Extremely Elliptical Eclipsing Binaries

Variable stars are, as their name suggests, stars whose brightness varies over time in a periodic way. There are only three options:

  • The star is a Cepheid variable (type 1 of type 2), stars that due to a cycle of ionising and doubly ionising helium vary in brightness.
  • The star is an RR Lyrae variable, the same as a Cepheid variable but in the infra red spectrum.
  • Or the star is part of a binary system, called binary eclipsing stars.

This last one is very interesting. When the two suns are orbiting each other so long as their movement is in a plane with the Earth there will come a time when they block the line of sight to each other. It is unlikely that both stars will be of equal size and so when the small star obscures only part of the bigger twin we see a dip in light and when their rolls are reversed the completely eclipsed smaller star results in a bigger dip. Of course there are many variations and unique situations when it comes to eclipsing binary systems.

The Kepler missions have recently brought back information of eclipsing binary stars with incredibly eclipsed orbits. The stars get only a few solar radii away from each other at perihelion (closest point) to nearly fifteen times this at aphelion (farthest point). Their proximity results in both stars distorting out of their normally spherical shape.  This has resulted in luminosity time graphs resembling saw tooth wave rather than a classic sinusoid:

Image result for sawtooth wave
Thank you to Erik Cheever from swarthmore.edu for this image.

The real mystery is how these stars have managed to maintain this cycle for so long. Distorting the shape of a sun isn’t easy and it should have damped the system into having a circular orbit in less than a hundred cycles. There are ideas being investigated that perhaps a third sun is lending a hand to maintaining the distorted orbit. Observations are being made to try and locate this “third man” of these systems but none have managed to locate the hidden sun yet.


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