Arthur T Knackerbracket has found the following story:
Pulsars in binary systems are affected by relativistic effects, causing the spin axes of each pulsar to change their direction with time. A research team led by Gregory Desvignes from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has used radio observations of the source PSR J1906+0746 to reconstruct the polarised emission over the pulsar's magnetic pole and to predict the disappearance of the detectable emission by 2028. Observations of this system confirm the validity of a 50-year old model that relates the pulsar's radiation to its geometry. The researchers are also able to precisely measure the rate of change in spin direction and find an excellent agreement with the predictions of Einstein's general theory of relativity.
The experiment is the most challenging test to date of this important effect of relativistic spin precession for strongly self-gravitating bodies. Moreover, the reconstructed radio beam shape has implications for the population of neutron stars and the expected rate of neutron star mergers as observed by gravitational wave detectors such as LIGO.
Pulsars are fast-spinning neutron stars that concentrate 40 percent more mass than the Sun—or more! – into a small sphere of only about 20 km diameter. They have extremely strong magnetic fields and emit a beam of radio waves along their magnetic axes above each of their opposite magnetic poles. Due to their stable rotation, a lighthouse effect produces pulsed signals that arrive on Earth with the accuracy of an atomic clock. The large mass, the compactness of the source, and the clock-like properties allows astronomers to use them as laboratories to test Einstein's general theory of relativity.
The results are published in Science, issue 6 September 2019.
The theory predicts that spacetime is curved by massive bodies such as pulsars. One expected consequence is the effect of relativistic spin precession in binary pulsars. The effect arises from a misalignment of the spin vector of each pulsar with respect to the total angular momentum vector of the binary system, and is most likely caused by an asymmetric supernova explosion. This precession causes the viewing geometry to vary, which can be tested observationally by monitoring systematic changes in the observed pulse profile.
[...]The team noticed that initially it was possible to observe the pulsar's opposite magnetic poles, when both Northern and Southern beams (referred to as the main pulse and interpulse in the study) were pointed to Earth once per rotation. With time, the Northern beam disappeared and only the Southern beam remained visible. Based on a detailed study of the polarization information of the received emission, it was possible to apply a 50-year old model, predicting that the polarization properties encoded information about the geometry of the pulsar. The pulsar data validated the model and also allowed the team to measure the rate of precession with only 5 percent uncertainty level, tighter than the precession rate measurement in the Double Pulsar system, a reference system for such tests so far. The measured value agrees perfectly with the prediction of Einstein's theory.
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