'Supernova Impostor' Star Hides a Compact Companion, Not an Explosion

For a decade, a star named AT 2016blu — about 29 million light-years away and roughly 33 times as massive as the sun — has teased astronomers with signs that it might be about to explode as a supernova. New research shows something else is behind its behavior: a previously unseen companion.

The star is a luminous blue variable, a type of extremely massive, unstable star, discovered in 2012. Since then it has erupted 27 times in outbursts that looked very supernova-like, earning it the nickname "supernova impostor." Papers in 2023 and 2025 suggested a binary system, not an imminent explosion, was responsible, but left key questions unanswered.

Because the outbursts recur roughly every 113 days, lead author Mojgan Aghakhanloo of the University of Virginia and colleagues could predict the next one and arrange observations in advance, drawing on multiple telescopes and more than 30 amateur astronomers. During the predicted peak outburst in March 2026, the team triggered a "Target of Opportunity" request that pulled NASA's Chandra X-ray Observatory off its schedule to watch. Chandra detected an X-ray source during the outburst — but earlier, incidental Chandra observations from 2001-02, when the star was quiet, had shown no X-rays at all.

X-rays are produced when a star pulls in and gathers material from a companion — a process called accretion — heating it until it radiates; the luminosity Chandra measured matched the accretion rate expected from a compact companion such as a black hole or neutron star. The findings make the star the first known case of a luminous blue variable whose outbursts are driven by intermittent accretion onto a compact object, forming what astronomers call a high-mass X-ray binary, with the living star slowly losing mass to its dead companion as they orbit. The research appears in The Astrophysical Journal.

The star is not the only supernova impostor; Aghakhanloo has secured more time on Chandra to study others, and the Vera Rubin Observatory's upcoming 10-year sky survey is expected to uncover many more such systems.