WASHINGTON, June 27 (UPI) -- The National Aeronautics and Space Administration's Swift satellite has discovered two supernovas during the past six weeks in the constellation Hercules.
NASA said the sightings mark the first time astronomers have observed two such powerful stellar explosions occurring in the same galaxy so close together in time.
The galaxy is 380 million light-years from Earth and, until this year, astronomers had never sighted a supernova in that area.
A supernova is an extremely energetic and life-ending explosion of a star.
Making the event even more unusual is the fact the two supernovas belong to different types. Supernova 2007ck is a Type II event triggered when the core of a massive star runs out of nuclear fuel and collapses. It was first observed May 19.
Supernova 2007co is a Type Ia event, which occurs when a white dwarf star accretes so much material from a binary companion star that it explodes. It was discovered June 4.
"Most galaxies have a supernova every 25 to 100 years, so it's remarkable to have a galaxy with two supernovae discovered just 16 days apart," said Stefan Immler of NASA's Goddard Space Flight Center.
