One of the largest known stars in the universe has undergone a dramatic transformation that astronomers believe could signal the beginning of its final act. WOH G64, a colossal star located about 163,000 light-years away in the Large Magellanic Cloud, has shifted from a red supergiant into a rare yellow hypergiant, a change that may precede a supernova explosion.
The findings, reported after years of observation, suggest the 1,540-solar-radius star has rapidly increased in temperature and changed color in a smooth transition rarely witnessed in real time, according to Space.com. With nearly 30 times the mass of the sun and more than 280,000 times its brightness, WOH G64 ranks among the most extreme stellar objects known.
First identified in the 1970s, the star was long classified as a red supergiant surrounded by a thick torus of dust. But in 2014, astronomers led by Gonzalo Muñoz-Sanchez of the National Observatory of Athens detected a clear shift in its spectrum, indicating a rise in surface temperature consistent with evolution into a yellow hypergiant. Such objects represent a brief transitional phase between red supergiants and their eventual fate, which may involve a supernova explosion or direct collapse into a black hole.
Massive stars burn through nuclear fuel at extraordinary rates, meaning they live only a few million years. At just 5 million years old, WOH G64 is already nearing the end of its life. Yet its exact fate remains uncertain. Stars in the 23 to 30 solar mass range occupy a gray zone in stellar evolution models, with some exploding as supernovas and others collapsing directly into black holes without a visible blast.
Complicating matters further, researchers discovered that WOH G64 is part of a binary system. Interactions with a companion star may have stripped away part of its outer envelope, accelerating its transformation. Alternatively, the changes may be driven by internal stellar processes alone.
Astronomers estimate that if core collapse does occur, it could happen within a few hundred to a few thousand years, an instant in cosmic terms but unlikely within a human lifetime. Whether WOH G64 ultimately explodes or quietly collapses into a black hole, its ongoing evolution offers a rare window into the final stages of the universe’s most massive stars.
The study has been published here.