PSR J0024–7204ai: A massive eccentric binary system in the globular cluster 47 Tucanae

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
² Rheinische Friedrich-Wilhelms-Universität Bonn, Regina-Pacis-Weg 3, D-53113 Bonn, Germany
³ Fakultät für Physik, Universität Bielefeld, D-33615 Bielefeld, Germany
⁴ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti 93/2, I-40129 Bologna, Italy
⁵ INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I-40129 Bologna, Italy
⁶ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
⁷ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory 7925, South Africa
⁸ Max Planck Institute for Gravitational Physics (Albert Einstein Institute), D-30167 Hannover, Germany
⁹ Leibniz Universität Hannover, D-30167 Hannover, Germany
¹⁰ National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100101, PR China
¹¹ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218 Hawthorn, VIC 3122, Australia

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. , This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 December 2025
Accepted: 13 February 2026

Abstract

In this paper we present PSR J0024−7204ai, a 13.026-ms binary pulsar recently discovered in the globular cluster 47 Tucanae by the MeerKAT radio telescope. This is the slowest-spinning pulsar known in this globular cluster. It has a ∼1.67-day orbit with an eccentricity of e ≈ 0.18. Although it is not yet possible to derive an unambiguous phase-connected timing solution, by combining detections obtained from MeerKAT and archival Parkes data, we were able to measure the rate of advance of periastron to a high significance: ω˙ = 0.1601 ± 0.0046 deg yr⁻¹. This value implies a total system mass of 2.41 ± 0.11 M_⊙ (68.3% C.L.), which, when combined with the binary mass function, gives a maximum pulsar mass of ∼1.7 M_⊙ and a minimum companion mass of ∼0.7 M_⊙. Apart from being the slowest pulsar in 47 Tucanae, its orbit is by far the most eccentric, and its companion is the most massive among all known binary pulsars in this globular cluster. It is possible that the system is an old millisecond pulsar–carbon-oxygen white dwarf binary whose orbit was perturbed by stellar dynamical interactions in the cluster core. Further follow-up observations of this system will be essential to obtaining a more detailed characterisation of this system and its evolution.