New findings from NASA's Chandra X-ray Observatory have provided a major advance in understanding a type of supernova critical for studying the dark energy that astronomers think pervades the universe. The results show that mergers of two dense stellar remnants are the likely cause of many of the supernovae that astronomers have used to measure the accelerated expansion of the universe.
These supernovae, called type Ia, serve as cosmic mile markers to measure expansion of the universe because they can be seen at large distances and they follow a reliable pattern of brightness. However, until now, scientists have been unsure what actually causes the explosions.
"Our results suggest the supernovae in the galaxies we studied almost all come from two white dwarfs merging," said Akos Bogdan, also of Max Planck. "This is probably not what many astronomers would expect."
The difference between these two scenarios may have implications for how scientists can use these supernovae as "standard candles" — objects of a known brightness — to track vast cosmic distances. Because white dwarfs can come in a range of masses, the merger of two could result in explosions that vary somewhat in brightness.
Because these two scenarios would generate different amounts of X-ray emission, Gilfanov and Bogdan used Chandra to observe five nearby elliptical galaxies and the central region of the Andromeda Galaxy. A type Ia supernova caused by accreting material produces significant X-ray emission prior to the explosion. A supernova from a merger of two white dwarfs, on the other hand, would create significantly less X-ray emission than the accretion scenario.
The scientists found the observed X-ray emission was a factor of 30 to 50 times smaller than expected from the accretion scenario, effectively ruling it out. This implies that white dwarf mergers dominate in these galaxies.
The difference between these two scenarios may have implications for how scientists can use these supernovae as "standard candles" — objects of a known brightness — to track vast cosmic distances. Because white dwarfs can come in a range of masses, the merger of two could result in explosions that vary somewhat in brightness.
Because these two scenarios would generate different amounts of X-ray emission, Gilfanov and Bogdan used Chandra to observe five nearby elliptical galaxies and the central region of the Andromeda Galaxy. A type Ia supernova caused by accreting material produces significant X-ray emission prior to the explosion. A supernova from a merger of two white dwarfs, on the other hand, would create significantly less X-ray emission than the accretion scenario.
The scientists found the observed X-ray emission was a factor of 30 to 50 times smaller than expected from the accretion scenario, effectively ruling it out. This implies that white dwarf mergers dominate in these galaxies.
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