A team describes the star that originated the nearby supernova SN 2025pht
A recent analysis succeeds in defining the properties of the progenitor star that caused the supernova SN 2025pht, a bright stellar event in the galaxy NGC 1637. This work leverages unique observations captured just before the star exploded, combining data from the Hubble Space Telescope and the James Webb Space Telescope. 🪐
A unique snapshot before the cataclysm
Astronomers obtained what can be considered a quasi-snapshot of the star's nature in its final moments. Hubble first detected it in 2001, but it was James Webb that, in 2024, observed it in a dozen spectral bands shortly before its explosion. The star showed changes in its brightness, indicating it may have been a pulsating variable with a long cycle of about 660 days.
Main findings of the study:- The candidate was an extremely cold red supergiant, with a temperature between 2100 and 2500 Kelvin.
- Its bolometric luminosity is estimated at log(L_bol/L_Sun)=5.08, with an error margin of +/- 0.16.
- The medium surrounding the star was very rich in silicate dust, as revealed by modeling how radiation is transferred.
For the first time, without the JWST archive observations, this progenitor candidate could not have been detected or characterized at all.
The challenges in precisely determining the data
The biggest obstacle to accurately defining the stellar parameters was the distance to the host galaxy. The team calculates that NGC 1637 is at 10.73 megaparsecs, with an uncertainty of +/- 1.76 Mpc. Additionally, the interstellar dust within the galaxy itself significantly obscured the star, causing a visual attenuation of approximately 1.7 magnitudes.
Factors that complicated the analysis:- The uncertainty in distance directly affects the calculation of luminosity and the star's real size.
- Dust extinction from galactic and circumstellar dust masked its true brightness and color.
- Hubble's optical data alone did not allow defining the full shape of its spectral energy distribution.
The crucial role of the James Webb telescope
The infrared capabilities of the JWST were decisive. They penetrated the dense mantle of dust that hid the red giant, allowing its detection and characterization. Although this progenitor resembles that of the supernova SN 2023ixf, the one for SN 2025pht could be the most luminous candidate identified to date. This case demonstrates that cosmic dust is not just a hindrance; it can completely hide a massive star about to explode, until an instrument powerful enough arrives to see through it. 🔭