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Evolutionary Links: From Gaia Neutron Star Binaries to Pulsar White Dwarf Endpoints

Debatri Chattopadhyay, Kyle A. Rocha, Seth Gossage, Vicky Kalogera

TL;DR

This paper addresses how Gaia’s wide, eccentric NS–MS binaries fit into binary-evolution pathways and their connection to the observed MSP–WD population. It combines POSYDON population synthesis with detailed MESA binary evolution, explicitly modeling eccentric mass transfer versus circular RLOF and imposing an Eddington-limited accretion cap. The key findings are that Gaia-like NS–MS systems are rare in isolated channels but consistent with detections under continuous star formation, that eccentric mass transfer yields wide, mildly recycled NS–He WD remnants, and that circular RLOF produces tighter, fully recycled MSP–WD binaries with a subset forming CO WDs. Overall, the work argues that CE recycling remains a dominant formation path for most MSP–WDs, while Gaia-like systems test mass-transfer physics in eccentric binaries and offer a complementary view of neutron-star recycling and WD formation with potential observational consequences for future surveys.

Abstract

The discovery of wide, eccentric Gaia neutron stars (NSs) in binaries with still evolving (likely main sequence) companions offers a new probe of mass transfer and pulsar recycling beyond the compact-binary regime. We model their origins and fates using population synthesis with POSYDON and detailed binary evolution with MESA, contrasting two limiting prescriptions at Roche-lobe overflow (RLOF): enforced circularization versus explicitly eccentric mass transfer. Our MESA setups include updated treatments of eccentric, non-conservative transfer, magnetic-braking torques for cool stars, and neutron-star spin evolution with accretion and dipole spindown. Under optimistic assumptions, isolated evolution yields Gaia-like systems at only <1.5% relative rates of NS-evolving companion binaries, yet absolute numbers remain consistent with detections for continuous star formation. Synthetic populations indicate that many canonical millisecond pulsar-white dwarf (WD) binaries arise from unstable mass transfer and common envelope recycling, whereas Gaia systems typically avoid common envelope and only undergo stable mass transfer. In the case of capping accretion onto the NS at the Eddington rate, circular RLOF keeps the donor's mass-loss rate hovering around the Eddington limit and sustained over long timescales. Eccentric mass transfer instead produces briefer bursty signatures where the donor's mass-loss rate can climb up to a thousand times higher than in the circular case. The eccentric channel then leaves wide, eccentric NS-helium WD binaries with only mild recycling, whereas the circular channel yields long-lived transfer, circular NS-WD binaries (helium or carbon-oxygen core), and fully recycled millisecond pulsars.

Evolutionary Links: From Gaia Neutron Star Binaries to Pulsar White Dwarf Endpoints

TL;DR

This paper addresses how Gaia’s wide, eccentric NS–MS binaries fit into binary-evolution pathways and their connection to the observed MSP–WD population. It combines POSYDON population synthesis with detailed MESA binary evolution, explicitly modeling eccentric mass transfer versus circular RLOF and imposing an Eddington-limited accretion cap. The key findings are that Gaia-like NS–MS systems are rare in isolated channels but consistent with detections under continuous star formation, that eccentric mass transfer yields wide, mildly recycled NS–He WD remnants, and that circular RLOF produces tighter, fully recycled MSP–WD binaries with a subset forming CO WDs. Overall, the work argues that CE recycling remains a dominant formation path for most MSP–WDs, while Gaia-like systems test mass-transfer physics in eccentric binaries and offer a complementary view of neutron-star recycling and WD formation with potential observational consequences for future surveys.

Abstract

The discovery of wide, eccentric Gaia neutron stars (NSs) in binaries with still evolving (likely main sequence) companions offers a new probe of mass transfer and pulsar recycling beyond the compact-binary regime. We model their origins and fates using population synthesis with POSYDON and detailed binary evolution with MESA, contrasting two limiting prescriptions at Roche-lobe overflow (RLOF): enforced circularization versus explicitly eccentric mass transfer. Our MESA setups include updated treatments of eccentric, non-conservative transfer, magnetic-braking torques for cool stars, and neutron-star spin evolution with accretion and dipole spindown. Under optimistic assumptions, isolated evolution yields Gaia-like systems at only <1.5% relative rates of NS-evolving companion binaries, yet absolute numbers remain consistent with detections for continuous star formation. Synthetic populations indicate that many canonical millisecond pulsar-white dwarf (WD) binaries arise from unstable mass transfer and common envelope recycling, whereas Gaia systems typically avoid common envelope and only undergo stable mass transfer. In the case of capping accretion onto the NS at the Eddington rate, circular RLOF keeps the donor's mass-loss rate hovering around the Eddington limit and sustained over long timescales. Eccentric mass transfer instead produces briefer bursty signatures where the donor's mass-loss rate can climb up to a thousand times higher than in the circular case. The eccentric channel then leaves wide, eccentric NS-helium WD binaries with only mild recycling, whereas the circular channel yields long-lived transfer, circular NS-WD binaries (helium or carbon-oxygen core), and fully recycled millisecond pulsars.

Paper Structure

This paper contains 7 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results and Implications
  4. Past with POSYDON
  5. Evolutionary fate with MESA
  6. Connection to Pulsar White Dwarfs
  7. Conclusions and Future Work(s)

Figures (2)

  • Figure 1: Time evolution of key binary and stellar properties for Gaia NS-MS J1553-6846 with the NS mass at 1.323 $M_\odot$, companion of 1.04 $M_\odot$, $P_\mathrm{orb}=310.17\,d$, $e=0.5314$ at solar metallicity comparing the evolution for Eddington-limted circular (cir–Ed, pink ) and eccentric (e-Ed, blue) mass transfers. Panels from top to bottom show: (a) orbital eccentricity $e$; (b) $log_{10}(P_{\rm orb}/{\rm d})$; (c) mass-transfer rate log$_{10}(\dot M/M_\odot\,\mathrm{yr}^{-1})$. All quantities are plotted versus time since RLOF, $t - t_{\rm RLOF} (yr)$.
  • Figure 2: Spin‐period $P_\mathrm{spin}$ versus spin‐down rate $\dot{P}_\mathrm{spin}$ right at the end of stable mass transfer (MT) for four representative pulsar models around 'fiducial" (initial $P_\mathrm{spin}=50\,$ms, initial surface magnetic field $B_0=10^{11}\,$G, magnetic field decay timescale $\tau=$1000 Myr, magnetic field decay mass scale $\kappa=0.025\,$Myr), and the following three with $B_0=10^{12}\,$G, $\kappa=0.025\,$Myr, $\tau=$5000 Myr and all other parameters remain identical to fiducial (in different colour shades) chosen to maximise differences. Each model has 21 Gaia systems, e-Ed (blue, upright triangle, only has He WDs) and cir-Ed (pink, inverted triangle for He WD and circle for CO WD). The radio pulsar observations are depicted as green star (He WD) and gold star (CO/ONe WD). The grey arrows show the eventual time evolution of the pulsars since mass transfer that takes them towards the radio-quiet 'death valley' bordered by the two pulsar 'Death Lines'.