GW170817 offers astrophysicists new and exciting information about the equation of state (EOS) of neutron stars. The EOS describes the complex behaviour of the dense nuclear matter that makes up neutron stars. Little is currently known about the EOS because it is difficult to glean information from conventional astronomical observations and because theoretical calculations of dense nuclear matter are extremely difficult to do. Before GW170817, the most important piece of information about the EOS came from observations published in 2010 and 2013, which showed that neutron stars can have masses at least as large as two solar masses.
