# Towards Understanding Astrophysical Effects of Nuclear Symmetry Energy

## TL;DR

This paper reviews recent advances in understanding the nuclear symmetry energy's density dependence, crucial for neutron-rich matter in nuclear physics and astrophysics, highlighting progress, challenges, and implications from experiments and observations.

## Contribution

It synthesizes recent theoretical, experimental, and observational progress on the symmetry energy and discusses new challenges in understanding its astrophysical effects.

## Key findings

- Progress in predicting symmetry energy using microscopic theories.
- Experimental and observational probes of symmetry energy have advanced.
- Key challenges remain in constraining symmetry energy at high densities.

## Abstract

Determining the Equation of State (EOS) of dense neutron-rich nuclear matter is a shared goal of both nuclear physics and astrophysics. Except possible phase transitions, the density dependence of nuclear symmetry \esym is the most uncertain part of the EOS of neutron-rich nucleonic matter especially at supra-saturation densities. Much progresses have been made in recent years in predicting the symmetry energy and understanding why it is still very uncertain using various microscopic nuclear many-body theories and phenomenological models. Simultaneously, significant progresses have also been made in probing the symmetry energy in both terrestrial nuclear laboratories and astrophysical observatories. In light of the GW170817 event as well as ongoing or planned nuclear experiments and astrophysical observations probing the EOS of dense neutron-rich matter, we review recent progresses and identify new challenges to the best knowledge we have on several selected topics critical for understanding astrophysical effects of the nuclear symmetry energy.