WOH G64 A

A red supergiant star located 160,000 light years away in the Large Magellanic Cloud, it is the largest known star with a precisely measured radius, at 1,540 times that of the sun, which makes it the 2nd largest star after V538 Carinae, Photometric measurements spanning from 30 years showed a transition from semi-regular to irregular variability during around 2014, which together with the absence or strength of certain spectral lines in spectroscopic observations that would be inconsistent with a red supergiant, led to Munoz-Sanchez et al. (2024) to conclude that WOH G64 A transitioned from a red supergiant to a yellow hypergiant. The lack of a violent outburst and smooth transition would be explained by the presence of a B-type companion forming a symbiotic binary. As a yellow hypergiant, WOH G64 A would be half of its original size, at 800 R☉, and have a hotter effective temperature of 4,700 K with a likely spectral class of either early K or late G.

This interpretation was subsequently challenged by van Loon & Ohnaka (2026), which detected molecular absorption bands of titanium oxide in spectroscopic data taken between 2024 and 2025, implying that the central component is still a red supergiant. The anomalies observed by Munoz-Sanchez et al. (2024) were explained instead by the periastron passage of the companion: Its tidal forces stretched the outer layers of the primary's atmosphere, causing the atmospheric layer of optical depth 1 to be an inner layer that has a hotter temperature, instead of a cooler layer as it used to be. This, in turn, changes the nature of the variability. Since then, the star has returned to its original state.