I will discuss why "neutron stars", i.e. compact objects made of nucleons and of hadronic resonances can exist together with strange quark stars, i.e. objects composed (almost) entirely of quark matter. In particular I will summarize the main observational tests (masses and radii, implications for mergers) and I will discuss the problem of the existence of strangelets, arguing that they can exist but that they are very massive, with a baryonic mass larger than about 10^30.
Margherita Fasano