This type II (core collapse) supernova was discovered by amateur astronomer Koichi Itagaki on 2023 May 19. Subsequent searches of survey images found captures from two days earlier. The supernova is in the Pinwheel Galaxy, M101, only 21 million light years away (next door in astronomical terms). It brightened over the first few days, and will likely remain visible for a few months. Supernovas like this begin with a massive star (at least eight times the mass of the Sun) that runs out of fuel, and cannot support itself against its own massive gravity. In seconds it collapses into its core, releasing a massive amount of material and energy, and leaving behind either a neutron star or a black hole.
Imaged on 2023 May 23. Luminance stack of 128 60-second images combined with color data from 2021. Even with 60-second subs, the supernova saturated the sensor. 10-second test exposures did not, and allowed me to determine that the supernova was about 20 times brighter than the galactic core.
Animation. Before and after images from 2021 June 8 (no supernova) and 2023 May 23 (supernova).
Finder. The Pinwheel Galaxy is located near the end of the handle of the Big Dipper.
Supernova coordinates. Annotated version of the image above.