Only 70 light-years from Earth, a star called Kappa Tucanae A hosts one of astronomy’s strangest mysteries.
Around it swirls dust so scorching—more than 1,000 degrees Fahrenheit—that by all normal rules of physics, it shouldn’t exist.
This kind of hot dust should quickly burn away or be blasted out of the system by intense radiation. Yet it persists.
Astronomers at the University of Arizona may have finally discovered why.
Using advanced observations from the European Southern Observatory’s MATISSE instrument, they found a hidden companion star that swoops dangerously close to Kappa Tucanae A.
This discovery, published in The Astronomical Journal, is the highest-contrast detection MATISSE has ever achieved—giving scientists their first real “laboratory” for studying this mysterious hot exozodiacal dust.
Hot exozodiacal dust is made up of tiny grains, as fine as smoke, that orbit extremely close to stars. Its existence is one of the biggest puzzles in planetary science because dust this close should evaporate almost instantly.
If we see so much of it, it must either be constantly replenished or held in place by forces researchers don’t yet fully understand.
This mystery has serious implications. The same stars with hot dust are also top candidates for finding Earth-like planets.
NASA’s planned Habitable Worlds Observatory will need to block starlight to detect faint planets—but hot dust scatters light and can overwhelm the telescope’s sensitive instruments. Understanding where this dust comes from is essential for hunting habitable worlds.
The new observations of Kappa Tucanae A were collected between 2022 and 2024 using interferometry—a technique that links multiple telescopes to achieve the sharpness of a much larger instrument.
The research team originally aimed to track how the dust changed over time. Instead, they stumbled upon something entirely unexpected: a companion star moving along a wildly stretched, elliptical orbit.
This companion swings as close as 0.3 astronomical units from the main star—closer than Mercury is to the sun. Its extreme orbit sends it plunging through the star’s inner dust region before racing back out into space. According to the team, it is almost certain that the companion plays a major role in stirring up, replenishing, or redistributing the hot dust.
The discovery builds on decades of pioneering work at Steward Observatory in Arizona, which developed some of the world’s most powerful tools for detecting warm and hot dust around stars.
Their Large Binocular Telescope Interferometer revolutionized the field, producing the most sensitive dust measurements ever made. Now, researchers are preparing for a next-generation European nulling interferometer expected to be 50 times more sensitive.
With Kappa Tucanae A, astronomers now have a rare system where they can observe a companion star interacting directly with the dust. This opens the door to testing multiple theories—whether the dust is trapped by magnetic fields, supplied by comets, or shaped by entirely new physical processes.
The discovery also raises the possibility that many other hot dust systems may hide similar companions. With this new clue, researchers plan to re-examine stars previously thought to be single.
For Stuber and the team, the system’s surprise companion is not just interesting—it’s transformative. “We weren’t expecting to find this star at all,” he said. “Now we have a unique system that lets us explore one of astronomy’s most elusive mysteries.”
