Nonparametric Model for the Equations of State of a Neutron Star from Deep Neural Network

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(circle dot) or 2.41-M-+0.15(0.14)circle dot at the 95% confidence level from two different example data sets. It implies that the 1.4M(circle dot) 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.

Automated summary

Understanding the equation of state (EOS) of neutron stars is important, but there are uncertainties in theoretical predictions. To address this, we use a deep neural network to fit the EOS using available data. Based on our assumptions, we find that the maximum neutron star mass is 2.38-2.41 solar masses, with a radius of 12.30-12.31 km.