From Newsgroup: sci.misc

From the -2Tatooine-+ department:
Title: Why Are Tatooine Planets Rare? Blame General Relativity
Author: admin@soylentnews.org
Date: Tue, 24 Feb 2026 02:37:00 +0000
Link: https://soylentnews.org/article.pl?sid=26/02/23/0050217&from=rss

hubie[1] writes:

Astronomers have found thousands of exoplanets around single stars, but
few around binary stars rCo even though both types of stars are equally
common. Physicists can now explain the dearth[2]:

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 rCo most of them found by NASA's Kepler Space Telescope and the Transiting Exoplanet Survey Satellite (TESS) rCo 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 rCo and Einstein's general theory of relativity is to blame.

In most binary star systems, the stars have similar but not identical
masses and orbit one another in an egg-shaped or elliptical orbit. If
a planet is orbiting the pair of stars, the gravitational tugs from
the stars make the planet's orbit precess, meaning the orbital axis
rotates similar to the way the axis of a spinning top rotates or
precesses in Earth's gravity.

The orbit of the binary stars also precesses, but mainly because of
general relativity. Over time, tidal interactions between the binary
pair shrink the orbit, which has two effects: The precession rate of
the stars increases, but the precession rate of the planet slows.
When the two precession rates match, or resonate, the planet's orbit
becomes wildly elongated, taking it farther from the star but also
nearer at its closest approach.

"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."

That doesn't mean that binary stars don't have planets, he cautioned.
But the only ones that survive this process are too far from the
stars for us to detect with transit techniques used by Kepler and
TESS.

"There are surely planets out there. It's just that they are
difficult to detect with current instruments," said co-author Jihad
Touma, a physics professor at the American University of Beirut.

[...] Farhat points out that binaries have an instability zone around
them in which no planet can survive. Within that zone, the three-body interactions between the two stars and the planet either expel the
planet from the system or pull it close enough to merge with or be
shredded by the stars. Peculiarly, 12 of the 14 known transiting
exoplanets around tight binaries are just beyond the edge of the
instability zone, where they apparently migrated from farther away,
since planets would have a hard time forming there.

"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," he said.

Read more of this story[3] at SoylentNews.

Links:
[1]: https://soylentnews.org/~hubie/ (link)
[2]: https://news.berkeley.edu/2026/01/30/why-are-tatooine-planets-rare-blame-general-relativity/ (link)
[3]: https://soylentnews.org/article.pl?sid=26/02/23/0050217&from=rss (link) --- Synchronet 3.21d-Linux NewsLink 1.2