Astronomers have found a four-star system doing something that has never been confirmed before. The system, TIC 433545934, has two close pairs of stars orbiting each other. While each pair eclipses its own two stars, as usual, only one pair eclipses the other. A paper outlining the properties of this unique system was submitted to the arXiv preprint server on Aug. 13. It has been accepted for publication in the journal Astronomy & Astrophysics.
‘Nested’ systems
When three or more stars are gravitationally bound together, they tend to organize into stable orbits to avoid flying apart or colliding. In triple-star systems, two stars orbit tightly around each other (the “inner binary”), while a third star orbits much farther out. More complicated quadruple-star systems have four stars.
These can be either “3+1” systems, with three stars in a nested triple plus one more star orbiting even farther out, or “2+2” systems, with two separate pairs of stars. Each pair orbits tightly around itself, while the two pairs orbit each other at a much greater distance.
The focus of this study is 2+2 systems, in which both inner pairs happen to be “eclipsing binaries.” This means each pair is oriented so that, when observed from Earth, the two stars in each pair periodically pass in front of each other, causing a regular dip in brightness.
When astronomers observe both pairs at once, their light blends into a single, more complex pattern. Detecting them, however, can be tricky because astronomers cannot immediately tell whether the pairs are truly gravitationally bound as one four-star system or simply two unrelated pairs that happen to line up by chance from Earth’s perspective.
They confirm the gravitational binding through eclipse timing variations—synchronized wobbles in both binaries’ eclipse timing due to the presence of the other system.
Three dips
In this study, astronomers led by Tamás Borkovits of the Baja Astronomical Observatory in Hungary studied a 2+2 type star system called TIC 433545934 that shows this matching timing pattern, confirming the two pairs really are gravitationally bound. What’s more unique is that they also observed a rare event causing a “three-dipped” eclipse, where the two entire binary pairs are seen passing in front of each other.
This makes TIC 433545934 the first-ever confirmed 2+2 quadruple star system that shows both: synchronized eclipse timing and eclipse between the whole pairs. Combined, this makes it a uniquely well-proven example of this rare class of system.
Let’s call the two pairs of stars A and B. When the stars of pair B also periodically pass in front of both stars of pair A, one after another, it creates a rare “triple-dip” dimming event caught by NASA’s TESS satellite. The team found that, strangely, it only happens one way: “these extra events occur only once during an outer revolution, that is, binary A does not eclipse the stars of binary B” the team writes in the paper.
They explain this asymmetry through the shape of the outer orbit—the path the two pairs trace around each other is notably elongated rather than circular, with a geometry that lines up for one pair to pass in front of the other, but not both.
Pair A vs. pair B
Using TESS data and ground-based follow-up, astronomers mapped out the whole system. The inner pairs orbit every 1.4 and 2.1 days, while the full four-star system takes about 224.5 days to orbit itself.
The two pairs also turned out to be quite different from each other. Pair A consists of two closely matched, slightly aged stars. Pair B has one star that dominates over its much lighter companion. Despite this internal contrast, the entire four-star system is unusually flat, with all the orbits aligned to within about 2 degrees of one another.
Researchers note that confirming the system’s outer orbital period relied heavily on archival sky-survey data, since TESS itself captured only a single observation of the outer eclipse. Additionally, stellar mass estimates may carry uncertainties, as they explain, “These are statistical only and were generated without the use of RV [radial velocity] data which were not available.”
Overall, TIC 433545934 is a first-of-its-kind object, surpassing a similar candidate, KIC 5255552, which lacked equally robust confirmation. Astronomers say that in roughly 152 million years, the more massive star in each binary pair may grow large enough to overflow its “Roche lobe,” triggering mass transfer between the two stars and dramatically reshaping the whole system.
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Publication details
Tamás Borkovits et al, TIC 433545934: The first 2+2 type doubly eclipsing binary with extra, mutual eclipses, arXiv (2026). DOI: 10.48550/arxiv.2608.13034
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A 4-star system caught eclipsing itself in a way never seen before (2026, August 24)
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