Periodic Reporting for period 4 - CSINEUTRONSTAR (The physics and forensics of neutron star explosions)
Reporting period: 2019-12-01 to 2020-05-31
The other part of the project looked at how to use hotspots to determine the nature of the ultradense matter in the cores of neutron stars, using a relativistic ray-tracing based inference technique. We developed a highly-efficient simulation and inference code to do this, and worked closely with nuclear physics colleagues to develop the methodology necessary to map the measured masses and radii to nuclear physics parameters. Using these capabilities we used data from NASA's Neutron Star Interior Composition Explorer (NICER) telescope - installed on the International Space Station in 2017 - to deliver the first mass-radius measurements obtained with this new technique. These results are already being used, in combination with constraints from gravitational wave data, to constrain the properties of ultradense nuclear matter. As a by-product, the technique also maps the locations of the magnetic polar caps on the star - to our surprise these indicated that the field was very far from the simple dipole magnetic field often assumed in pulsar studies, posing new challenges for theorists.
We have published our results in just over 30 refereed journal papers, including an Astrophysical Journal Letters Focus Issue on the NICER results.
It has also delivered viable models for the burst oscillation mechanism. Further investigation will be required to pin this down, but we have identified the important physical processes that need to be included in the modelling.