Searching for new physics with X-rays from compact stars

A class of hypothetical particles known as axions are predicted to exist in nature by several compelling theories of elementary particle physics. Axions couple extremely weakly to regular matter, making them challenging to probe in the laboratory. However, axions should be produced in the dense environments of compact stars. Stellar axion emission provides an additional cooling channel that leads to well-known constraints on the axion’s couplings to matter. These constraints are indirect, and although compact stars are predicted to “glow” in axions, this radiation is invisible to us. In this talk I will discuss how the axion radiation is converted into X-ray emission in the strong magnetic field that surrounds many compact stars, thereby providing a new strategy for probing axions through X-ray observations of white dwarfs and neutron stars.