Researchers at the University of California at Santa Barbara and the Las Cambres Observatory have discovered a new type of supernova. The discovery confirms the theory that astronomer Kenichi Nomoto put forward 40 years ago, in 1980.
Historically, supernovae are divided into two main types: cataclysmic variable stars (resulting from a thermonuclear explosion of a white dwarf) and stars with a collapsing core (as a result of the rapid compression and subsequent powerful explosion of a massive star, a sharp increase in the luminosity of the star occurs). Between these two main types of supernovae are electron trapping supernovae. These stars stop fusion when their cores are composed of oxygen, neon, and magnesium; they are not massive enough to create iron.
In an electron-trapping supernova, some electrons in the oxygen-neon-magnesium core slam into atomic nuclei in a process called electron capture. This removal of electrons causes the star’s core to bend under its own weight and collapse, leading to an electron-trapping supernova.
Recently, an international team of astronomers observed the first example of a new type of supernova. This discovery confirms the hypothesis made by astronomer Kenichi Nomoto of the University of Tokyo in 1980.
Supernova 2018zd was discovered in the constellation Giraffe in 2018, about three hours after the explosion. It is located 31 million light years from Earth.
At first, scientists assumed that there was a type II supernova in front of them. But, having studied the archival images of the Hubble and Spitzer telescopes, they were able to find a predecessor star. Its brightness and mass turned out to be much less than that of the luminaries that give rise to type II supernovae.
A team of scientists has been collecting data on the star for two years. Then scientists from the University of California at Davis conducted a spectral analysis two years after the explosion. As a result, the researchers found out that the supernova belongs to a new type – an electron-capture supernova.
It also turned out that it fits the six criteria that scientists identified for a new type of supernova back in 1980. It apparently had a supersymptotic giant branch (SAGB) progenitor star. They also saw a strong pre-supernova mass loss, an unusual stellar chemical spectrum, a weak explosion, little radioactivity, and a neutron-rich core.