A supernova is a powerful and bright explosion of a star. A supernova typically occurs in the last stages of the evolution of a massive star (much bigger than our Sun) or when nuclear fusion is suddenly re-triggered in a dwarf star. A supernova explosion produces an incredible amount of energy and mass, expelling several solar masses and producing about the same amount of energy produced by our Sun during its entire 8-10 billion-year expected lifespan. But with supernovae, all this occurs just in a few days or weeks.
Several supernovae are observed in galaxies yearly, but that's because thousands of galaxies are constantly monitored. A supernova is a relatively rare event for any given galaxy. Supernovae have also been observed in our Milly Way, but the last reported such event was in 1604 (SN1604, described by Johannes Kepler).
On 19 May 2023 a supernova (dubbed SN2023ixf) went off in Messier 101 (M101), a well-known galaxy located in constellation Ursa Major (aka the "Big Dipper") about 20 million light-years away. Shining at mag 15 at the time of discovery by Koichi Itagaki, by the time I imaged it on 26 May, its brightness had gone up to mag. 11. This is a 40-fold brightness increase in barely a week.
My image below was acquired through a 10-inch TS RC @f/5.5 with a QHY163M camera. RGB only, 7 x 5 min = 35 min. for each channel. Let's see how it evolves, in the meantime, enjoy!