A millisecond pulsar in a stellar triple system

Abstract: Gravitationally bound three-body systems have been studied for hundreds of years and are common in our Galaxy. They show complex orbital interactions, which can constrain the compositions, masses, and interior structures of the bodies and test theories of gravity, if sufficiently precise measurements are available. A triple system containing a radio pulsar could provide such measurements, but the only previously known such system, B1620-26 (with a millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of several decades), shows only weak interactions. Here we report precision timing and multi-wavelength observations of PSR J0337+1715, a millisecond pulsar in a hierarchical triple system with two other stars. Strong gravitational interactions are apparent and provide the masses of the pulsar (1.4378(13) Msun, where Msun is the solar mass and the parentheses contain the uncertainty in the final decimal places) and the two white dwarf companions (0.19751(15) Msun and 0.4101(3) Msun), as well as the inclinations of the orbits (both approximately 39.2 degrees). The unexpectedly coplanar and nearly circular orbits indicate a complex and exotic evolutionary past that differs from those of known stellar systems. The gravitational field of the outer white dwarf strongly accelerates the inner binary containing the neutron star, and the system will thus provide an ideal laboratory in which to test the strong equivalence principle of general relativity.

• The paper reveals the discovery of PSR J0337+1715, a millisecond pulsar in a gravitationally bound triple star system using high-precision timing observations.
• The study employs multi-wavelength analyses and numerical integration to precisely measure system parameters such as masses, spin period, and orbital inclinations.
• The research provides a unique laboratory for testing the strong equivalence principle and refining models of stellar evolution and gravitational interactions.

A Millisecond Pulsar in a Stellar Triple System

The discovery of PSR J0337+1715, a millisecond pulsar (MSP) in a gravitationally bound triple star system, provides an exceptional opportunity to investigate stellar evolution dynamics and test fundamental physics such as the strong equivalence principle (SEP) of general relativity. This research paper delineates the precision timing observations and multi-wavelength analyses that have led to this discovery, with significant implications for our understanding of both astrophysics and gravitational theory.

System Composition and Observations

PSR J0337+1715 is part of a hierarchical triple system consisting of a neutron star and two white dwarf (WD) companions. The MSP has a spin period of 2.73 milliseconds and was discovered as part of a pulsar survey conducted with the Green Bank Telescope (GBT). Following its initial identification as a binary with a 1.6-day circular orbit, anomalies in timing data suggested the presence of a third massive body. The combined radio timing observations from GBT, Arecibo, and Westerbork Synthesis Radio Telescope (WSRT) enabled high-precision measurements of the system's dynamics.

The analysis of this timing data, characterized by arrival time uncertainties as precise as 0.8 microseconds over 10 seconds, allowed for the determination of several key parameters:

• Mass of the pulsar: 1.4378(13) solar masses
• Masses of the white dwarf companions: 0.19751(15) solar masses and 0.4101(3) solar masses
• Inclinations of the orbits: approximately 39.2 degrees

These measurements were achieved by modeling the system dynamics through direct numerical integration, accounting for the significant three-body interactions present.

Implications for Gravity and Stellar Evolution

The PSR J0337+1715 system exhibits strong gravitational interactions, unlike any other previously known stellar triple systems with pulsars. The coplanar and nearly circular orbits of the system suggest a unique evolutionary past, including complex angular momentum interactions and mass transfer phases. The ability to measure such precise system parameters without reliance on traditional gravitational models places new constraints on our understanding of stellar evolution and binary formation theories.

Most notably, the system provides an unprecedented laboratory for testing the strong equivalence principle. In essence, it offers a rare test case where the differing gravitational binding energies of the neutron star and its less massive white dwarf companion result in stark contrasts. Considering the external gravity from the more massive WD, this can potentially amplify any SEP violation effects beyond what is possible using the Solar System tests or isolated binary systems.

Conclusion and Future Directions

The PSR J0337+1715 discovery brings unprecedented clarity to the dynamics of hierarchical triple systems, allowing for evolutionary narratives that include all phases from supernova events to mass accretion periods. Future long-term observations will enhance our understanding of potential secular changes in orbital parameters, furthering the analysis of the system's stability and the applicability of general relativity under strong gravitational interactions.

The expected continued high-precision timing of this system could refine constraints on SEP violations and other aspects of gravitational theory, contributing significantly to the broader understanding of astrophysical phenomena. The research around PSR J0337+1715 lays the groundwork for future explorations into the intricate ballet of celestial mechanics in complex systems.