The two holdouts didn’t want to go to Venus anymore. They wanted to go back to the sun. Why? Because one of them just divided and created the other. Astrophage hang out on the surface of the sun gathering energy via heat. They store it internally in some way no one understands. Then, when they have enough, they migrate to Venus to breed, using that stored energy to fly through space using infrared light as a propellant. Lots of species migrate to breed. Why would Astrophage be any different?
