Neutron stars are fantastic cosmic laboratories to study the most extreme physics. Their intense gravitational fields can provide tests of general relativity and other theories of gravitation. Their unmatched magnetic fields permit studies of the interaction between matter and these fields. And their extreme interior densities allow us to probe matter in regimes not accessible to Earth laboratories.  

 

Observationally, their surface emission provides insight on the physics in their interior. The environment around neutron star also provides a wealth of information, especially to study extreme gravity and the physics of accretion.  In this talk, I will present some of my work on different classes of neutron stars to study various aspects of the extreme physics. This includes studies to constrain the radius of neutron stars, and studies perform wit the recently launched Neutron Star Interior Composition ExploreR (NICER). Throughout the talk, I will address future prospects with upcoming high-energy observatories, such as the ATHENA X-ray Observatory.