QED signatures in thermal emission from the surface of magnetic neutron stars
Neutron stars are unique laboratories for testing our understanding of fundamental physics, from nuclear and particle physics to superconductors and superfluids to gravitational waves. Key instruments for studying neutron stars are X-ray telescopes because the surface/photosphere of neutron stars emit hot thermal radiation at X-ray energies. Most neutron stars are also inferred to have extreme surface magnetic fields (B~10^12 G and even higher). At these field strengths, the vacuum can become birefringent, and radiation is highly polarized. Here I describe the physics of neutron star photospheres and how X-ray polarization observations could detect signatures of quantum electrodynamics, as well as allow us to directly measure the magnetic field of neutron stars.