Blue supergiant star, illustration. This blue supergiant star once existed inside a cluster of young stars in the spiral galaxy NGC 3938, located 65 million light-years from earth. It exploded as a supernova in 2017, and archives of photographs from the NASA/ESA Hubble Space Telescope were used to locate the progenitor star. The star may have been 50 times as massive as the Sun and burned hotter and bluer. When it exploded in 2017, astronomers categorised it as a Type Ic supernova because of the lack of hydrogen and helium in the supernova's spectrum.