Neutron star pulse profiles in scalar-tensor theories of gravity

TL;DR

This paper develops a toolkit to model neutron star pulse profiles in scalar-tensor gravity, revealing how scalar fields can significantly alter observable signals and offering a new way to test gravity theories with upcoming x-ray data.

Contribution

It provides the first comprehensive toolkit for modeling neutron star pulse profiles in scalar-tensor theories, highlighting deviations from General Relativity.

Findings

Scalar fields significantly modify pulse profiles.

Potential to constrain scalar-tensor theories with x-ray data.

Deviations from General Relativity could be detectable.

Abstract

The observation of the x-ray pulse profile emitted by hotspots on the surface of neutron stars offers a unique tool to measure the bulk properties of these objects, including their masses and radii. The x-ray emission takes place at the star's surface, where the gravitational field is strong, making these observations an incise probe to examine the curvature of spacetime generated by these stars. Motivated by this and the upcoming data releases by x-ray missions, such as NICER (Neutron star Interior Composition Explorer), we present a complete toolkit to model pulse profiles of rotating neutron stars in scalar-tensor gravity. We find that in this class of theories the presence of the scalar field affects the pulse profile's overall shape, producing strong deviations from the General Relativity expectation. This finding opens the possibility of potentially using x-ray pulse profile data to obtain new constraints on scalar-tensor gravity, if the pulse profile is found to be in agreement with General Relativity.