A team of astronomers has announced the discovery of a rare sextuple star system—six stars gravitationally bound and periodically eclipsing each other from Earth's view.
The Transiting Exoplanet Survey Satellite (TESS), launched two years ago to hunt for nearby exoplanets, has revealed another cosmic surprise: the intriguing six-star system TIC 168789840.
Located approximately 1,900 light-years from Earth, these stars appear as a single bright point from afar. Fortunately, their orbital plane aligns perfectly with our line of sight, producing observable eclipses each time one star passes in front of another. From any other vantage point, this complex system would remain hidden.
In a preprint published on arXiv (pending peer review), the researchers note this isn't the first six-star system identified—three others have been found previously. The most famous is Castor in the Gemini constellation, one of the brightest "stars" in the night sky at just 51 light-years away.
Castor was initially spotted as a binary in 1719 by English astronomer James Pound. By 1905, it was recognized as two close binaries orbiting a common center. In 1920, a third pair was discovered encircling the inner four, confirming its sextuple nature.
Other configurations exist, like ADS 9731, where four stars orbit a common center, with two forming a tight binary, totaling six stars.
"TIC 168789840 closely resembles the Castor system," the authors explain. It features two inner binaries: one pair orbits every 31 hours, the other every 38 hours, forming an "inner quadruple" that circles a common center every 3.7 years. Two outer stars orbit every 197 hours, with the full system completing a revolution roughly every 2,000 years.
No exoplanets have been confirmed yet, but astronomer Tamás Borkovits from Hungary's Baja Astronomical Observatory, a co-author, imagines a "very special night sky" for any inhabitants: "Two suns like on Tatooine, plus four bright stars dancing around."
Only the outermost binary might host stable planets; the inner quadruple rotates too closely, likely ejecting or consuming any forming worlds. The distant third pair, however, could harbor exoplanets, per Borkovits.
The formation of such intricate multi-star systems remains a mystery. This discovery provides key data to unravel it, and TESS may reveal more in the future, piecing together these cosmic puzzles.
