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Happy December Solstice, everybody! ☀️

As the star ages, it starts producing heavy elements like oxygen, neon and magnesium in its core and these accumulate in their cores, being supported just by the sheer pressure between the electrons compressed to insane densities. When the mass of the core surpasses a critical limit, the magnesium and neon atoms start capturing the electrons and using them to convert protons to neutrons and producing neutrinos. As the electrons are removed, the electron pressure that supports the core drops. As it loses support, the core quickly collapses.

As it collapses, the temperature rises and causes the oxygen in the outer layers to ignite, starting a fusion runway reaction. Which the explosion resulting tearing the star apart. This process makes electron capture supernovas an intermediate type between thermal runaway and core collapse supernovas. While creating a very distinct chemical signature of the new elements formed in the supernova that has just been observed in SN2018zd.

Electron-capture supernova is a new third type of supernova theorized to explain the strange composition of some supernova remnants observed, like the Crab Nebula. Affecting stars that are just on the edge where supernovas are expected to happen, between 8 and 10 solar masses.

The two most common types of supernovas are the thermal runaway supernova and the core collapse supernova. Thermal runaway supernovas are formed when white dwarfs increase their mass beyond a critical limit and ignite a runaway fusion reaction that completely disrupts the star, be it by transferring mass from another star, or by the merger of two white dwarfs.

Core collapse supernovas, on the other paw, are created when massive stars, with masses beyond 10 solar masses, start producing iron in their cores, stopping the fusion process that generates the heat that supports the pressure in the core of the star. Quickly, the star falls into itself, compressing the core into a neutron star, and releases insane amounts of energy as neutrinos, which then power the shock wave that disrupts the star.