  In the late age of developing quantum mechanics, Lev Landau, one of the
distinguished players, made great efforts to understand the nature of matter,
even stellar matter, by applying the quantum theory. Ninety years ago, he
published his idea of "neutron" star, which burst upon him during his visit
over Europe in the previous year. The key point that motivated Landau to write
the paper is to make a state with lower energy for "gigantic nucleus", avoiding
extremely high kinematic energy of electron gas due to the new Fermi-Dirac
statistics focused hotly on at that time. Landau had no alternative but to
neutronize/neutralize by "combining a proton and an electron", as electron and
proton were supposed to be elementary before the discovery of neutron. However,
our understanding of the Nature has fundamentally improved today, and another
way (i.e., strangeonization) could also embody neutralization and thus a
low-energy state that Landau had in mind, which could further make
unprecedented opportunities in this multi-messenger era of astronomy. Strangeon
matter in "old" physics may impact dramatically on today's physics, from
compact stars initiated by Landau, to cosmic rays and dark matter. In this
essay, we are making briefly the origin and development of neutron star concept
to reform radically, to remember Landau's substantial contribution in
astrophysics and to recall those peculiar memories.
