For years, the star that would not stop flickering has baffled astronomers. Now, researchers say they may finally be closing in on an answer.
Tabby's Star, formally known as KIC 8462852, sits roughly 1,500 light-years away in the constellation Cygnus. Since 2016, this ordinary-looking star has dimmed and brightened in ways that make no sense. Some dips cut its light by more than 20 percent. The star also fades slowly over years, a pattern none of hundreds of comparable stars shows. At first, some scientists even wondered if alien megastructures could explain it.
But a study published in July in the Monthly Notices of the Royal Astronomical Society brings fresh clues. A team led by Cristina Madurga-Favieres at the University of Warwick used NASA's Transiting Exoplanet Survey Satellite, or TESS, to take a closer look. What they found was striking: a perfectly round, symmetric dip in the star's light lasting about 21 hours and reducing brightness by just over 1 percent. This kind of signal, called a transit, happens when an object passes in front of a star and blocks some of its glow.
The transit occurred on September 3, 2019, and had never been reported before. The team combined years of TESS data with new measurements of the star's radial velocity to estimate what might be causing it. Their analysis suggests a companion object orbiting the star roughly every three to four years. Its mass falls somewhere between 5 and 14 times that of Jupiter, with a radius about 1.7 times Jupiter's size. That places it right on the line between a giant planet and a brown dwarf, a failed star that never ignited hydrogen the way our sun does.
The find matters because it is the cleanest signal ever spotted around Tabby's Star. Previous dimming events were irregular and hard to explain. This one looks like a solid, single object doing exactly what orbital mechanics predicts. The team tested other ideas: a background star partly eclipsing it, a drifting dust cloud, or a swarm of comets. None fit the data as well as one compact companion.
If this companion is real, it could also explain the star's wild dimming fits. Its gravity might fling comets and debris into the star's neighborhood, where they shatter and create dust clouds that periodically block the star's light. That would solve a decade-long puzzle.
Next, the team hopes other telescopes will help confirm the finding. The James Webb Space Telescope and Hubble Space Telescope could study the object's atmosphere and help pin down its exact orbit. "The presence of a companion would explain why these bodies are driven to the vicinities of the star, breaking up, as it would orbitally perturb them," the researchers wrote.
It would be the first time a companion has been directly detected crossing in front of Tabby's Star. After nearly a decade of mystery, that would be a real breakthrough.