This nova was spotted in March 2021, the star V1405 Cassiopeia suddenly showed a dramatic increased in brightness.

A nova is an astronomical event that causes a dramatic increase in brightness of a star, this is not to be confused with a supernova (an exploding star).

All observed novae always occur in a binary (2 star) system. With one star being a white dwarf and either a main sequence star (like our sun), a subgiant or a red giant star. When the white dwarf is close enough in its orbit to its companion star, it starts drawing matter onto its own surface. This matter is mainly hydrogen which is heated by the hot white dwarf and eventually reaches a critical temperature which causes ignition of rapid runaway fusion.

This sudden increase in energy expels the hydrogen into interstellar space seen as visible light which causes the enormous increase in brightness for some time.

The animated gif shows this dramatic increase clealy as one image was taken in september 2012. Please note that the image of the nova was taken through a hydrogen alpha filter, which shows smaller starsizes compared to traditional RGB.