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WOH G64, one of the largest stars ever identified, underwent a dramatic change in 2014, was documented in detail in 2024, and is now viewed by astronomers as a rare yellow hypergiant that may be entering the final phase before a supernova.
The star WOH G64, one of the largest known in the Universe, underwent a dramatic transformation in 2014 and is now pointed out by astronomers as a possible candidate to explode. The new study indicates that it has transitioned from a red supergiant to a rare yellow hypergiant, in a process that may precede a supernova.
The research was led by Gonzalo Muñoz-Sanchez from the National Observatory of Athens and published in the journal Nature Astronomy. The gathered evidence suggests that the star may be shedding its outer layers, shrinking as it heats up and advancing toward the final stage of its short existence.
One of the largest stars ever found
WOH G64 was first identified in the 1970s as an object of interest in the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way. Later, astronomers found that it was not only extremely bright but also one of the largest stars ever discovered.
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Its size is impressive: the star has more than 1,500 times the radius of the Sun. Even though it is young on a cosmic scale, at less than 5 million years old, WOH G64 is already following a very different trajectory from that of the Sun, which is currently about 4.6 billion years old.
The star formed from a massive cloud of gas and dust that collapsed until the pressure triggered its ignition. In its evolution, it would have burned hydrogen in the core through nuclear fusion and later expanded and started burning helium, becoming a red supergiant.
Recorded change and mass loss
In 2024, WOH G64 became the first star outside our galaxy to be photographed in detail. The record was obtained with the Very Large Telescope Interferometer and revealed a well-defined dust cocoon around the giant central star.
The image reinforced that it has been losing mass over time. This behavior gained even more relevance with the new study, which supports that the star transitioned from a red supergiant to a yellow hypergiant after a transformation observed in 2014.
Not every supergiant becomes a hypergiant. One of the existing hypotheses is that this rare type of star arises when very large stars burn quickly and advance from burning hydrogen to helium, also starting to lose its outer layers as the core begins to contract.
What may have happened in 2014
The new study proposes that, in 2014, a large part of the original surface of the supergiant was ejected away from WOH G64. This process may have been triggered by interactions with a companion star, whose existence was confirmed by the authors when analyzing the light spectrum of the star.
There is also another possibility considered by the researchers. The observed transition may be linked to a phase of “superwind” pre-supernova, caused by strong internal pulsations as the core fuel rapidly depletes.
When a star reaches the hypergiant stage, it is associated with a rapid death in a supernova explosion. Scientists know that stars of this size will inevitably explode, but it is still difficult to define exactly when this will happen.
A rare process observed in real time
Most stars live for tens of millions or even tens of billions of years. Therefore, recording so many changes in a star, especially one that is outside our galaxy, was not something guaranteed.
If the evolution of WOH G64 continues as astronomers suspect, it could provide a rare real-time follow-up of the final moments of a massive star. The eventual explosion could also help scientists better understand the mechanisms surrounding the transformation and death of this star.
With information from TC.
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