The discovery of the most massive neutron star could have wide-ranging impacts across several fields of physics and astrophysics.
"This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out," said Paul Demorest, of the National Radio Astronomy Observatory (NRAO).
"This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics," he added.
A neutron star can be several times more dense than an atomic nucleus, and a thimbleful of neutron-star material would weigh more than 500 million tons – making it an ideal case study for studying the most dense and exotic states of matter known to physics.
The neutron star is a pulsar, emitting lighthouse-like beams of radio waves that sweep through space as it rotates.
This pulsar, called PSR J1614-2230, spins 317 times per second, and the companion completes an orbit in just under nine days. The pair, some 3,000 light-years distant, are in an orbit seen almost exactly edge-on from Earth.
As the orbit carries the white dwarf directly in front of the pulsar, the radio waves from the pulsar that reach Earth must travel very close to the white dwarf.
This close passage causes them to be delayed in their arrival by the distortion of spacetime produced by the white dwarf''s gravitation. This effect, called the Shapiro Delay, allowed the scientists to precisely measure the masses of both stars.
The astronomers followed the binary stars through one complete orbit earlier this year. Their observations revealed it to be twice as massive as the Sun. That much mass, they say, changes their understanding of a neutron star's composition.
The team reported their results in the October 28 issue of the scientific journal Nature.