A strange star scenario for the formation of isolated millisecond pulsars

• Published in: Astronomy and astrophysics (Berlin) 2020-01, Vol.633, p.A45
• Main Authors: Jiang, Long, Wang, Na, Chen, Wen-Cong, Li, Xiang-Dong, Liu, Wei-Min, Gao, Zhi-Fu
• Format: Article
• Language: English
• Subjects: Binary stars; Critical mass; Delay time; Deposition; Galaxies; Millisecond pulsars; Neutron stars; Neutrons; Phase transitions; X ray binaries; X ray stars
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201935132

According to the recycling model, neutron stars in low-mass X-ray binaries were spun up to millisecond pulsars (MSPs), which indicates that all MSPs in the Galactic plane ought to be harbored in binaries. However, about 20% Galactic field MSPs are found to be solitary. To interpret this problem, we assume that the accreting neutron star in binaries may collapse and become a strange star when it reaches some critical mass limit. Mass loss and a weak kick induced by asymmetric collapse during the phase transition (PT) from neutron star to strange star can result in isolated MSPs. In this work, we use a population-synthesis code to examine the PT model. The simulated results show that a kick velocity of ∼60 km s −1 can produce ∼6 × 10 3 isolated MSPs and birth rate of ∼6.6 × 10 −7  yr −1 in the Galaxy, which is approximately in agreement with predictions from observations. For the purpose of comparisons with future observation, we also give the mass distributions of radio and X-ray binary MSPs, along with the delay time distribution.