Understanding the Neutron Star Population with the SKAO telescopes

TL;DR

This paper lays out a comprehensive plan for using the SKAO to census and study the Galactic neutron-star population across diverse subgroups, including magnetars, central compact objects, RRATs, MSPs, and DNS/NS–BH systems. It details observational strategies for SKAO array assemblies AA* and AA4, combining in real-time pulsar searches with extensive timing programs to exploit SKAO's sensitivity, wide field of view, and multi-beam capabilities. Forecasts indicate detections of roughly 10^4 ordinary pulsars and 8×10^2 to 10^3 MSPs, enabling powerful population synthesis, precise NS mass and kick measurements, and stringent tests of gravity and the nuclear equation of state. The work emphasizes multi-wavelength and multi-messenger synergies, advanced data-analysis approaches, and efficient observing strategies to maximize the scientific return from a complete SKAO NS census.

Abstract

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the sample of sources that can be studied, but will undoubtedly also uncover previously unknown types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased known population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar's spin-down related to its radio emission; What is the nuclear equation of state? Increasing the known numbers of pulsars in binary or triple systems may enable both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility to undertake a wide range of neutron star research. In this paper, we give an overview of different types of neutron stars and discuss how the SKAO telescopes will aid in our understanding of the neutron star population.

Figures (7)

• Figure 1: Distribution of 2752 pulsars in the $P-\dot{P}$ diagram. These are all the currently known pulsars that have both period and period derivative values listed. Lines of constant characteristic age and constant surface magnetic field strength are shown. Data taken from the ATNF Pulsar Catalogue version 2.6.1 in June 2025 Manchester2005.
• Figure 2: Time series (all of equal duration) taken from Burke-Spolaor2013 showing radio emission from a variety of sources (top to bottom: the Vela pulsar, PSR J1646--6831 (a nulling pulsar), RRAT J1647--36 and RRAT J1226--32). The binary scales show an estimated representation of the null/emission state.
• Figure 3: $P$-$\dot{P}$ diagrams for the expected population of isolated pulsars observed with SKAO in the AA* (left) and AA4 (right) configurations corresponding to Survey Option 3 for the evolutionary population synthesis approach outlined in Keane2025_SKA_Census. We show the currently observed population in blue (data taken from the ATNF Pulsar Catalogue v2.5.1; Manchester2005, https://www.atnf.csiro.au/research/pulsar/psrcat/), and pulsars detected with SKAO Low and Mid Band 2 in yellow and orange, respectively. Lines of constant rotational energy loss and dipole magnetic field strength are shown in grey. The black lines show extreme versions of the pulsar death lines below which radio emission has been proposed to cease and delimit the so-called "death valley" shaded in grey Chen1993. Note that these population synthesis simulations take into account the natural fading of the radio emission but do not account for sudden emission switch-off or occasional switch-on of stronger emission that may be detectable with single-pulse searches (for a recent example, see Rajwade2025arXiv).
• Figure 4: Distribution of 346 binary radio pulsars in the $P\dot{P}$-diagram. The nature of the companion stars is indicated with different symbols. Isolated pulsars are represented with a dot. Lines of constant surface B-field flux density are shown. Data taken from the ATNF Pulsar Catalogue version 2.6.0 in February 2025 Manchester2005.
• Figure 5: Distribution of spins of 485 radio MSPs with $P < 10\;{\rm ms}$. After tv23.