A remarkably precise observational relation for pulse core component widths of radio pulsars is used to derive stringent limits on pulsar radii , strongly indicating that pulsars are strange stars rather than neutron stars .
This is achieved by inclusion of general relativistic effects due to the pulsar mass on the size of the emission region needed to explain the observed pulse widths , which constrain the pulsar masses to be \leq 2.5 M _ { \odot } and radii \leq 10.5 km .