Why are Tatooine planets rare? Blame general relativity

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By Robert Sanders, UC Berkeley News. 

Excerpt: Of the more than 4,500 stars known to have planets, one puzzling statistic stands out. Even though nearly all stars are expected to have planets and most stars form in pairs, planets that orbit both stars in a pair are rare. Of the more than 6,000 extrasolar planets, or exoplanets, confirmed to date — most of them found by NASA’s Kepler Space Telescope and the Transiting Exoplanet Survey Satellite (TESS) — only 14 are observed to orbit binary stars. There should be hundreds. Where are all the planets with two suns, like Tatooine in Star Wars? Astrophysicists at the University of California, Berkeley, and the American University of Beirut have now proposed a reason for this dearth of circumbinary exoplanets — and Einstein’s general theory of relativity is to blame. ...If a planet is orbiting the pair of stars, the gravitational tugs from the stars make the planet’s orbit precess, ...similar to the way the axis of a spinning top rotates ...in Earth’s gravity. The orbit of the binary stars also precesses, but ...The precession rate of the stars increases, but the precession rate of the planet slows. ...“Two things can happen: Either the planet gets very, very close to the binary, suffering tidal disruption or being engulfed by one of the stars, or its orbit gets significantly perturbed by the binary to be eventually ejected from the system,” said Mohammad Farhat, a Miller Postdoctoral Fellow at UC Berkeley and first author of the paper. “In both cases, you get rid of the planet.”... 

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