A team of astronomers at the University of California have discovered a white dwarf that survived a supernova explosion rather than completely disintegrating. The results of the study were published in The Astrophysical Journal.
Supernova SN 2012Z is a Type Ia supernova when a white dwarf explodes in a binary system. A supernova is thought to occur when a white dwarf pulls in too much material, causing fusion reactions to occur in its interior. SN 2012Z was a variation of this type, called Iax, which features a less powerful thermonuclear explosion.
The supernova was first detected in 2012 in the nearby spiral galaxy NGC 1309, 100 million light-years from Earth. As the experts found out, the explosion was not powerful enough to eject all the material of the outer layers of the star into space, so some of it fell back onto the remnant. As a result, the white dwarf has grown in size and become brighter. It is expected that in the future the star will become less massive, but larger.
For decades, scientists believed that Type Ia supernovae explode when a white dwarf reaches a certain size limit, called the Chandrasekhar limit, at which it is 1.4 times the mass of the Sun. This model has become less popular over the past few years as many Type Ia supernovae have been found to be below the mass limit, and new theoretical models have shown that there are other causes for explosions. The authors of the study believe that SN 2012Z occurred precisely when the limit was reached.