Mass distribution of neutron stars in binary systems
Pith reviewed 2026-06-30 00:05 UTC · model grok-4.3
The pith
Super-Eddington accretion model accounts for bimodal neutron star mass distribution in binaries
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We constructed a super-Eddington accretion model for accreting neutron stars and investigated the mass growth and distribution of these stars using the population synthesis method. We find, in our model, the mass growth of NSs depends on the binary orbital period and the mass of the donor star. Our results can successfully account for the bimodal distribution of NS masses. The peak distribution of NS masses at around ~ 1.8 Msun primarily originates from NS binary systems where the donor star mass is less than ~ 1.6 Msun and the orbital period is shorter than 20 days; while, NS systems that may undergo common envelope evolution and these NSs can account for the mass peak at 1.4 Msun.
What carries the argument
Super-Eddington accretion model that sets neutron star mass growth according to binary orbital period and donor star mass inside population synthesis calculations
If this is right
- The higher mass peak near 1.8 solar masses arises mainly from binaries with donor masses under 1.6 solar masses and periods shorter than 20 days.
- The lower mass peak near 1.4 solar masses arises from binaries that experience common envelope evolution.
- The bimodal shape emerges directly from the range of orbital periods and donor masses present in the population.
- Mass retention efficiency varies systematically with these binary parameters under the model assumptions.
Where Pith is reading between the lines
- If correct, the model predicts that the relative heights of the two peaks should change with the distribution of binary periods and donor masses in different stellar populations.
- Direct mass measurements in systems with measured periods shorter than 20 days could provide a targeted test of the higher-mass channel.
- The same framework could be applied to black hole binaries to check whether analogous accretion limits produce similar features in their mass distribution.
Load-bearing premise
The super-Eddington accretion model correctly captures the mass transfer rates, retention efficiency, and accretion limits in neutron star binaries.
What would settle it
A large sample of neutron star masses in binaries with known orbital periods and donor masses that fails to show the predicted association between short-period low-mass-donor systems and the 1.8 solar mass peak would falsify the account.
Figures
read the original abstract
It is known that the mass distribution of the known neutron stars (NSs) exhibits a bimodal pattern. The origin of this distribution remains a subject of debate. We constructed a super-Eddington accretion model for accreting neutron stars and investigated the mass growth and distribution of these stars using the population synthesis method. We find, in our model, the mass growth of NSs depends on the binary orbital period and the mass of the donor star. Our results can successfully account for the bimodal distribution of NS masses. The peak distribution of NS masses at around ~ 1.8 Msun primarily originates from NS binary systems where the donor star mass is less than ~ 1.6 Msun and the orbital period is shorter than 20 days; while, NS systems that may undergo common envelope evolution and these NSs can account for the mass peak at 1.4 Msun.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript constructs a super-Eddington accretion model for accreting neutron stars and applies population synthesis to examine their mass growth and distribution in binaries. It claims that the model reproduces the observed bimodal NS mass distribution, with the ~1.8 M⊙ peak arising primarily from systems having donor masses ≲1.6 M⊙ and orbital periods ≲20 days, while the ~1.4 M⊙ peak is produced by systems that undergo common-envelope evolution.
Significance. If the super-Eddington prescription can be shown to be independently validated rather than adjusted to match the peaks, the result would supply a concrete link between binary-evolution channels and the NS mass bimodality, with implications for accretion physics and population synthesis. The work is potentially significant for astro-ph.SR, but its current impact is constrained by the absence of model equations, calibration details, and robustness tests.
major comments (2)
- [Abstract] Abstract: the central claim that the model 'successfully account[s] for the bimodal distribution' rests on an unvalidated super-Eddington accretion prescription whose mass-transfer rates, retention efficiencies, and limits are not derived, calibrated against observations, or compared to Eddington-limited alternatives; without these, the mapping of short-period, low-mass-donor systems to the 1.8 M⊙ peak cannot be assessed as a prediction rather than a fit.
- [Abstract] Abstract: the attribution of the two peaks to specific donor-mass and orbital-period cuts (and to common-envelope systems) is load-bearing for the headline result, yet the manuscript supplies no parameter values, sensitivity tests, or error analysis for the free parameters (super-Eddington efficiency and common-envelope efficiency); a shift of even a factor of a few in retention efficiency would move the reported mass-growth tracks and remove the bimodality.
minor comments (1)
- [Abstract] The abstract employs approximate symbols (~) for the quoted mass and period thresholds without stating the exact simulation ranges or binning used to define the peaks.
Simulated Author's Rebuttal
We thank the referee for the constructive comments on our manuscript. We address the concerns about the validation of the super-Eddington prescription and the lack of parameter details and sensitivity tests below. We will revise the manuscript accordingly to strengthen the presentation of the model and its robustness.
read point-by-point responses
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Referee: [Abstract] Abstract: the central claim that the model 'successfully account[s] for the bimodal distribution' rests on an unvalidated super-Eddington accretion prescription whose mass-transfer rates, retention efficiencies, and limits are not derived, calibrated against observations, or compared to Eddington-limited alternatives; without these, the mapping of short-period, low-mass-donor systems to the 1.8 M⊙ peak cannot be assessed as a prediction rather than a fit.
Authors: We agree that the manuscript would be improved by a more explicit derivation and presentation of the super-Eddington accretion model. The prescription follows from standard assumptions in the literature allowing accretion rates to exceed the Eddington limit with reduced retention at high rates; we will add the governing equations, the functional form of the retention efficiency, and the applied limits in a dedicated methods subsection. We will also include a direct comparison of NS mass-growth tracks computed with the super-Eddington prescription versus a strictly Eddington-limited case. These additions will allow readers to evaluate whether the mapping to the 1.8 M⊙ peak follows from the model physics rather than from parameter tuning. revision: yes
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Referee: [Abstract] Abstract: the attribution of the two peaks to specific donor-mass and orbital-period cuts (and to common-envelope systems) is load-bearing for the headline result, yet the manuscript supplies no parameter values, sensitivity tests, or error analysis for the free parameters (super-Eddington efficiency and common-envelope efficiency); a shift of even a factor of a few in retention efficiency would move the reported mass-growth tracks and remove the bimodality.
Authors: We accept that the current manuscript lacks an explicit listing of the adopted parameter values and accompanying sensitivity analysis. In the revision we will add a table of all free parameters (including the super-Eddington retention efficiency and common-envelope efficiency) together with their numerical values. We will further include a new subsection reporting sensitivity experiments in which these efficiencies are varied by factors of two; the results show that the bimodal structure and the association of the 1.8 M⊙ peak with short-period, low-mass donors persist, although the precise peak locations shift modestly. These tests and the associated error estimates on the mass distributions will be presented to demonstrate robustness. revision: yes
Circularity Check
No circularity: model applied to population synthesis without reduction to fitted inputs
full rationale
The provided abstract and description show the authors construct a super-Eddington accretion model independently, then apply population synthesis to map mass growth as a function of orbital period and donor mass. The resulting accounting for bimodality is presented as an outcome of that mapping rather than a parameter fit or self-citation chain. No quoted equations or sections demonstrate that the target distribution was used to define retention efficiencies or that a uniqueness theorem from prior self-work forces the result. The derivation chain remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
free parameters (2)
- super-Eddington accretion efficiency
- common-envelope efficiency parameter
axioms (1)
- domain assumption Standard initial mass function and binary orbital-period distribution for the simulated population.
Reference graph
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discussion (0)
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