Stability and instability of strange dwarfs

Aims. More than 20 years ago, the existence of stable white dwarfs with a core of strange quark matter was proposed. More recently, via the study of radial modes, it has been concluded instead that such objects are unstable. We aim to clarify this issue. Methods. We investigated the stability of these objects by looking at their radial oscillations while incorporating boundary conditions at the quark"hadron interface, which correspond to either a rapid or a slow conversion of hadrons into quarks. Results. Our analysis shows that objects of this type are stable if the star is not strongly perturbed and ordinary matter cannot transform into strange quark matter because of the Coulomb barrier separating the two components. On the other hand, ordinary matter can be transformed into strange quark matter if the star undergoes a violent process, as in the preliminary stages of a type Ia supernova, and this causes the system to become unstable and collapse into a strange quark star. In this way, the accretion-induced collapse of strange dwarfs can be facilitated, and kilometre-sized objects with sub-solar masses can be produced.