On the nature and evolution of the unique binary pulsar J1903+0327

Abstract: (abridged) PSR J1903+0327, a millisecond pulsar in an eccentric (e = 0.44) 95-day orbit with a (~ 1Msun) companion poses a challenge to our understanding of stellar evolution in binary and multiple-star systems. Here we describe optical and radio observations which rule out most of the scenarios proposed to explain formation of this system. Radio timing measurements of three post-Keplerian effects yield the most precise measurement of the mass of a millisecond pulsar to date: 1.667 +/- 0.021 solar masses (99.7% confidence limit) (...). Optical spectroscopy of a proposed main sequence counterpart show that its orbital motion mirrors the pulsar's 95-day orbit; being therefore its binary companion (...) The optical detection also provides a measurement of the systemic radial velocity of the binary; this and the proper motion measured from pulsar timing allow the determination of the systemic 3-D velocity in the Galaxy. We find that the system is always within 270 pc of the plane of the Galaxy, but always more than 3 kpc away from the Galactic centre. Thus an exchange interaction in a dense stellar environment (like a globular cluster or the Galactic centre) is not likely to be the origin of this system. We suggest that after the supernova that formed it, the neutron star was in a tight orbit with a main-sequence star, the present companion was a tertiary farther out. The neutron star then accreted matter from its evolving inner MS companion, forming a millisecond pulsar. The former donor star then disappears, either due to a chaotic 3-body interaction with the outer star (caused by the expansion of the inner orbit that necessarily results from mass transfer), or in the case of a very compact inner system, due to ablation/accretion by the newly formed millisecond pulsar.

• The paper refines the pulsar’s mass measurement (1.667 ± 0.021 solar masses) and spin-up processes through combined optical and radio observations.
• It identifies an unusually eccentric orbit (e = 0.44) around a 1 solar mass main-sequence companion, challenging classical binary evolution scenarios.
• The study proposes a triple system origin as an alternative formation mechanism, urging further simulations of complex stellar interactions.

Analyzing the Unique Properties and Formation of Binary Pulsar PSR J1903+0327

This paper presents a comprehensive analysis of the binary millisecond pulsar PSR J1903+0327, a system whose properties significantly challenge traditional models of stellar evolution, particularly within binary and multiple-star systems. Through a combination of optical and radio observations, the study refines our understanding of the pulsar and its companion's characteristics and offers insights into the mechanisms that may have led to its unusual formation.

The sheer uniqueness of PSR J1903+0327 becomes evident with its eccentric orbit (e = 0.44) around a 1 solar mass companion, starkly contrasting the expected circular orbits in classical binary evolution scenarios post-recycling phase. The precise measurement of the pulsar's mass, determined to be 1.667 ± 0.021 solar masses, constitutes a critical outcome of the study, pushing the boundaries of acceptable equations of state for super-dense matter and corroborating theories of pulsar spin-up via mass accretion, indicated by its rotational properties and magnetic field measurements.

Optical spectroscopy confirms that the pulsar's companion mirrors the 95-day orbital motion, dispelling prior suppositions of a hierarchical triple system and establishing the companion as a main-sequence star. This finding refutes the conventional binary MSP evolution model and suggests that the current companion was not the donation source of mass responsible for the pulsar's short spin period and low magnetic field.

The implications of the study stretch beyond mere characterization. The synthesized radar timing and optical data, which determine the 3D velocity within the Galaxy, highlight that PSR J1903+0327 has a modest peculiar velocity and a constant distance to the Galactic plane, weakening hypotheses of its origination from a dense stellar environment like a globular cluster, where exchange interactions are conceivable.

The proposal of a triple system origin, where a former inner binary component was ejected, stands out as a plausible explanation for PSR J1903+0327's formation. This theory accounts for the present eccentricity and distance variations without invoking traditional dense stellar environment interactions. Future modeling and simulations are encouraged to explore these triple-system formation scenarios exhaustively, providing deeper insights into massive star evolution and the physics governing neutron star masses and rotational behaviors.

In conclusion, the paper posits critical insights into pulsar astrophysics, utilizing an interdisciplinary approach to address fundamental questions about peculiar binary systems. This research will likely influence theoretical and observational perspectives on thermal and structural properties of dense matter and the lifecycle evolution of neutron stars in complex stellar systems.