The Progenitor of the Type II-Plateau SN 2025pht in NGC 1637: The Dustiest, Most Luminous Red Supergiant So Far?

We provide a characterization of the red supergiant (RSG) progenitor candidate for the nearby Type II-plateau supernova (SN) 2025pht in NGC 1637. The star was first detectable in 2001 by the Hubble Space Telescope (HST) and then again in a dozen bands by the James Webb Space Telescope (JWST) in 2024. This “quasi-snapshot” of the star’s nature almost immediately prior to explosion is unprecedented. The RSG varied in brightness, and we posit that it could have been a pulsating variable, possibly with a long period of ∼660 days. The largest uncertainty is the host-galaxy distance, which we establish to be 11.67 ± 0.27 Mpc. The star was also heavily extinguished by interstellar dust internal to the host, with visual extinction A V (host) ≈ 1.7 mag (total A V (tot) ≈ 1.8 mag). Dust radiative-transfer modeling reveals the star’s circumstellar medium to be quite dusty and silicate-rich, yielding a bolometric luminosity as high as log ( L bol / L ⊙ ) = 5.16 ± 0.03 and a cool effective temperature T eff = 2100–2500 K. The available HST optical data had no bearing on the shape of the candidate’s observed spectral energy distribution—for the first time, without the archival JWST observations, we would not have been able to detect and characterize the candidate at all. The SN 2025pht progenitor candidate, although similar to that of SN 2023ixf, may be the most luminous star identified to date.