This May Be the Best Alternative Explanation to That Extraterrestrial Dyson Sphere So Far

Monday, 26 October 2015 - 11:44AM
Astrobiology
Astronomy
Alien Life
Monday, 26 October 2015 - 11:44AM
This May Be the Best Alternative Explanation to That Extraterrestrial Dyson Sphere So Far
Within the next week, astronomers are expected to have an answer regarding the cause of the bizarre, irregular dips in brightness of star KIC 8462852, which have led many to speculate that we've found long-sought evidence of an alien civilization. Now, space blogger Jim Galasyn has an alternative explanation: the star itself is oblate, or lopsided, leading to the asymmetrical blockages of light.

While many stars experience dips in brightness as a result of the transit of other celestial objects, the dips of this particular star were unusual for being more extreme (up to 22%), asymmetrical, and non-periodic. The best explanation that involved a natural phenomenon was a string of comets circling the star, but this explanation is considered to be inadequate to fully explain the evidence. As a result, the astronomers who discovered the star began to look into the (admittedly remote) possibility of a Dyson sphere, or a megastructure built around the star by an advanced alien civilization.

The investigation is underway, and we're expected to receive answers by the end of this week. But in the meantime, Galasyn of Desdemona Despair has an alternative explanation from a 2013 paper by Barnes et al. called "Measurement of spin-orbit misalignment and nodal precession for the planet around pre-main-sequence star PTFO 8-8695 from gravity darkening." According to this paper, some stars don't have uniformly spinning discs, which causes the radius to be larger at the equator than at the poles. Since the poles have smaller surface area, they have higher surface gravity, which causes the poles to be "gravity brightened" and the equator to be "gravity darkened."
Opening quote
When a star is oblate, it has a larger radius at its equator than it does at its poles. As a result, the poles have a higher surface gravity, and thus higher temperature and brightness. Thus, the poles are "gravity brightened", and the equator "gravity darkened".

The star becomes oblate (and hence gravity darkening occurs) because the centrifugal force resulting from rotation creates additional outward pressure on the star.
Closing quote

Since there is variable brightness in different areas of the star, the irregular curves of light could be explained by planetary bodies moving across these brighter and darker areas. As planets of different sizes passed across different parts of the star, the brightness would change in asymmetrical and irregular ways. 

Opening quote
"Did Kepler discover evidence of an extraterrestrial civilization?" Galasyn wrote on his blog. "Before we invoke aliens, we should consider the plausible natural explanation provided by Barnes:

'An oblique transit path across a gravity-darkened, oblate star leads to the long transit duration and asymmetric lightcurve evident in the photometric data.'"
Closing quote
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