The apparently peaceful spiral galaxy pictured above in the constellation Eridanus -- the River -- has hosted two violent supernovae in the last 30 years, belying its tranquillity, astronomers said.
Called NGC 1187, the galaxy lies about 60 million light-years from Earth and was discovered by English astronomer William Herschel in 1784. It was notable mostly for lying face-on to the Earth, which provides an excellent view of its spiral arms. The bluish features of the arms indicate the presence of young stars born out of interstellar gas, while the yellow bulge at the center is mostly made up of old stars, gas and dust.
In October 1982, astronomers at the European Southern Observatory's La Silla Observatory in Paranal, Chile, observed a supernova in the galaxy. In 2007, amateur astronomer Berto Monard of South Africa observed a second one, which was observed with multiple telescopes for more than a year.
Supernovae can occur at the end of a massive star's lifetime when its nuclear fuel is exhausted and gravity causes it to collapse on itself, producing a violent explosion that outshines a galaxy. Alternatively, they can also occur in a binary star system when a carbon-oxygen white dwarf pulls so much matter from a higher-mass companion star that the larger star collapses on itself. Remnants of the 2007 supernova are still visible as a small red dot at the bottom center of the image.