An exceptionally large celestial body within our Universe has exhibited an anomalous phenomenon, prompting scientific discourse regarding its implications.
WOH G64, an immense star situated in the Large Magellanic Cloud, is — or perhaps was — recognized as one of the preeminent red supergiants, boasting a diameter exceeding 1,500 times that of our Sun. Observations conducted by telescopes in 2013 and 2014 documented a striking metamorphosis, wherein the star appeared to transition from its characteristic red supergiant state to a hotter, more yellowish configuration.
A cohort of researchers spearheaded by Gonzalo Muñoz-Sanchez of the National Observatory of Athens in Greece posited that the star had entered a rare yellow hypergiant phase, signaling a potential precursor to its ultimate dissipation.
In their study, disseminated via the preprint repository arXiv in November 2024, they contended that this alteration signified an abrupt shift from a red supergiant to a transient evolutionary epoch that may precede a core-collapse supernova.
“This profound alteration,” the researchers articulate in their subsequently published findings, “can be attributed either to the partial expulsion of its pseudo-atmosphere during a common-envelope event or a return to a stable state following an extraordinary outburst lasting over three decades.”
Their analytical assessment indicated a concomitant rise in temperature, a reduction in dimensions to approximately 800 solar radii, and modifications in its atmospheric composition. Furthermore, they detected the presence of a luminous binary companion star engaged in an interaction with its more expansive, enveloping counterpart.
However, more recent observational data suggest that the star may not have deviated from its red supergiant classification at any point.
Red supergiants constitute some of the most volumetrically significant stars in the cosmos, arising from massive stellar progenitors typically spanning 8 to 30 solar masses, which are in the terminal phases of their nuclear fusion cycles. As a red supergiant exhausts its primary nuclear fuel and transitions to heavier elements, it undergoes significant expansion, with its outer envelope extending to hundreds of times the solar radius.
Such stellar entities are inherently unstable and prone to dramatic transformations, including fluctuations in luminosity or color, as they eject material into the interstellar medium.
Positioned approximately 160,000 light-years distant, WOH G64 is remarkable for both its immense size and the extensive observational scrutiny it has received, affording astronomers a valuable opportunity to study the behavior of colossal stars in their final evolutionary stages.
Nevertheless, the interpretation of the dynamics of these inherently volatile stars presents considerable challenges. A variation in brightness or spectral hue does not invariably signify a fundamental alteration in the star’s identity.
Between November 2024 and December 2025, astronomers Jacco van Loon of Keele University in the United Kingdom and Keiichi Ohnaka of Universidad Andrés Bello in Chile undertook observational campaigns utilizing the Southern African Large Telescope.
In January 2026, their findings were published in the esteemed journal *Monthly Notices of the Royal Astronomical Society*. Their analysis revealed the presence of titanium oxide within WOH G64’s atmosphere.
Conversely, a yellow hypergiant is of a temperature too elevated to sustain the existence of titanium oxide.
“It has been asserted that WOH G64 transformed into a yellow hypergiant, a phenomenon that could indicate an evolutionary trajectory preceding a supernova event following its red supergiant phase,” van Loon commented.
“Nevertheless, our recent spectral data acquired with SALT confirm the existence of the hot companion while also exhibiting distinct molecular absorption bands indicative of titanium oxide. This suggests that WOH G64 currently remains a red supergiant and may never have transitioned away from this state.”
The occurrence of a red supergiant star exhibiting peculiar changes that do not necessarily presage an imminent stellar explosion is not unprecedented; indeed, one might recall the dramatic variability observed in Betelgeuse, during which its luminosity diminished by nearly 25 percent.
This does not negate the possibility that extraordinary events are unfolding within the star. Van Loon and Ohnaka concur that the star likely possesses a binary companion. They theorize that interactions between these two stellar bodies may have perturbed their immediate surroundings, generating alterations that could mimic a spectral shift without necessitating a fundamental evolutionary leap.
To achieve a more comprehensive understanding of the phenomena occurring with WOH G64, ongoing monitoring is imperative. Its continued evolutionary progression will furnish scientists with a clearer perspective on whether the star is poised at the precipice of an evolutionary transition or if such variability represents its current normative state.
One certainty, however, remains unequivocally apparent: this enigmatic stellar system is replete with surprises and will undoubtedly persist as a captivating celestial entity.
The scholarly work presented by Gonzalo Muñoz-Sanchez and his research group has been formally published in the journal *Nature Astronomy*.
