  One very promising technique for measuring the dense matter Equation of State
exploits hotspots that form on the neutron star surface due to the pulsar
mechanism, accretion streams, or during thermonuclear explosions in the neutron
star ocean. This article explains how Pulse Profile Modeling of hotspots is
being used by the Neutron Star Interior Composition Explorer (NICER), an X-ray
telescope installed on the International Space Station in 2017 - and why the
technique is a mission driver for the next, larger-area generation of
telescopes including the enhanced X-ray Timing and Polarimetry (eXTP) mission
and the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays
(STROBE-X).
