A binary star system called V Sagittae is on a cosmic collision course, set to erupt in a supernova explosion so luminous it could be visible in Earth’s daytime sky within the next century. An international team led by the University of Turku in Finland has confirmed the system’s violently unstable nature, revealing a white dwarf star consuming its partner at an unprecedented rate.
For over a century, the star system V Sagittae has mystified astronomers with its erratic, brilliant flickering. Now, researchers have pieced together its chaotic fate. Located about 10,000 light-years away in the constellation Sagitta, this binary pair isn’t just dancing; it’s spiraling toward a spectacularly violent merger. According to a new study published in Monthly Notices of the Royal Astronomical Society, their death spiral will culminate in a supernova visible to the naked eye, possibly even against the blue canvas of a daytime sky.
So, what makes this star system so special and so doomed? The core of the drama is a white dwarf—the incredibly dense remnant of a sun-like star—that is voraciously pulling material away from its larger companion. Professor Emeritus Phil Charles from the University of Southampton, a co-author of the study, described V Sagittae as a “very important system” shrouded in confusion due to its wildly fluctuating light. The team’s analysis, reported by Live Science, shows the accretion rate is staggeringly high, fueling a continuous thermonuclear reaction on the white dwarf’s surface. This essentially turns it into an “orbiting nuke,” making it the brightest source of its kind in our galaxy.
The data that revealed this dire prognosis came from an intensive 120-day observation period using the X-Shooter spectrograph at the European Southern Observatory’s Very Large Telescope in Chile. By breaking down the star’s light into a spectrum, scientists could probe its composition and dynamics. What they found is a system locked in an ever-tightening embrace, orbiting each other once every 12.3 hours and drawing inexorably closer.
The instability is so extreme that material isn’t cleanly consumed. A significant amount escapes, forming a vast halo of gas called a circumbinary disk that engulfs both stars. This chaotic feeding frenzy causes the system’s brightness to swing dramatically, sometimes shifting in mere days. “From our study we show that no one has yet been able to uniquely identify the orbital motion of each component,” Professor Charles told Live Science via email, highlighting the challenge in pinning down precise stellar masses amidst the turmoil.
Before the final curtain call, skywatchers might be treated to a dazzling preview. Researchers predict the accumulating material could trigger a nova outburst in the coming years or decades. As Professor Pablo Rodríguez-Gil from the Institute of Astrophysics of the Canary Islands, another co-author, stated, this would make V Sagittae easily visible without telescopes. A nova, while explosively bright, is just a surface eruption that leaves the white dwarf intact to continue its feast.
The grand finale, however, is the merger. When the two stars finally coalesce, they will ignite a type Ia supernova. This titanic thermonuclear detonation will, for a fleeting time, outshine entire galaxies. A 2020 study from Louisiana State University projected the collision could happen as soon as 2067, based on the measured speeding up of the orbital period. While stellar evolution timelines are tricky, the direction is clear. “If the period decline continues then it must happen,” noted Professor Charles, while cautioning that the exact date might shift.
Why does this distant cataclysm matter to us? Beyond the sheer celestial spectacle, observing the entire process—from pre-nova to final merger—would provide an unprecedented real-time case study of stellar evolution’s most dramatic chapters. It offers a rare chance to test our models of how binary stars live and die. So, while we mark our calendars tentatively, we can also look up toward the constellation Sagitta, knowing we are witnessing the final, furious act of a stellar drama millennia in the making.
