2004et was observed at magnitude 15.2 and rose to a maximum visual magnitude of 12.7. Images taken during the preceding days revealed that the supernova explosion occurred on 22 September. The progenitor of the supernova was identified on earlier images –– only the seventh time that such an event was directly identified with its host star. The red supergiant progenitor had an initial mass of about 15 in an interacting binary system shared with a blue supergiant. During 2009, a bright star within NGC 6946 flared up over several months to become over one million times as bright as the Sun. Shortly thereafter it faded rapidly. Observations with the Hubble Space Telescope suggest that the star did not survive, although there remains some infrared emission from its position. This is thought to come from debris falling onto a black hole that formed when the star died. This potential black hole-forming star is designated N6946-BH1. The progenitor is believed to have been a yellow hypergiant star. In May 2017, supernova SN 2017eaw was detected in the northwest region of the galaxy, and light curves obtained over the next 600 days showed that it was a Type II-P. The progenitor was determined to have been a red supergiant, with a mass of around 15. More supernovae have been seen in NGC 6946 than in any other galaxy. See also IC 342 - similar galaxy heavily obscured by Milky Way stars and dust. List of galaxies References External links SEDS: Spiral Galaxy NGC 6946 Atlas of the Universe N6946-BH1 Giant Star Becomes A Black Hole Right Before Our Eyes! Cepheus (constellation) Cygnus (constellation) Intermediate spiral galaxies 6946 11597 65001 029 012b 17980909 Virgo Supercluster