RESEARCH ARTICLE 

Front. Phys. 15(2), 24603 (2020)

Relation between gravitational mass and baryonic mass for non-rotating and rapidly rotating neutron stars

He Gao¹, Shun-Ke Ai^2,1, Zhou-Jian Cao¹, Bing Zhang², Zhen-Yu Zhu^3,4, Ang Li³, Nai-Bo Zhang⁵, Andreas Bauswein⁶

1. Department of Astronomy, Beijing Normal University, Beijing 100875, China

2. Department of Physics and Astronomy, University of Nevada Las Vegas, NV 89154, USA

3. Department of Astronomy, Xiamen University, Xiamen 361005, China

4. Institute for Theoretical Physics, Max-von-Laue-Strasse 1, 60438 Frankfurt, Germany

5. Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai 264209, China

6. GSI Helmholtzzentrum für Schwerionenforschung, Planckstraβe 1, 64291 Darmstadt, Germany

With a selected sample of neutron star (NS) equations of state (EOSs) that are consistent with the current observations and have a range of maximum masses, we investigate the relations between NS gravitational mass M_g and baryonic mass M_b, and the relations between the maximum NS mass supported through uniform rotation (M_max) and that of nonrotating NSs (M_TOV). We find that for an EOS-independent quadratic, universal transformation formula (M_b=Mg+A×Mg²), the best-fit A value is 0.080 for non-rotating NSs, 0.064 for maximally rotating NSs, and 0.073 when NSs with arbitrary rotation are considered. The residual error of the transformation is ~0.1M_⊙ for non-spin or maximum-spin, but is as large as ~0.2M_⊙ for all spins. For different EOSs, we find that the parameter A for non-rotating NSs is proportional to R_1.4⁻¹ (where R_1.4 is NS radius for 1.4M_⊙ in units of km). For a particular EOS, if one adopts the best-fit parameters for different spin periods, the residual error of the transformation is smaller, which is of the order of 0.01 M_⊙ for the quadratic form and less than 0.01M_⊙ for the cubic form (M_b=Mg+A₁×Mg²+A₂×Mg³). We also find a very tight and general correlation between the normalized mass gain due to spin Δm≡(Mmax−MTOV)/M_TOV and the spin period normalized to the Keplerian period P, i.e., log₁₀Δm=(−2.74±0.05)log10P+log10(0.20±0.01), which is independent of EOS models. These empirical relations are helpful to study NS-NS mergers with a long-lived NS merger product using multi-messenger data. The application of our results to GW170817 is discussed.

全文下载：

http://journal.hep.com.cn/fop/EN/10.1007/s11467-019-0945-9

https://doi.org/10.1007/s11467-019-0945-9