Astronomers watched as the star WOH G64 transformed from a red supergiant into a rare, shortlived yellow supergiant star...in just 12 years.
It's a dramatic, rapid instability in a star that is rapidly headed toward a cataclysmic supernova explosion.
https://theconversation.com/one-of-the-biggest-stars-in-the-universe-might-be-getting-ready-to-explode-276519 #space #science #nature
WOH G64 is an enormous star, 2000 times the diameter of the Sun. If you put it in the Solar System, it would extend out to the orbit of Saturn!
It's so big that we can take a direct picture of it, even though it lies outside our own galaxy. The illustration offers a closer look at what's going on here.
https://www.eso.org/public/news/eso2417/ #science #nature #astronomy
Something dramatic happened to the star WOH G64 around 2014: maybe an interaction with a companion star, or the clearing of an enormous eruption.
The lines show how the star's spectrum completely changed between 2007 & 2016. We've never seen anything quite like this.
That, or somebody just cracked it open!
@coreyspowell There was a counterargument "no, it's still a red giant" paper published to arxiv back in January. I've not got the knowledge or education to have an opinion who might be right:
For a long time, WOH G64 was known as the most extreme red supergiant outside our Galaxy. However, in a matter of years it has faded, its pulsations have become suppressed and the spectrum has become dominated by emission lines from ionised gas, a far cry from the Mira-like pulsation and late M-type spectrum it used to display. Around the same time, a hot dust cloud was discovered using the VLT interferometer. WOH G64 has been claimed to have turned into a yellow hypergiant, which could signal a pre-supernova post-red supergiant evolution. Here we present spectra of WOH G64 obtained with the Southern African Large Telescope (SALT) between November 2024 and December 2025. Molecular absorption bands from TiO are seen at all times. This implies that WOH G64 is currently a red supergiant, and may never have ceased to be. However, the shallow, resolved bands and possible detection of VO hint at a highly extended atmosphere. The continuum appears to be varying, while the line emission shows a different behaviour, suggesting two separate components in the system. Meanwhile, atomic absorption lines are deepening. This places important constraints on scenarios for the dramatic events that are unfolding.
Corey S Powell
David Hopeward
Ross of Ottawa
Paul Drye