Probing neutron star interiors and the properties of cold ultra-dense matter with the SKAO

TL;DR

This paper discusses how the SKAO will advance our understanding of ultra-dense matter inside neutron stars through radio observations, global property measurements, and exploring new physics like dark matter and modified gravity.

Contribution

It presents the current state of dense matter physics and details how SKAO's capabilities will enable novel constraints on neutron star interiors and ultra-dense matter properties.

Findings

SKAO will improve measurements of neutron star masses and rotation frequencies.

Radio observations will shed light on neutron star superfluidity and dense matter physics.

Synergies with other observatories will enhance constraints on dark matter and gravity models.

Abstract

Matter inside neutron stars is compressed to densities several times greater than nuclear saturation density, while maintaining low temperatures and large asymmetries between neutrons and protons. Neutron stars, therefore, provide a unique laboratory for testing physics in environments that cannot be recreated on Earth. To uncover the highly uncertain nature of cold, ultra-dense matter, discovering and monitoring pulsars is essential, and the SKA will play a crucial role in this endeavour. In this paper, we will present the current state-of-the-art in dense matter physics and dense matter superfluidity, and discuss recent advances in measuring global neutron star properties (masses, moments of inertia, and maximum rotation frequencies) as well as non-global observables (pulsar glitches and free precession). We will specifically highlight how radio observations of isolated neutron stars and those in binaries -- such as those performed with the SKA in the near future -- inform our understanding of ultra-dense physics and address in detail how SKAO's telescopes unprecedented sensitivity, large-scale survey and sub-arraying capabilities will enable novel dense matter constraints. We will also address the potential impact of dark matter and modified gravity models on these constraints and emphasise the role of synergies between the SKA and other facilities, specifically X-ray telescopes and next-generation gravitational wave observatories.