Does Sub-millisecond Pulsar XTE J1739-285 Contain a Low Magnetic Neutron Star or Quark Star ?

TL;DR

This paper constrains the mass, radius, and magnetic field of the ultra-fast pulsar XTE J1739-285, providing evidence that it may be a strange quark star rather than a neutron star based on observational data and theoretical models.

Contribution

It offers new constraints on the star's properties and suggests the star could be a strange quark star, challenging previous assumptions about neutron star compositions.

Findings

Mass estimated at 1.51 solar masses

Radius constrained to 10.9 km

Magnetic field between 4×10^7 G and 10^9 G

Abstract

With the possible detection of the fastest spinning nuclear-powered pulsar XTE J1739-285 of frequency 1122 Hz (0.8913 ms), it arouses us to constrain the mass and radius of its central compact object and to imply the stellar matter compositions: neutrons or quarks. Spun-up by the accreting materials to such a high rotating speed, the compact star should have either a small radius or short innermost stable circular orbit. By the empirical relation between the upper kHz quasi-periodic oscillation frequency and star spin frequency, a strong constraint on mass and radius is obtained as 1.51 solar masses and 10.9 km, which excludes most equations of states (EOSs) of normal neutrons and strongly hints the star promisingly to be a strange quark star. Furthermore, the star magnetic field is estimated to be about $4\times10^{7} (G) < B < 10^{9} (G) $, which reconciles with those of millisecond radio pulsars, revealing the clues of the evolution linkage of two types of astrophysical objects.