  The recent discovery of a central compact object (CCO) within the supernova
remnant HESS J1731-347, characterized by a mass of approximately
$0.77^{+0.20}_{-0.17} M_{\odot}$ and a radius of about $10.4^{+0.86}_{-0.78}$
km, has opened up a new window for the study of compact objects. This CCO is
particularly intriguing because it is the lightest and smallest compact object
ever observed, raising questions and challenging the existing theories. To
account for this light compact star, a mean-field model within the framework of
parity doublet structure is applied to describe the hadron matter. Inside the
model, part of the nucleon mass is associated with the chiral symmetry breaking
while the other part is from the chiral invariant mass $m_0$ which is
insensitive to the temperature/density. The value of $m_0$ affects the nuclear
equation of state for uniform nuclear matter at low density and exhibits strong
correlations with the radii of neutron stars.
  We point out that HESS J1731-347 can be explained as the lightest neutron
star for $m_0 \simeq 850$\,MeV.
