The Neutron Star Mass Distribution

Abstract

In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double neutron star and neutron star-white dwarf systems show consistent respective peaks at 1.33 M ⊙ and 1.55 M ⊙ suggesting significant mass accretion (∆m ≈ 0.22 M ⊙ ) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ∼ 2.1 M ⊙ for NSs with white dwarf companions which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M ⊙ limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare super-massive NSs is possible.

The Green Bank North Celestial Cap Pulsar Survey. III. 45 New Pulsar Timing Solutions

“…The two inclination estimates are allowed, since the mass function depends on i sin only and therefore yields no constraint on the sign of i cos . The masses of both stars and their mass ratio are similar to those in most other DNS systems (Kiziltan et al 2013). …”

“…The well-known double neutron star (DNS) system PSR B1913+16 provided the first observational evidence for the existence of gravitational waves (GWs; Taylor & Weisberg 1989;Weisberg et al 2010), and the double pulsar system J0737−3039 continues to place ever more stringent constraints on deviations from general relativity (GR) in the strong-field regime (Kramer et al 2006). Neutron star mass measurements can be used to study nuclear physics and the equation of state of ultradense matter (Demorest et al 2010) while also providing insight into the mass distribution of the neutron star population (Özel et al 2012;Kiziltan et al 2013;Antoniadis et al 2016) and, in turn, formation mechanisms and evolution (e.g., Lattimer & Prakash 2004;Tauris & Savonije 1999). Proper-motion measurements can be used to estimate transverse velocity, which also informs theories of neutron star formation and supernova energetics (Ferdman et al 2013).…”

A preliminary look at the empirical mass distribution of hot B subdwarf stars

“…In this, we follow part of the discussion presented by Kiziltan et al (2010) on the mass distribution of neutron stars, a paper that we found particularly enlightening. Following these authors, we built a likelihood function for a normal mass distribution characterized by a mean value μ and a standard deviation σ,…”

On the formation of galactic black hole low-mass X-ray binaries

“…The BH masses in the 24 XRBs have been dynamically measured to be in the range of ∼ 2.7 M⊙ to 15 M⊙ (Casares & Jonker 2014, and references therein). However, there is statistical evidence for the presence of a dearth of NSs or BHs with masses ∼ 2 − 5M⊙ (Bailyn et al 1998;Özel et al 2010Farr et al 2011;Kreidberg et al 2012;Kiziltan et al 2013). This is in contrast with the traditional thought that the distribution of BH masses should decay with mass (e.g., Fryer 1999;Fryer & Kalogera 2001), suggesting that the physics of SN explosions that lead to the formation of BHs is still unclear Belczynski et al 2012).…”