Tour: When a Stable Star Explodes

White dwarfs are among the most stable of stars. They are stars that have exhausted most of their nuclear fuel and shrunk to about the size of Earth, yet still contain about the same mass as the Sun. Left on their own, white dwarfs can last for billions or even trillions of years.

However, a white dwarf with a nearby companion star can become a cosmic powder keg. If the companion's orbit brings it too close, the white dwarf can pull material from it until the white dwarf grows so much that it becomes unstable and explodes. This kind of stellar blast is called a Type Ia supernova.

While astronomers generally accept that such encounters between white dwarfs and "normal" companion stars are one likely source of Type Ia supernova explosions, many details of the process are not well understood. One way to investigate the explosion mechanism is to look at the elements left behind by the supernova in its debris or ejecta.

Chandra is one of the best tools available for scientists to study supernova remnants and measure the composition and distribution of "heavy" elements — that is, elements heavier than hydrogen and helium — they contain.

The supernova remnant G344.7-0.1 is useful to study because astronomers think it is about 3,000 to 6,000 years old in Earth's time frame. This makes it significantly older than most of the well-known and widely-observed Type Ia remnants, including Kepler, Tycho, and SN 1006, which have all exploded within the last millennium or so as seen from Earth. By looking deeply at G344.7-0.1 with Chandra, astronomers have a window into an important phase later in the evolution of a Type Ia supernova remnant.

What do the Chandra data reveal? Researchers were able to study the effects of a reverse shock wave that moves backward through the remnant toward its center. This study gives scientists more information about where and when key elements are made during these stellar explosions. There is still much to learn about these objects and Chandra will continue to be an important tool in investigating them.