Supernovae of type "Ia" are those without helium present, but with evidence of silicon present in the spectrum. The most accepted theory is that this type of supernova is the result of mass accretion on a carbon-oxygen white dwarf from a companion star, usually a red giant. This can happen in very close binary star systems. Both stars have the same age and models indicate that they almost always have a similar mass. But usually one of the stars is more massive than the other and the more massive star evolves faster (leave the main sequence) before the lower mass star does. A star with less than 8-9 solar masses evolves at the end of its life into a white dwarf, binary systems would consist of a white dwarf and a red giant which has greatly expanded its outer layers.
During the explosion an amount of carbon undergoes fusion that a normal star would take centuries to use up. This enormous release of energy creates a powerful shockwave that destroys the star, ejecting all its mass at speeds of around 10,000 km / s. The energy released in the explosion also causes an extreme increase in brightness, so these supernovae become the brightest of all, emitting around 10^44 J (1 foe). Normally there are no traces of the star that caused the cataclysm, but only traces of superheated gas and dust that is rapidly expanding.
What happens to the neighboring star?