New observations of the binary millisecond pulsar PSR J1614-2230 have identified one of its components as the most massive neutron star for which a precise mass is known � nearly 20% greater than previous highest values. Neutron stars are composed of the densest form of matter known, and millisecond pulsars are rotating neutron stars. The observed range of neutron star masses has hitherto been too narrow to rule out many predictions of 'exotic' non-nucleonic components, but this pulsar weighs in at around two solar masses, ruling out almost all currently proposed equations of state involving exotic hyperon or boson condensates.

• Nature article (astro-ph version )
• ApJ Article.
• Nature news. "Astrophysics: Weighing in on neutron stars".
• Scientific American "Hard-Core Astrophysics: Massive Neutron Star Hints at How Matter Behaves at Its Densest"