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Of more than 6 thousand known exoplanets, only 14 orbit two stars — and a study published in the Astrophysical Journal Letters shows that Einstein’s general relativity destabilizes these orbits and expels the planets into space
Almost half of Sun-like stars exist in pairs — these are called binary stars, two suns orbiting each other.
If double stars are so common, planets orbiting two stars should be too.
But they are not.
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Of the more than 6,000 exoplanets cataloged by 2025, only 14 are circumbinary — meaning they orbit two stars at the same time.
It’s an absurdly low number.
According to a study published in December 2025 in the Astrophysical Journal Letters, the explanation may lie in Albert Einstein’s theory of general relativity.
“There is a general scarcity of circumbinary planets and a true void around very close binary systems,” said Farhat, the study’s lead researcher.
How Einstein explains the disappearance of planets
In a binary system, the two stars exert complex gravitational forces on any surrounding planet.
General relativity predicts an effect called orbital precession — a slow and continuous change in the orientation of the orbit.
In very close binary stars — those that orbit each other in less than 7 days — this precession becomes too strong.
The planet’s orbit becomes unstable.
The planet begins to oscillate, gains energy, and ends up being expelled into space.
According to the study’s calculations, about 8 out of 10 planets lose orbital stability over time in these systems.
It’s like trying to balance a marble on top of two spinning bowling balls — sooner or later, it gets thrown off.
The search for planets like Tatooine
The two-sun scenario in the sky became famous in the Star Wars movie, on the fictional planet Tatooine.
When the Kepler telescope was launched in 2009, scientists expected to find hundreds of real “Tatooines”.
Kepler monitored thousands of eclipsing binary stars — systems where one star regularly passes in front of the other.
These systems are ideal for detecting planets by transit.
But the results were disappointing.
The first confirmed circumbinary planets, such as Kepler-34b and Kepler-47c, appeared between 2011 and 2012.
After them, detections practically stopped.
No circumbinary planet has been found around very close binaries — a complete void.
Planets that are born far away and migrate to their doom
Scientists believe that circumbinary planets form in disks of gas and dust far from the stars.
Then, they migrate to closer orbits.
However, upon getting too close to the two stars, they enter the zone of gravitational instability.
According to Dr. Leinhardt, from the University of Bristol: “Our simulations show that the circumbinary disk is a hostile environment even for large, strongly gravitating objects.”
The few survivors — like the 14 known ones — orbit just beyond the dangerous zone.
They are the lucky ones who stopped in the right place.
The TESS telescope continues the search
The TESS (Transiting Exoplanet Survey Satellite) satellite, Kepler’s successor, has confirmed new circumbinary planets such as TOI-1338b.
The Zooniverse project “Eclipsing Binary Patrol,” led by Veselin Kostov of NASA, recruits volunteers to analyze TESS data.
But even with more advanced technology, detections remain rare.
The rarity is not an equipment problem — it’s a physical reality.
Einstein predicted over a century ago that gravity curves spacetime. The consequences for planets in double stars are only now being fully understood.
What this means for the search for life
If planets with two suns are rare, habitable candidates in this type of system are extremely rare.
The habitable zone — the range of distance where liquid water can exist — is more complicated in binaries.
Temperature fluctuates as the two stars approach and recede.
For astrobiology, the study suggests that the search for life should focus on more widely separated binaries, where relativistic precession is weak.
Or on solitary stars like our Sun, where planets have stable orbits for billions of years.
The numbers in perspective
To understand the rarity, just compare:
- 6,000+ exoplanets known in total
- ~50% of Sun-like stars are binaries
- 14 confirmed circumbinary planets — 0.2% of the total
- 0 planets in binaries with an orbital period less than 7 days
- 80% of planets that form near binaries are expelled
The Universe has billions of double stars, but almost no planet can survive among them.
What could still change
The sample of 14 planets is small, and there may be detection bias.
Transits in binaries require specific alignments, which makes observation more difficult.
The James Webb Space Telescope (JWST) may reveal new candidates in the coming years.
Furthermore, Newtonian instability — without relativity — also contributes to the problem.
General relativity is a factor, not the only one.
But it’s the missing piece to explain the complete void in close binaries.
Einstein, once again, was right — even about planets he never saw.
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