NGC 6946 (also known as the Fireworks Galaxy, Arp 29, and Caldwell 12) is a medium-sized, face-on spiral galaxy about 22.5 million light years away from Earth located in the constellations Cepheus and Cygnus. At about 20,000 light years wide, it’s one of about a dozen nearby neighbors to the Milky Way. Since its discovery by William Herschel on September 9, 1798, nine supernovas (death explosions of massive stars) have been observed to explode in the arms of this unusually active galaxy. Chandra observations (purple) have, in fact, revealed three of the oldest supernovas ever detected in X-rays, giving more credence to its nickname of the “Fireworks Galaxy.”
By contrast, the average rate of supernovas in our galaxy is about one every 100 years. Obviously, the Fireworks Galaxy is undergoing a tremendous burst of star formation with no obvious cause. The composite image agove also includes optical data from the Gemini Observatory in red, yellow, and cyan.
For those trying to find it in their scopes, it’s located at right ascension 20h 34m 52.3s, declination +60° 09′ 14″ (bright in infrared light but highly obscured by interstellar matter as it is quite close to the galactic plane). In the photo below, the galaxy’s colors change from the yellowish light of old stars in the core to young blue star clusters and reddish star forming regions along the loose, fragmented spiral arms.
The nine supernovas thus far include SN 1917A, SN 1939C, SN 1948B, SN 1968D, SN 1969P, SN 1980K, SN 2002hh, SN 2004et, and SN 2008S.