Kepler's Supernova Contains Higher Heavy Metal Content Than Our Sun
April 9, 2013

Kepler’s Supernova Contains Higher Heavy Metal Content Than Our Sun

Brett Smith for - Your Universe Online

Using observations made from the Suzaku satellite, a joint venture between Japan's space agency and NASA, an international team of researchers has found that the star responsible for Johannes Kepler´s famous supernova contained a much higher heavy metal content that our own sun.

After determining the makeup of the distant star, the scientists said they have a greater understanding of Ia supernovae, a useful class of stellar explosion for learning about the distant universe, according to the team´s report in The Astrophysical Journal Letters.

"The composition of the star, its environment, and the mechanism of the explosion may vary considerably among type Ia supernovae," said co-author Sangwook Park, a physics professor at the University of Texas at Arlington (UTA). "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."

In 1604, the German astronomer Johannes Kepler first observed what he believed was a new star, but was actually the supernova of a white dwarf star about 20,000 light years away.

Using X-ray imaging from the Suzaku satellite, the scientists were able to identify specific chemical signatures in the remaining shell of hot, expanding gas. An analysis of the images revealed several faint emission features from metals such as chromium, manganese, nickel and iron. The analysis also suggested that the supernova´s original white dwarf contained about three times the amount of metals found in our sun.

"Suzaku's XIS instrument is uniquely suited to this type of study thanks to its excellent energy resolution, high sensitivity and low background noise," co-author Koji Mori, an associate professor of applied physics at the University of Miyazaki, Japan, said in a statement.

The remnants of Kepler´s supernova lies much closer to the Milky May´s crowded central region than the sun does. The Milky Way´s center experiences faster cycles of star formation and destruction, with stars acquiring more metals with each successive generation. As a result, the star that created Kepler's supernova was probably formed out of material with a higher fraction of metals.

Astronomers can determine a white dwarf's composition by surveying the abundance of certain trace elements, such as manganese.

"Theories indicate that the star's age and metal content affect the peak luminosity of type Ia supernovae," Park explained. "Younger stars likely produce brighter explosions than older ones, which is why understanding the spread of ages among type Ia supernovae is so important."

A supernova is typically the result of two different kinds of binary white dwarf systems. In one type of system, a dominant white dwarf draws material away from a second star. Eventually, the stellar material accumulates until the dominant star becomes unstable.

In the second binary system, the orbits of the two white dwarfs shrink until the two objects merge.

As a white dwarf begins its supernova process, carbon nuclei begin merging together, creating heavier elements and bundles of energy. Eventually, this form of nuclear fusion rapidly spreads throughout the star, ultimately destroying it in a massive explosion that can be picked up by scientific instruments billions of light-years away.

While the researchers were unable to determine which type of binary system triggered the supernova, the study´s results indicate that the white dwarf was probably less than a billion years old when it exploded. By comparison, our sun is about 4.6 billion years old.