, planets go round in nice Keplarian orbits, obeying Newtons laws... but this leads to periodic transit events. 

So how can we explain the odd light curve, shown below?

Well firstly, the non-periodicity suggests one of two things. Either the object is large and irregular in shape, or there are in fact many small objects, perhaps in clusters, for example 'swarms' of comets. Errors in the optics have been ruled out, the light curve really is like this and there isn't a mistake. The possibility that the star itself is unstable has been considered, and although some stars do pulsate, they too are periodic - furthermore KIC 8462852 is a main sequence star, like our Sun. So this scenario seems unlikely too.

We are left, realistically, with two possibilities. 

1 . The star is being orbited by a huge alien construction of some kind. Daft as this sounds, SETI (Search for Extra Terrestrial Intelligence) have actually turned their radio telescopes towards KIC 8462852, just in case!

2. The star is being orbited by huge (and we mean HUGE) clouds of exocomets. This could reproduce the light curve, if the distribution of comet clouds around the star were irregular.

The latter seems the most plausible. Further observations will be made, but in truth either answer would be extraordinary. The team have looked through the entire Kepler data set and have found only a few remotely similar light curves, but KIC 8462852 stands out even among these as particularly strange. If one star is surrounded by comet clouds, why don't we see many like this? Whatever the answer, we're sure to learn something new from the curious case of KIC 8462852...

Reference: "Planet Hunters X, KIC 8462852 - Where's the flux?", Boyajian et al, (2015), MNRAS

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