For a little while, we were the only people on Earth who knew about it.
For generations, astronomers have charted the cosmos almost exclusively through the lens of single-star systems, leaving the majority of stellar arrangements — binary pairs — largely unread. A team at UNSW has now introduced a method that listens not for a planet's shadow crossing a star, but for the subtle gravitational whisper it leaves in the orbital conversation between two stars, yielding 27 new circumbinary planet candidates from a single study. Published in the Monthly Notices of the Royal Astronomical Society and drawn from NASA's TESS data, the findings suggest that the universe's planetary architecture is far richer and stranger than our Earth-bound vantage point has allowed us to see. What we have confirmed, it seems, is not a census but a footnote.
- Only 18 circumbinary planets had ever been confirmed before this study — a number so small it barely constitutes a category, let alone a map of the cosmos.
- Traditional transit detection is blind to planets whose orbits don't align with our line of sight, meaning entire populations of worlds have been hiding in plain statistical sight.
- The new apsidal precession method tracks how two stars eclipse one another over time, and when those eclipses drift in ways physics alone cannot explain, a planet is the most likely culprit.
- Applied to just 1,590 binary systems in TESS data, the method surfaced 27 candidates — ranging from Neptune-mass to ten times Jupiter's mass — suggesting a roughly 2% occurrence rate that could imply tens of thousands more across the galaxy.
- The team is now using spectral analysis at the Anglo-Australian Telescope to rule out stellar remnants and confirm which candidates are true planets, with future surveys like the Vera C. Rubin Observatory poised to expand the search by orders of magnitude.
For decades, the circumbinary planet — a world orbiting two stars — existed more vividly in science fiction than in confirmed science. Only 18 had ever been verified, a scarcity that had less to do with cosmic rarity and more to do with the limits of how we look. Nearly every known exoplanet was found through the transit method, which requires a planet's orbit to align precisely with our line of sight from Earth. Worlds tilted at the wrong angle, or tracing irregular paths, remained invisible.
A team at UNSW has now found a way around that blind spot. Their method, called apsidal precession, doesn't watch for a planet's shadow — it watches the stars themselves. By tracking how two stars eclipse one another over time, researchers can detect when those eclipses drift off schedule in ways that only an unseen gravitational influence can explain. Applied to NASA's TESS satellite data across 1,590 binary star systems, the method surfaced 27 candidate circumbinary planets in a single study, published in the Monthly Notices of the Royal Astronomical Society.
Lead author Margo Thornton, a PhD candidate just one year into her doctoral work, describes the quiet electricity of the discovery's first moment — when the data from the first system she examined pointed unmistakably toward a planet, and she and her colleagues were briefly the only people on Earth who knew. The 27 candidates span a wide range, from roughly Neptune-sized to ten times Jupiter's mass, and lie between 650 and 18,000 light-years away across both hemispheres of the sky.
What makes the findings significant is not just the number but the rate: 27 candidates from fewer than 1,600 systems suggests a roughly 2% occurrence rate. Since binary and multiple star systems outnumber single stars in the universe, the implication is that thousands — perhaps tens of thousands — of circumbinary planets are waiting to be found. 'We've painted half a picture, and the other half of the canvas is completely blank,' says senior astronomer Ben Montet.
Thornton's next step is confirmation. Using the Anglo-Australian Telescope in Coonabarabran, she will analyze the light spectra of the binary stars to rule out stellar remnants — brown dwarfs, white dwarfs, black holes — as alternative explanations. Whatever cannot be explained away becomes a confirmed world. Future instruments, particularly the Vera C. Rubin Observatory, could extend the method to vastly larger samples. For now, the candidates remain unconfirmed, but the universe they hint at is already more complex than the one we thought we knew.
For decades, astronomers have known that planets orbiting two stars instead of one should exist somewhere in the cosmos. Yet we've confirmed only 18 of them. The most famous circumbinary planet remains entirely fictional: Tatooine, the desert world where Anakin Skywalker was born, rendered in the Star Wars films as a place where two suns hang perpetually in the sky.
A team at UNSW has now upended that scarcity. Using a detection method called apsidal precession, researchers identified 27 candidate circumbinary planets in a single study, published in the Monthly Notices of the Royal Astronomical Society. The work suggests that what we've found so far represents only the smallest fraction of what's actually out there.
