Since Castor is in it’s red giant stage and is actually 6 stars combined, currently it would become either a black hole or neutron star. This is currently undecided as it is hard to tell in this current stage, Castor is a mass made up of 6 stars, which makes it even harder to decide what will happen after the first supernova, assuming there will be 6 of them. As each star goes through it’s supernova they can become a black hole, if even the first star going through it’s supernova turns into a black hole the gravity from it would pull all the matter around it into it, causing Castor to completely
