No signature of ejecta interaction with a stellar companion in three type Ia supernovae

The explosion of a type Ia supernova could be triggered either by accretion from a companion—which should be indicated by brightening caused by interaction of supernova ejecta with the companion—or by a merger with a white dwarf or other small star; here observations by the Kepler mission of three type Ia supernovae reveal no such brightening, leading to the conclusion that they were triggered by a merger.