An Exceptional Dimming Event for a Massive, Cool Supergiant in M51

Understand

We present the discovery of an exceptional dimming event in a cool supergiant star in the Local Volume spiral M51.

• The star, dubbed M51-DS1, was found as part of a Hubble Space Telescope (HST) search for failed supernovae (SNe).
• The supergiant, which is plausibly associated with a very young ($\lesssim6$ Myr) stellar population, showed clear variability (amplitude $\Delta F814W\approx0.7$ mag) in numerous HST images obtained between 1995 and 2016, before suddenly dimming by $>$2 mag in $F814W$ sometime between late 2017 and mid-2019.
• In follow-up data from 2021, the star rebrightened, ruling out a failed supernova.