  Neutron stars are among the main targets for gravitational wave
observatories, however, their equation of state is still not well established.
Mainly phenomenological models with many parameters are widely used by far,
while theoretical models are not so practical. In arXiv:1902.08477, a
theoretical equation of state with only one parameter is derived from
Witten-Sakai-Sugimoto model, as an application of AdS/QCD, where pointlike
instanton case is taken into consideration. When the tidal deformability
constraint from gravitational wave event is satisfied, the maximum mass is
about 1.7 solar masses. Now we upgrade this model to instanton gas, with one
more variable, the instanton width. This is not naively a free parameter, but a
function of the chemical potential. Thus we end up with a more complicated and
accurate model, but still with only one adjustable parameter. In this case, we
find the maximum mass becomes 1.85 solar masses. This is an encouraging result,
as a theoretically derived model.