The breakthrough hinges on a fundamental shift in how astronomers search for distant worlds. Nearly all known exoplanets have been discovered through the transit method: watching for the telltale dip in starlight when a planet crosses in front of its host star. But this approach works only when a planet's orbit aligns with our line of sight from Earth. Countless worlds orbiting at different angles, or in irregular paths, remain invisible to us. "We're missing a huge part of the architecture for these systems," says Ben Montet, a senior astronomer on the study.
Apsidal precession works differently. It monitors the orbital dance between two stars themselves, tracking how their eclipses of one another shift over long periods. When those eclipses deviate from their expected schedule in ways that can't be explained by physics alone, something else is tugging at the system—likely a planet. The team applied this method to data from NASA's Transiting Exoplanet Survey Satellite, a space telescope launched in 2018 to hunt for exoplanets. The results surprised even the researchers. "I wasn't expecting to find 27 already at this point from the pilot study," Montet says.
Margo Thornton, a PhD candidate at UNSW and lead author of the study, made the discoveries just one year into her doctoral work. She describes the moment of realization: when the first system she examined showed clear signs of stellar precession, and every other explanation fell away, she and her team were briefly the only people on Earth who knew they might have found a planet. "For a little while, we were the only people on Earth who knew about it," she recalls. "It was a very exciting feeling."
The 27 candidates range in mass from roughly Neptune-sized objects to bodies ten times as massive as Jupiter. They scatter across both northern and southern skies, positioned between 650 and 18,000 light-years away. What matters most is the detection rate itself: the team found these candidates in just 1,590 binary star systems examined, suggesting a roughly 2% occurrence rate. If that holds across the broader universe, thousands or even tens of thousands of circumbinary planets may be waiting to be found.
This matters because binary and multiple star systems vastly outnumber single-star systems like ours. More than half the stars in the universe orbit companions. Yet nearly all our knowledge of planetary systems comes from studying the minority—single-star configurations. "We've painted half a picture, and the other half of the canvas is completely blank," Montet says. Understanding how planets form and survive in these alien environments could reshape our understanding of where life might exist.
Thornton and her team are now working to confirm which candidates are genuine planets. She will study the light spectra of the binary stars using the Anglo-Australian Telescope in Coonabarabran, a facility accessible remotely from UNSW's campus. Spectral analysis can rule out whether the detected objects might be stellar remnants—brown dwarfs, white dwarfs, or black holes—rather than planets. If nothing else explains them, they become confirmed worlds. The team also plans to apply the same method to larger samples and run simulations to understand how these planets might have formed and evolved. Future surveys, particularly the Vera C. Rubin Observatory's Legacy Survey of Space and Time, could reveal orders of magnitude more. For now, the real-life Tatooines remain candidates. But the universe, Thornton suggests, is far more complex than we can directly see.
Citas Notables
We're missing a huge part of the architecture for these systems— Ben Montet, UNSW astronomer
If circumbinary planets do turn out to be habitable, that means life could be anywhere. Life could be everywhere.— Ben Montet
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that we find planets around binary stars specifically? Aren't they just more planets?
Because they tell us something fundamental about where planets can exist. More than half the stars in the universe have companions. If we only study single-star systems, we're ignoring the majority of the cosmos.
But these are just candidates right now. How confident are you they're actually planets?
Confident enough to pursue them seriously, but not certain. The apsidal precession signal is real—the orbital wobble is there. What we need to rule out is whether something else, like a brown dwarf or stellar remnant, is causing it instead of a planet.
The distances are staggering. The closest is 650 light-years away. Why does that distance matter for this work?
It doesn't change the method itself, but it does mean we can't visit or image these worlds directly. We're inferring their existence from gravitational effects. The distance is almost irrelevant to the physics.
You mentioned being the only person on Earth who knew about the first signal. What was that like?
It's hard to describe. You're looking at data, and suddenly you see something no one else has seen yet. There's a kind of responsibility in that moment—you have to be absolutely sure you're not making an error.
What happens if some of these turn out to be habitable?
Then we have to completely rethink where life could exist. If planets can form and persist in these chaotic two-star systems, and some are in the habitable zone, then life could be far more common than we thought. That changes everything.
How many more of these do you think are actually out there?
Based on our 2% detection rate, potentially tens of thousands. But that's just in our galactic neighborhood. The real number across the entire universe could be astronomical.