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Kinematic Evidence for Open Cluster Origins of Galactic Binary Neutron Stars

Wen-Jie Yu, Lu Zhou, Zhi-Qiang You, Hao Ding, Lu Li, Long Wang, Xing-Jiang Zhu

Abstract

We investigate the potential birthplace of Galactic binary neutron star (BNS) systems through a kinematic analysis. Using high-precision astrometry from Gaia DR3, updated pulsar distances, and Monte Carlo sampling of astrometric errors, we integrate the past trajectories of 11 Galactic BNSs and 167 globular clusters plus 2967 open clusters, to search for past encounters. Our results suggest that BNS origin in globular clusters is unlikely, with low encounter probabilities (e.g., $\lesssim 0.5\%$ for NGC 5139) and requiring excessive ejection velocities. Conversely, our analysis indicates that open clusters are a non-negligible formation channel. Specifically, the double pulsar J0737$-$3039 shows a $13.9\%$ ($5.4\%$) probability of originating from the young cluster OC 0450 (Theia 58). Based on encounter proximity and time, we argue that Theia 58 is its more plausible birthplace. Our work provides kinematic evidence consistent with an open-cluster origin for a subset of field BNSs.

Kinematic Evidence for Open Cluster Origins of Galactic Binary Neutron Stars

Abstract

We investigate the potential birthplace of Galactic binary neutron star (BNS) systems through a kinematic analysis. Using high-precision astrometry from Gaia DR3, updated pulsar distances, and Monte Carlo sampling of astrometric errors, we integrate the past trajectories of 11 Galactic BNSs and 167 globular clusters plus 2967 open clusters, to search for past encounters. Our results suggest that BNS origin in globular clusters is unlikely, with low encounter probabilities (e.g., for NGC 5139) and requiring excessive ejection velocities. Conversely, our analysis indicates that open clusters are a non-negligible formation channel. Specifically, the double pulsar J07373039 shows a () probability of originating from the young cluster OC 0450 (Theia 58). Based on encounter proximity and time, we argue that Theia 58 is its more plausible birthplace. Our work provides kinematic evidence consistent with an open-cluster origin for a subset of field BNSs.
Paper Structure (15 sections, 1 equation, 2 figures, 6 tables)

This paper contains 15 sections, 1 equation, 2 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Data and Methods
  3. Observations of Galactic BNS systems
  4. Catalogs of Galactic star clusters
  5. Orbit Integration and Encounter Analysis
  6. Results
  7. Assessing a Globular Cluster Origin
  8. Evidence for an Open Cluster Origin
  9. The Double Pulsar: A Case Study in Open Cluster Formation
  10. Conclusions
  11. Calibrating Candidate Associations with a Monte Carlo Null Test
  12. Any-cluster encounter probability $P_{\rm any}$
  13. Null hypothesis: speed-preserving isotropic velocity scrambling
  14. Pairwise excess above the null: enhancement ratio $R$
  15. Interpretation and scope

Figures (2)

  • Figure 1: Distributions of encounter lookback time ($\tau$) and ejection parameters for the pair J0737$–$3039 and Theia 58, as listed in Table \ref{['table4:encounter parameters']}.
  • Figure 2: Past trajectories of the double pulsar J0737–3039 (red line) and its two candidate birth open clusters, OC 0450 (blue line and green points for member stars) and Theia 58 (black line and magenta points for member stars). The dashed grey circle marks the $3r_{50}$ boundary of Theia 58. The assumed present BNS radial velocity is 66.25 km/s. The trajectories intersect Theia 58 at 7.43 Myr and OC 0450 at 8.04 Myr lookback time.