`Post-mortem` gives insight into Kepler`s supernova
Washington: An analysis of X-ray observations from the Japan-led Suzaku satellite has concluded that an exploding star observed in 1604 by the German astronomer Johannes Kepler held a greater fraction of heavy elements than the sun.
The findings will help astronomers better understand the diversity of type Ia supernovae, an important class of stellar explosion used in probing the distant universe.
"The composition of the star, its environment, and the mechanism of the explosion may vary considerably among type Ia supernovae," said Sangwook Park, an assistant professor of physics at the University of Texas at Arlington.
"By better understanding them, we can fine-tune our knowledge of the universe beyond our galaxy and improve cosmological models that depend on those measurements," Park added.
The best way to explore the star`s makeup is to perform a kind of post-mortem examination on the shell of hot, rapidly expanding gas produced by the explosion. By identifying specific chemical signatures in the supernova remnant, astronomers can obtain a clearer picture of the composition of the star before it blew up.
"Kepler`s supernova is one of the most recent type Ia explosions known in our galaxy, so it represents an essential link to improving our knowledge of these events," said Carles Badenes, an assistant professor of physics and astronomy at the University of Pittsburgh.
Using the Suzaku satellite`s X-ray Imaging Spectrometer (XIS), the astronomers observed the remnant of Kepler`s supernova in 2009 and 2011. With a total effective XIS exposure of more than two weeks, the X-ray spectrum reveals several faint emission features from highly ionized chromium, manganese and nickel in addition to a bright emission line from iron. The detection of all four elements was crucial for understanding the original star.
Cosmologists regard type Ia supernovae as "standard candles" because they release similar amounts of energy. By comparing this standard to the observed peak brightness of a type Ia supernova, astronomers can pin down its distance. Their similarity stems from the fact that the exploding star is always a compact stellar remnant known as a white dwarf.
The findings provide strong evidence that the original white dwarf possessed roughly three times the amount of metals found in the sun. Progressive stellar generations seed interstellar gas with increasing proportions of metals.
The remnant, which lies about 23,000 light-years away toward the constellation Ophiuchus, lies much closer to our galaxy`s crowded central region than the sun does. There, star formation was probably more rapid and efficient. As a result, the star that blazed forth as Kepler`s supernova likely formed out of material that already was enriched with a higher fraction of metals.
While the Suzaku results do not directly address which type of binary system triggered the supernova, they indicate that the white dwarf was probably no more than a billion years old when it exploded, or less than a quarter of the sun`s current age.
The researchers discuss the findings in a paper scheduled for publication in the April 10 issue of The Astrophysical Journal Letters and now available online.
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