2023ApJ...950..186Z

It is of great interest to understand the equation of state (EOS) of the neutron star, whose core includes highly dense matter. However, there are large uncertainties in the theoretical predictions for the EOS of a neutron star. It is useful to develop a new framework, which is flexible enough to consider the systematic error in theoretical predictions and to use them as a best guess at the same time. We employ a deep neural network to perform a nonparametric fit of the EOS of a neutron star using currently available data. In this framework, the Gaussian process is applied to represent the EOSs and the training set data required to close physical solutions. Our model is constructed under the assumption that the true EOS of a neutron star is a perturbation of the relativistic mean-field model prediction. We fit the EOSs of neutron star using two different example data sets, which can satisfy the latest constraints from the massive neutron stars, NICER, and the gravitational wave of the binary neutron stars. Given our assumptions, we find that a maximum neutron star mass is ${2.38}_{-0.13}^{+0.15}{M}_{\odot }$ or ${2.41}_{-0.14}^{+0.15}{M}_{\odot }$ at the 95% confidence level from two different example data sets. It implies that the 1.4M_⊙ radius is ${12.31}_{-0.31}^{+0.29}$ or ${12.30}_{-0.37}^{+0.35}$ km. These results are consistent with results from previous studies using similar priors. It has demonstrated the recovery of the EOS of NS using a nonparametric model.