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Type Ia supernovae (SNe Ia) have been used as standardizable candles to discover the accelerating expansion of the universe, leading to the revelation of dark energy and the award of 2011 Nobel Prize in Physics to astronomers. Important as they are, SNe Ia are not fully understood. It is not clear whether they originate from (1) white dwarfs accreting from binary companion stars or (2) mergers of two white dwarfs. To probe the nature of SNe Ia, we search for clues to their previous life in the remains of explosions, called supernova (SN) remnants: if a surviving companion or a dense circumstellar medium from companion’s mass loss is detected, the origin of accreting white dwarf can be affirmed. Over the past decades, no surviving companion has been unambiguously confirmed in the Milky Way. We thus decided to push the boundary to other galaxies. Using images and spectra of stars, we identified possible surviving companions outside the Milky Way for the first time. We reported the first detection of dense circumstellar medium within three extragalactic SN Ia remnants. These studies indicate that the origin of accreting white dwarf for SNe Ia could be more prevalent than people previously thought.