Supergiant Star Makes Rare Leap to Hotter Phase, Astronomers Say

Long-term observations of WOH G64 – once thought to be the most extreme red supergiant star in its galaxy – reveal that the star underwent a dramatic transition, possibly losing some of its outer layers as it entered a hotter, rarer stellar phase.

Artistic reconstruction of the red supergiant WOH G64. Image credit: ESO / L. Calçada.

Red supergiants are stars with a mass more than 8 times that of the Sun and have a relatively short lifespan, of only 1 to 10 million years, before exploding into supernovae.

However, the evolution and fate of the most luminous red supergiants remains uncertain.

Since its discovery in the 1980s, WOH G64 has been considered one of the brightest, largest and coolest red supergiants in the Large Magellanic Cloud, a dwarf galaxy located about 160,000 light-years from our solar system.

To study the evolution of WOH G64, Dr. Gonzalo Muñoz-Sanchez of the Athens National Observatory and colleagues examined more than 30 years of brightness measurements from 1992, combining them with new archived electromagnetic spectra.

They found that the star underwent rapid changes, initially fading in 2011 before recovering and becoming yellower and hotter – by more than 1,000 degrees Celsius – in 2013-2014.

By 2025, WOH G64 has faded significantly and experienced changes in its atmospheric chemistry.

This image, taken by the GRAVITY instrument on ESO’s Very Large Telescope Interferometer, shows the red supergiant WOH G64. Image credit: ESO / Ohnaka and others., doi: 10.1051/0004-6361/202451820.

To explain these developments, astronomers suggest two potential scenarios.

“First, WOH G64 could be part of a binary star system in which the red supergiant transitioned to a yellow hypergiant due to an interaction that triggered the ejection of part of its atmosphere,” they said.

“In an alternative scenario, a yellow hypergiant could have experienced an eruption of material that made it appear red for several decades, ending in 2014.”

“The results raise the question of whether extreme red supergiants, such as WHO G64, exist because they are interacting binaries and therefore would not reach these extreme states if they were single stars,” they added.

“Future interactions will determine whether this star explodes as a supernova, collapses into a black hole, or merges with its companion.”

The study was published in the journal Natural astronomy.

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G. Muñoz-Sanchez and others. The dramatic transition from the extreme red supergiant WOH G64 to a yellow hypergiant. Nat Astronpublished online February 23, 2026; doi: 10.1038/s41550-026-02789-7