#Astro # Past the Type IIs ## Type Ia Supernovae Most stars form in binaries. Yes, I may be scrounging for reasons to believe our sun's special in some way, but it's true! Although many binaries have stars with very, very similar masses, most have differentiated star masses - there could be a binary system with an A type star and M type companion (like in HIP 81208, for example!). When one of these stars evolves into a white dwarf, it tends to sit around for the remainder of its "life". That is, unless the other companion becomes a red giant. For certain binary systems, the orbits of the two stars are so close together that when the secondary companion becomes a red giant, the white dwarf may accrete mass from its expanded envelope. This means the white dwarf will get heavier and heavier, as hydrogen and helium fusion occurs on a very thin shell/disk around itself. Eventually, this white dwarf becomes so massive that is passes the **Chandrasekhar Limit**, or 1.4 solar masses, allowing it to ignite carbon fusion. This sudden increase in radiative pressure, coupled with the nature of electron degeneracy pressure not being an inwards-acting force, leads the white dwarf to implode violently. Below is a light spectrum for a type 1a supernova. You can see an initial increase in luminosity followed by a gradual deprecation in brightness over a timespan of 40 days. ![[Pasted image 20230711134828.png]] It's actually known that every white dwarf emits the same amount of light when they go supernova - this is as the mass of carbon actually fusing is always the same, at 1.4 solar masses, meaning the energy released by fusion is always equal.