Planets With Two Suns Are Almost Impossible To Find — General Relativity May Be Why | Discover...

Planets with two suns have long captured the imagination of science fiction fans, thanks largely to Tatooine, the iconic desert world from Star Wars . Given what astronomers know about how stars and planets form, these worlds should be common. Most stars are born with planets, and many stars form in pairs.

Yet when scientists look to the sky, planets orbiting two stars at once are surprisingly scarce. Of the more than 6,000 exoplanets discovered so far — largely by NASA's Kepler Space Telescope and the Transiting Exoplanet Survey Satellite (TESS) — only 14 are known to orbit binary star systems, which is far fewer than expected.

Now, astrophysicists writing in The Astrophysical Journal Letters believe they know why: the missing planets may be casualties of a subtle but powerful effect Albert Einstein predicted more than a century ago. “You have a scarcity of circumbinary planets in general and you have an absolute desert around binaries,⁘ said first author Mohammad Farhat in a press release . “Planets form from the bottom up, by sticking small-scale planetesimals together.

But forming a planet at the edge of the instability zone would be like trying to stick snowflakes together in a hurricane,” added Farhat. The problem doesn't stop with instability alone. Both the planet's orbit and the orbit of the two stars slowly rotate over time in a process known as precession — similar to how a spinning top wobbles as it slows down.

The planet's orbit precesses due to the stars' gravitational pulls, while the binary stars' orbit precesses largely because of relativistic effects. As tidal interactions gradually shrink the stars' orbit, the precession rate of the stars speeds up, while the planet's rate slows down. When these rates match, the system enters a resonance that stretches the planet's orbit into an extreme oval.

The key insight of this new research is the role played by Einstein's general theory of relativity . Proposed in 1915, the theory describes gravity not as a force, but as a bending of spacetime itself, often compared to the way a heavy object warps a trampoline. Related materials: Visit website