Astronomers have determined that the remains of a dead star seen in the image above formed from a white dwarf stealing material away from a nearby red giant star.
This picture shows Kepler’s supernova remnant, the leftover entrails of a grizzly stellar death. It is named from astronomer Johannes Kepler, who observed the explosive supernova that formed it in 1604. New data from NASA’s Chandra X-ray observatory has shown a disk-shaped structure near the remnant’s center and a great deal of magnesium in the object.
These two clues provide very important insights into exactly how the star that formed Kepler’s remnant died. At the end of most stars’ lives, they shed their outer layers and leave behind a concentrated core known as a white dwarf. These exotic objects are typically the size of Earth but with the mass of our sun, making them extremely dense — just a teaspoon of white dwarf material would weigh 15 tons.
This weighty burden makes white dwarfs somewhat unstable. If one gains material, by let’s say stealing it from a companion star, and goes above 1.4 times the mass of the sun, it will rapidly collapse, heat up, and then explode in a Type 1a supernova. Because this process occurs once a particular known mass limit is reached, Type 1a supernovas appear almost identical to one another, and their explosion always produces the same brightness. By watching for such standard bursts, astronomers figure out how far different galaxies in the universe are from our own, allowing them to determine how fast the universe is expanding or even accelerating in its expansion.
It is still an open question how most white dwarfs turn into Type 1a supernovas. Some scientists think the event is triggered when two white dwarf cores slam into one another, going over their stable limit and detonating. The new Chandra data suggests that, at least in the case of Kepler’s remnant, the white dwarf grabbed material from its companion star. The disk-shaped structure seen near the center suggests that the supernova explosion hit a ring of gas and dust that would have formed, like water circling a drain, as the white dwarf sucked material away from its neighbor. In addition, magnesium is not an element formed in great abundances during Type 1a supernovas, suggesting it came from the companion star. Whether or not Kepler’s supernova is a typical case remains to be seen.