April 14, 2009

Scientists Explain Youthful Ia Supernovae

Scientists have developed a new explanation for how youthful type Ia supernovae are formed.

Dr. Bo Wang and colleagues from the Yunnan Observatory of the Chinese Academy of Sciences created a new model that links the formation of type Ia supernovae to the transfer of a material from a helium star to a white dwarf companion.

White dwarves are dense remnants of stars like the Sun. Scientists theorize that these white dwarves borrow matter from a nearby star. Once the mass of the remnant star exceeds the Chandrasekhar limit of 1.4 times the mass of the Sun, it collapses and undergoes a runaway nuclear fusion reaction, exploding and releasing a vast amount of energy as a type Ia supernova.

Since the result is notably bright, astronomers have used it as an indicator of distance in space.

Scientists previously showed that type Ia supernovae are increasingly common and about half of them explode less than 100 million years after the formation of their host galaxy's main star.

Dr. Wang's team set out to create a model to explain what may cause youthful supernovae to occur.

Wang and colleagues utilized a stellar evolution computer code, making calculations for about 2600 binary systems consisting of a white dwarf star and a nearby helium star.

When the companion star was a helium star, the white dwarf could transfer mass at a faster rate, which explains why a supernova event could occur in less than 100 million years, researchers wrote in Monthly Notices of the Royal Astronomical Society.

Before this investigation, there was no model which could produce a large population of such young Type Ia supernovae, and no knowledge of a way to produce such numbers," study co-author Xuefei Chen told BBC News.

"A significant population of young Type Ia supernovae may have an effect on models of galactic chemical evolution, since they would return large amounts of iron to the interstellar medium much earlier than previously thought."

"It may also have an impact on cosmology, as they are used as cosmological distance indicators," Chen said.

The next step for the team is to model the properties of the companion helium stars during the time of supernova explosions. They will utilize the Large sky Area Multi-Object fiber Spectral Telescope (LAMOST) to confirm their observation.

"Type Ia supernovae are a key tool to determine the scale of the Universe so we need to be sure of their properties. Our work shows that they can take place early on in the life of the galaxy they reside in," said researcher Dr. Zhanwen Han.


Image Caption: Multiwavelength X-ray / infrared image of SN 1572 or Tycho's Nova, the remnant of a Type Ia supernova.[1] (NASA/CXC/JPL-Caltech/Calar Alto O. Krause et al.)


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