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A team of astronomers has identified what they believe are 27 “candidate planets” orbiting binary star systems, using a radical new detection method.
Instead of spotting a planet crossing in front of a star, which has been the usual way of detecting new planet-like objects — known as the transit method — researchers looked for tiny changes in the timing of how two stars eclipse each other.
These tiny shifts in eclipse timing can reveal the gravitational influence of an unseen planet orbiting the system.
The study, published in the Monthly Notices of the Royal Astronomical Society and led by Margo Thornton, a PhD candidate at the University of New South Wales and SETI Institute researcher, analysed data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
A different way to find planets
Most known “circumbinary” planets — planets orbiting two stars, as seen in the iconic twin-sunset scene on the fictional planet Tatooine in Star Wars: A New Hope, part of the original trilogy — are found when they pass in front of one of their stars and dim its light.
But that only works if the system is perfectly aligned with Earth. If it is not, the planet is invisible to this method.
The new study instead exploits a phenomenon called apsidal precession — a gradual rotation of a binary star’s orbital path over time.
When a planet orbits a binary system, its gravitational pull causes a subtle but measurable shift in the timing of the eclipses the two stars create as they pass in front of each other.
By tracking these tiny timing shifts across years of data from NASA’s TESS space telescope, the team was able to detect planetary companions without ever directly observing the planets themselves.
“The calculation of precession was based on the change in the argument of periastron over time of the binary star, which can be determined by the exact timing of both primary and secondary eclipses,” the authors of the study explained.
What researchers found
The team studied 1,590 eclipsing binary star systems. In 71 of them, they saw signs of orbital changes that could not be explained by known physics effects alone.
In 36 cases, something extra seemed to be causing the effect — and in 27 of those, the most likely explanation is a planet-sized object.
A few orbit hot, large stars where planets are usually very hard to detect with traditional methods.
Before this, only around 18 circumbinary planets had been confirmed, making this a particularly rare discovery.
Why the discovery of these new planets matters
The discovery — and the method behind it — are significant because they could lead to the unconvering of many more planets that current techniques miss, especially in more complex systems.
It also gives scientists a broader picture of how planets form and survive around two-star systems.
“The findings of this work will allow us to robustly test formation theories, constrain migration histories, and understand long-term evolution of circumbinary systems,” the study continued.
The researchers also note that their sample represents only a tiny fraction of known eclipsing binaries, namely “the sample [they] analysed was only a small fraction of the 2 million EBs in Gaia’s catalogue”.
They suggest that expanding the search across the full dataset and combining it with longer observational baselines from TESS, could reveal many more systems in the future.