{"paper_id":"23bfb236-4c6d-48fb-be90-aa463ac069fd","body_text":"The dramatic transition of the extreme Red Supergiant WOH G64 to a Yellow Hypergiant | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article The dramatic transition of the extreme Red Supergiant WOH G64 to a Yellow Hypergiant Gonzalo Munoz-Sanchez, Maria Kalitsounaki, Stephan de Wit, Kostantinos Antoniadis, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5551282/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Feb, 2026 Read the published version in Nature Astronomy → Version 1 posted You are reading this latest preprint version Abstract Red Supergiants (RSGs) are cool, evolved massive stars in their final evolutionary stage before exploding as a supernova [1, 2]. However, the evolution and fate of the most luminous RSGs is uncertain. Observational evidence for luminous warm, post-RSG objects [3] and the lack of luminous RSGs as supernova progenitors [4] suggest a blueward evolution. Since the 1980s, WOH G64 has been considered the most extreme RSG in the Large Magellanic Cloud given its outstanding size, luminosity, and mass-loss rate [5–7]. Here we report a sudden, yet smooth change in its nature. Time-series photometry and subsequent spectroscopy revealed the most extreme transition ever seen in the optical spectral features of a RSG. We discovered that WOH G64 is a rare, massive symbiotic system formed by a RSG, which transitioned to a Yellow Hypergiant, and a B-star companion. The dramatic transition can be explained by: a) binary interactions partially stripping the envelope, b) the return of WOH G64 to a quiescent state after an outstanding eruption exceeding 30 years, and c) the expulsion of its outer layers due to a pre-supernova superwind phase, indicating its imminent explosion. WOH G64 offers a unique opportunity to witness stellar evolution in real-time, providing crucial clues for the final phases of massive stars and their resulting supernovae. Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stars WOH G64 massive stars supergiant stars atmospheres late-type stars mass-loss Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Published Journal Publication published 23 Feb, 2026 Read the published version in Nature Astronomy → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-5551282\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Physical Sciences - Article\",\"associatedPublications\":[],\"authors\":[{\"id\":389523878,\"identity\":\"f55fe97e-2c78-4716-a9e0-4427a9560f2d\",\"order_by\":0,\"name\":\"Gonzalo 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