Probing Extreme Gravity with NICER

The X-ray emission of hot spots on the surface of neutron stars is the prime target of the Neutron star Interior Composition Explorer (NICER). These pulse profiles encode information about the strong gravitational fields generated by these stars. Given NICER's unprecedented spectral and timing resolutions, can we use its observations to perform precision tests of gravity? Can we use its observations to test modifications to General Relativity proposed to address far-reaching issues as dark energy or predicted by the low-energy limits of quantum gravity theories? We will report the status of an ongoing program to answer these questions and show that NICER can, in principle, constrain strong-gravity phenomena predicted by scalar-tensor theories of gravity.