I was looking at the article about Sirius Wikipedia, and it said that Sirius A would become a red giant in about a billion years, then settle down to a white dwarf. I felt this can't be right! If Sirius A becomes a red giant, how long until Sirius B passes the Chandrasekhar limit and becomes a type Ia supernova? Sirius B is relatively heavy for a white dwarf (just under the Sun's mass) and ominously is currently covered in hydrogen. There is a sub-Chandrasekhar limit model for type Ia supernovas that has the star coated in hydrogen which then burns to helium which flashes to start a two explosion supernova. Is that why solar mass and heavier white dwarfs are hard to find? Or just that once a white dwarf starts gaining mass, it soon becomes a supernova? Anyway, if the Sirius system is not going to explode for millions of years, it won't be anywhere near the solar system then. But it is interesting to think that we have a genuine type 1a progenitor close at hand to study.