The paper presents a self-consistent, semi-analytical model to explain the formation of the galactic millisecond pulsar triple system PSR J0337+1715. This system features an unusual configuration of a neutron star (NS) accompanied by two orbiting white dwarfs (WDs), posing challenges to established stellar evolution and interaction theories, specifically within close multiple stellar systems.
Summary of Findings
PSR J0337+1715 is a highly hierarchical system comprising a 1.438 solar mass (M☉) radio millisecond pulsar with a spin period of 2.73 milliseconds. It is orbited by two white dwarfs with masses of 0.197 M☉ and 0.410 M☉, and orbital periods of 1.63 days and 327 days, respectively. This configuration offers the first precise confirmation of the white dwarf mass and orbital period (M-WD-P-orb) relation in a wide orbit system. The paper details the evolutionary trajectory from the system's zero-age main sequence (ZAMS) stage to its current form.
Evolutionary Model
The authors use a semi-analytical approach to trace the system's evolution backward from its present-day configuration. The model suggests an initial ZAMS with a massive primary star of 10 M☉ and two lower-mass companions. The system undergoes several key evolutionary stages:
- Common Envelope (CE) Phase:
- The primary star undergoes a CE phase leading to significant orbital angular momentum loss, affecting both inner and outer orbits.
- The CE evolution results in a reduced orbital period for the inner system (2.47 days) and the tertiary star (17.1 days).
- Case BB Roche-Lobe Overflow (RLO) and Supernova (SN):
- Post-CE, the primary's helium core expands and undergoes Case BB RLO followed by an SN, resulting in a neutron star.
- The inner binary's post-SN configuration is crucial, as it affects the system's survival during the explosive event.
- Double Low-Mass X-Ray Binary (LMXB) Phases:
- Subsequent LMXB phases are responsible for the formation of the two white dwarfs, with mass loss occurring at significantly non-conservative rates.
- The inner binary experiences extended mass transfer, effectively recycling the pulsar.
Implications and Observational Corroboration
The existence of the PSR J0337+1715 system in the galactic field provides new insights into CE evolution in hierarchical triples, especially regarding angular momentum loss and in-spiral dynamics. Theoretical constraints such as the stability of hierarchical structures and M-WD-P-orb relations are well-matched with observational data, providing strong evidence for the proposed evolutionary model.
Future Research Directions
Further extension of the model toward inclusion of population synthesis to evaluate the likelihood of various evolutionary paths could yield deeper understanding. Additionally, direct dynamical simulations of CE interactions in triple systems and examination of other possible evolutionary scenarios, such as quadruple origins or cluster formation and ejection, may be worthwhile avenues for exploration.
Overall, the research at hand advances the understanding of stellar evolution dynamics in complex systems and underscores the importance of observational precision in confirming theoretical predictions.