Contrary to expectations, the brightest supernova in recorded history left no star in its wake, say astronomers who have searched the celestial wreckage (shown). In 1006, observers watched a star explode in the constellation Lupus that shone about a dozen times more brilliantly than Venus ever does. The explosion was a Type Ia supernova, the most luminous variety, which occurred when a small, dense star known as a white dwarf blew up about 7000 light-years from Earth. Such a supernova is supposed to result when a larger companion star dumps material onto the white dwarf, triggering a runaway nuclear reaction that annihilates the small star. However, as astronomers will report in The Astrophysical Journal, a thorough search for the companion, which should have survived the explosion, has turned up nothing. This finding dovetails with a similar nondetection in a nearby galaxy and suggests the explosion arose instead when two white dwarfs that were in orbit around each other merged and blew up—hinting that more Type Ia supernovae may stem from double white dwarfs than astronomers had thought.
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