Planetas that orbit two suns at the same time appear frequently in science fiction. In the real universe they are rare.
Entre more than 6 thousand exoplanets have already been confirmed, only 14 orbit systems formed by two stars. The number is well below what astronomers expected to find when considering how many stars there are in pairs.
Pesquisadores of Universidade of Califórnia in Berkeley, in Estados Unidos, and Universidade Americana of Beirute, in Líbano, published a study in December 2025 in the magazine The Astrophysical Journal Letters. Eles investigated what could cause this shortage. The calculations indicate that effects predicted by Albert Einstein’s theory of general relativity contribute to making the orbits of these planets unstable over time.
Precessão orbital affects stability of circumbinary worlds
In binary systems, the two stars orbit each other. A planet that revolves around both suffers the combined gravitational influence of the two stars. Essa force causes the orientation of the planet’s orbit to slowly change, a phenomenon known as orbital precession.
The same process occurs with the stars themselves. Parte of this change in orientation comes from general relativity. Over millions of years, tidal interactions between stars cause the distance between them to gradually decrease.
Essa approximation changes the speed at which stars revolve around each other. Mathematical and computer simulation models show that the precession caused by general relativity gains strength in this scenario.
The result is a resonance that increases the eccentricity of the planet’s orbit. The trajectory becomes increasingly elongated.
- The planet could be ejected from the system completely.
- Ele could get too close to one of the stars and experience tidal disruption.
- In many cases, the planet ends up swallowed by one of the stars.
Researchers estimate that relativistic effects destabilize about eight out of ten planets in tight binaries. Desses, around 75% would be destroyed in the process.
Sistemas tight binaries form a clear instability zone
Binárias with an orbital period of seven days or less concentrates most of the observed eclipsing systems. São It is precisely in these cases that the scarcity of circumbinary planets becomes more evident. Astronomers call this region the planetary desert.
Doze of the 14 known circumbinary planets orbit just beyond this zone of instability. Isso suggests that many of them formed further away and migrated inward later. Formar a planet close to the unstable boundary would be extremely difficult.
Models show that the combination of general relativity and tidal orbital shrinkage clears the region near tight binaries. Planetas that manage to survive stay in wider orbits, where relativistic effects are less intense.
Descoberta reinforces understanding of planet formation in multiple systems
Most known exoplanets have been detected by transit or radial velocity. Ambos methods work best when the planet orbits a single star. Sistemas binaries complicate observations because the two stars generate more complex signals.
Mesmo thus, the low count of circumbinary planets has drawn attention since the first years of operation of the Kepler telescope. Astronomers expected hundreds of cases. Instead, they found a small fraction.
The study provides a theoretical explanation that aligns with observational data. Ele does not rule out other factors, such as detection difficulties or different formation processes. But it does indicate that orbital dynamics influenced by general relativity play an important role in the rarity of these worlds.
Comparação with science fiction highlights contrast with observed reality
Mundos as Tatooine, of Star Wars, inspired generations of viewers with the idea of a planet illuminated by two suns. In practice, the universe shows that stable conditions for this type of configuration are uncommon.
The 14 confirmed cases serve as valuable exceptions. Eles allow scientists to test models of planetary formation and evolution in complex environments. Future Observações with more sensitive telescopes may reveal whether circumbinary planets exist in greater numbers in regions further away from binaries.
The work helps refine expectations about how many habitable or interesting planets might exist in multiple systems. Ele also reinforces how general relativity, a theory from 1915, remains relevant for interpreting current astrophysical phenomena.
What the numbers reveal about exoplanets in binaries
- Mais of 6 thousand confirmed exoplanets in total.
- Apenas 14 orbits two stars simultaneously.
- Most of the known 14 lie outside the tight binary instability zone.
- Modelos indicate that 80% of nearby planets would be destabilized by general relativity.
- Cerca than 75% of the destabilized planets would be destroyed.
Esses data comes from observations accumulated by missions such as Kepler and TESS, cross-referenced with recent theoretical simulations.
Próximos steps in the search for planets in binary systems
Astrônomos plan to continue monitoring known binaries with high-precision instruments. The goal is to detect more candidates and confirm stable orbits at greater distances.
Estudos like this also guide the interpretation of data from future space telescopes. Entender instability mechanisms help distinguish between actual absence of planets and detection limitations.
Research published in December 2025 paves the way for more accurate models on the evolution of multiple planetary systems. Ela shows how subtle forces, predicted more than a century ago, shape what we observe in the cosmos today.