Astronomers have discovered a new type of supernova, or star explosion, and it provides a new window into the violent life cycle of stars. The new research, focused on supernova 2018zd, confirms a prediction made by University of Tokyo astronomer Ken’ichi Nomoto more than 40 years ago.
Amateur astronomer Koichi Itagaki in Japan observed supernova 2018zd in March 2018, spurring astronomers to use telescopes to study it about three hours after it occurred. The supernova happened about 31 million light-years from Earth and archival images from the Hubble and Spitzer space telescopes allowed scientists to see the faint star prior to explosion. This was the first time astronomers were able to see a star like this before and after going supernova.
The main support that prevents stars from collapsing beneath the weight of their own gravity is the energy in their core.
Typically, supernovae occur in two flavors. During a core-collapse supernova, a massive star (more than 10 times the mass of our sun) exhausts its fuel and the star’s core caves in to a black hole or a dense remnant called a neutron star. The other type is called a thermonuclear supernova, and it occurs when a low-mass star remnant called a white dwarf – usually less than eight times the mass of our sun – explodes after pulling matter from a companion star into itself.
But what happens to star between eight and 10 solar masses, such as the star involved in supernova 2018zd? They explode a little differently.
This third, previously unobserved type is referred to as an electron capture supernova – and it was orginally described by Nomoto in 1980. As the star’s core loses fuel, gravitational forces push the core’s electrons and fuse them with atomic nuclei. This sudden drop in electron pressure triggers a collapse and the star buckles beneath its own weight. What remains is a dense neutron star with a little more mass than our sun.
A study based on the new research published Monday in the journal Nature Astronomy.