The Nebula And The Neutron Star . ... At a distance of 180 light-years it is the closest known neutron star. ... But optical astronomers were surprised to discover that RX J1856.5-3754 is also surrounded by a cone-shaped nebula. ... A faint blue dot near the tip of the cone is the neutron star itself. The nebula appears to have formed very near the surface of the neutron star and astronomers are trying to determine if the observed densities and temperatures can explain the nebula's appearance. ...