White dwarfs are among the most stable of stars. Left on their own, these stars that have exhausted most of their nuclear fuel — while still typically as massive as the Sun — and shrunk to a relatively small size 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 it is generally accepted by astronomers 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.
This new composite image shows G344.7-0.1, a supernova remnant created by a Type Ia supernova, through the eyes of different telescopes. X-rays from NASA’s Chandra X-ray Observatory (blue) have been combined with infrared data from NASA’s Spitzer Space Telescope (yellow and green) as well as radio data from the NSF’s Very Large Array and the Commonwealth Scientific and Industrial Research Organisation’s Australia Telescope Compact Array (red).
Astronomers estimate that G344.7-0.1 is about 3,000 to 6,000 years old in Earth’s time frame. On the other hand, the most well-known and widely-observed Type Ia remnants, including Kepler, Tycho, and SN 1006, have all exploded within the last millennium or so as seen from Earth. Therefore, this deep look at G344.7-0.1 with Chandra gives astronomers a window into an important phase later in the evolution of a Type Ia supernova remnant.
Both the expanding blast wave and the stellar debris produce X-rays in supernova remnants. As the debris moves outward from the initial explosion, it encounters resistance from surrounding gas and slows down, creating a reverse shock wave that travels back toward the center of the explosion. This process is analogous to a traffic jam on a highway, where as times passes an increasing number of cars will stop or slow down behind the accident, causing the traffic jam to travel backwards. The reverse shock heats the debris to millions of degrees, causing it to glow in X-rays.
Type Ia remnants like Kepler, Tycho and SN 1006 are too young for the reverse shock to have time to plausibly travel backwards to heat all of the debris in the remnant’s center. However, the relatively advanced age of G344.7-0.1 means that the reverse shock has moved back through the entire debris field.
A paper describing these results was published in the July 1st, 2020 issue of The Astrophysical Journal and entitled “Element Stratification in the Middle-Aged Type Ia Supernova Remnant G344.7-0.1”. Source of the article: chandra.harvard.edu