  A neutron star was first detected as a pulsar in 1967. It is one of the most
mysterious compact objects in the universe, with a radius of the order of 10 km
and masses that can reach two solar masses. In fact, neutron stars are star
remnants, a kind of stellar zombies (they die, but do not disappear). In the
last decades, astronomical observations yielded various contraints for the
neutron star masses and finally, in 2017, a gravitational wave was detected
(GW170817). Its source was identified as the merger of two neutron stars coming
from NGC 4993, a galaxy 140 million light years away from us. The very same
event was detected in $\gamma$-ray, x-ray, UV, IR, radio frequency and even in
the optical region of the electromagnetic spectrum, starting the new era of
multi-messenger astronomy. To understand and describe neutron stars, an
appropriate equation of state that satisfies bulk nuclear matter properties is
necessary. GW170817 detection contributed with extra constraints to determine
it. On the other hand, magnetars are the same sort of compact objects, but
bearing much stronger magnetic fields that can reach up to 10$^{15}$ G on the
surface as compared with the usual 10$^{12}$ G present in ordinary pulsars.
While the description of ordinary pulsars is not completely established,
describing magnetars poses extra challenges. In this paper, I give an overview
on the history of neutron stars and on the development of nuclear models and
show how the description of the tiny world of the nuclear physics can help the
understanding of the cosmos, especially of the neutron stars.
