  According to the hypothesis that strange quark matter may be the true ground
state of matter at extremely high densities, strange quark stars should be
stable and could exist in the Universe. It is possible that pulsars may
actually be strange stars, but not neutron stars. Here we present a short
review on recent progresses in the field of strange quark stars. Three popular
phenomenological models widely used to describe strange quark matter are
introduced, with special attention being paid on the corresponding equation of
state in each model. Combining the equation of state with the
Tolman-Oppenheimer-Volkov equations, the inner structure and mass-radius
relation can be obtained for the whole sequence of strange stars. Strong
gravitational wave emissions may be generated by strange stars through various
mechanisms, which may help identify strange stars via observations. Especially,
close-in strange quark planets with respect to their hosts may provide a unique
test for the existence of strange quark objects. Fierce electromagnetic bursts
could also be generated by strange stars. The energy may come from the phase
transition of neutron stars to strange stars, or from the merger of binary
strange stars. The collapse of the strange star crust can also release a huge
amount of energy. It is shown that strange quark stars may be involved in short
gamma-ray bursts and fast radio bursts.
