  What if normal baryonic matter is compressed so tightly that atomic nuclei
come into close contact? This question has been asked since 1930s. The fist
answer was presented by Lev Landau whose speculation has been developed, and
the concept of neutron star is then popularized. However, another answer is
related to strange star, which becomes worthy of attention especially after the
establishment of the standard model of particle physics in 1960s. The basic
ideas of this study are introduced pedagogically. We must point out
emphatically that flavour symmetry of and strong coupling between quarks would
be essential in seeking true answer to the question. The final answer is
expected to appear in the era of multimessenger astronomy. It is emphasized too
that, besides the differences of global properties (e.g., mass-radius relation,
maximum mass, tidal deformability), the strong-bound surface of strange star
(rather than the gravity-bound one for conventional neutron star) could play an
important role in identifying a strange star by astronomical observations.
