Supernova
Electron-capture supernovae

In 1980, a "third type" of supernova was predicted by Ken'ichi Nomoto of the University of Tokyo, called an electron-capture supernova. It would arise when a star "in the transitional range (~8 to 10 solar masses) between white dwarf formation and iron core-collapse supernovae", and with a degenerate O+Ne+Mg core, imploded after its core ran out of nuclear fuel, causing gravity to compress the electrons in the star's core into their atomic nuclei, leading to a supernova explosion and leaving behind a neutron star. In June 2021, a paper in the journal Nature Astronomy reported that the 2018 supernova SN 2018zd (in the galaxy NGC 2146, about 31 million light-years from Earth) appeared to be the first observation of an electron-capture supernova. The 1054 supernova explosion that created the Crab Nebula in our galaxy had been thought to be the best candidate for an electron-capture supernova, and the 2021 paper makes it more likely that this was correct.
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