'Wide-set' twin stars can drive dirtball companions WILD, insist boffins

Distant hot companions fling planets into space

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Astrophysicists researching planets within the systems of binary stars - where one star orbits another - have found that the further apart the stellar twins are, the more their planetary systems are susceptible to violent disruptions. In simulated scenarios, distant binary star systems flung away the planets under their influence, sending them spinning off into the blackness.

Stars in binary star systems where the stars are set far apart are more likely to develop eccentric, noncircular, orbits of each other, explained researcher Nathan Kaib, of Northwestern University and the University of Toronto, in an article published in Nature today. This meant that the orbit could become elliptical, with the second star sometimes passing very close to the first, wreaking havoc on planets circling it.


Still from video simulation of planetary system with a wide binary star. Credit Nathan Kaib

Kaib explained why these twin stars' orbits became eccentric:

The stellar orbits of wide binaries are very sensitive to disturbances from other passing stars as well as the tidal field of the Milky Way. This causes their stellar orbits to constantly change their eccentricity – their degree of circularity. If a wide binary lasts long enough, it will eventually find itself with a very high orbital eccentricity at some point in its life.

The research simulated a hypothetical planetary system similar to our own. The researchers added a distant twin star to the Sun and trialled what would happen to the planets at the edge of our solar system under its influence. In almost half of all simulations at least one of the four gas giants on the edge of our solar system gets forcibly ejected from orbit, in some two are shaken off and ping off into space. In the scenario viewable here on the Uni Toronto website, both Neptune and Uranus are ejected from solar orbit.

Researchers measured the orbits of planets that circle distant binary stars and found that they are markedly more erratic than ones with a single star such as in our own solar system.

"This process takes hundreds of millions of years if not billions of years to occur in these binaries. Consequently, planets in these systems initially form and evolve as if they orbited an isolated star," said Kaib. "It is only much later that they begin to feel the effects of their companion star, which often times leads to disruption of the planetary system."

There was some reassurance for Earthlings though: planets as close to a star as the Earth is to the Sun were not significantly affected by rogue twin stars, even when the twin's orbit was wildly erratic. Planets that are 10 times as far away as Earth were vulnerable. ®

"Planetary system disruption by Galactic perturbations to wide binary stars" by Nathan A Kaib, Sean N Raymond & Martin Duncan was published in Nature on 6 January, 2012

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