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One of the biggest stars in the universe might be ready to explode
earthsky.org
One of the largest known stars in the universe, WOH G64, is changing rapidly. New research shows this stellar giant may be getting ready for its final, explosive end in a supernova. A study published in the journal Nature Astronomy in 2024 provides evidence that WOH G64 has changed from a red supergiant into a rare yellow hypergiant. Astronomers first noticed this dramatic shift in 2014. The research, led by Gonzalo Muñoz-Sanchez of the National Observatory of Athens, suggests the star is losing its outer layers, becoming smaller, and heating up as it nears the end of its relatively short life. This process might be a sign that a supernova, one of the universe's most powerful explosions, is coming.
WOH G64 is located in the Large Magellanic Cloud, a small galaxy that orbits our Milky Way. It was first identified in the 1970s as an object of great interest. Later observations showed it is not only incredibly bright but also one of the most physically huge stars ever found. Its radius is more than 1,500 times that of our sun. In 2024, astronomers made a breakthrough by capturing the first detailed image of a star outside our galaxy, using the Very Large Telescope Interferometer. This image clearly showed a vast, dusty cloud surrounding the central star, confirming that it was losing mass—a key sign a star is aging.
In cosmic terms, WOH G64 is very young, with an estimated age of less than 5 million years. This is very different from our middle-aged sun, which is about 4.6 billion years old. Massive stars like WOH G64 are destined to "live fast and die young." They form from the collapse of huge clouds of gas and dust, igniting under intense pressure. At first, they fuse hydrogen into helium in their cores, much like our sun. As they use up this fuel, they expand and begin fusing helium, entering the red supergiant phase.
Not all supergiants become hypergiants. Theoretical models suggest hypergiants form when exceptionally massive stars burn through their nuclear fuel very quickly, rapidly changing from hydrogen to helium fusion. During this critical phase, the star throws off its outer layers while its core shrinks. Once a star becomes a hypergiant, its fate is sealed: a fast progression toward a supernova explosion is certain.
The major change seen in WOH G64 in 2014 raises an important question: what caused it? The new study proposes one explanation: a large part of the star's outer surface may have been violently blown off. This event could have been started by gravitational interactions with a companion star, which the researchers confirmed exists by analyzing the star's light spectrum.
Another theory, which could also be true, is that the star is entering a final preparatory stage before exploding. While it is certain that a star this big will eventually end its life in a supernova, predicting the exact timing is extremely hard. The observed transition may be driven by a powerful pre-supernova "superwind." This theoretical phase is thought to happen because of intense internal shaking as the star's core rapidly uses up its last nuclear fuel.
Most stars exist for millions or even billions of years, making big changes over a human lifetime almost impossible to see. Therefore, the chance to witness and record such a fast transformation in a star—especially one in another galaxy—is extraordinary. If astronomers are lucky, the final supernova of WOH G64 may happen within our lifetimes. Such an event would not only provide a breathtaking intergalactic show but would also give invaluable data, allowing scientists to complete their understanding of this fascinating stellar lifecycle.
By Sara Webb, Lecturer, Centre for Astrophysics and Supercomputing, Swinburne University of Technology
This article is republished from The Conversation under a Creative Commons license.
Summary: One of the universe's largest stars, WOH G64, is showing signs of a dramatic transformation observed since 2014, suggesting it may be nearing a supernova explosion. Research indicates it has changed from a red supergiant to a yellow hypergiant, losing mass and heating up as it approaches the end of its short, intense life.