A massive pulsar in a compact relativistic binary

TLDR: Pulsar J0348+0432 is only the second neutron star with a precisely determined mass of 2 M☉

Abstract: Many physically motivated extensions to general relativity (GR) predict significant deviations at energies present in massive neutron stars. We report the measurement of a 2.01 \(\pm \) 0.04 solar mass (M\(_\odot \)) pulsar in a 2.46-h orbit around a 0.172 \(\pm \) 0.003 M\(_\odot \) white dwarf. The high pulsar mass and the compact orbit make this system a sensitive laboratory of a previously untested strong-field gravity regime. Thus far, the observed orbital decay agrees with GR, supporting its validity even for the extreme conditions present in the system. The resulting constraints on deviations support the use of GR-based templates for ground-based gravitational wave detection experiments. Additionally, the system strengthens recent constraints on the properties of dense matter and provides novel insight to binary stellar astrophysics and pulsar recycling.