Binary and Millisecond Pulsars

Abstract: We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of 1.5 solar masses, a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric (e=0.44) orbit around an unevolved companion.

• The paper details extensive pulsar surveys that have expanded the known population to over 1800, including numerous binary and millisecond systems.
• It analyzes pulsar timing and rotational stability, showing that millisecond pulsars maintain exceptional precision with minimal period increases.
• The study leverages binary systems like the double pulsar J0737–3039 as natural laboratories for rigorous tests of general relativity and gravitational theories.

An Essay on "Binary and Millisecond Pulsars" by Duncan R. Lorimer

The paper "Binary and Millisecond Pulsars" offers a comprehensive examination of the properties, demographics, and applications of radio pulsars, particularly those in binary configurations or possessing millisecond periods. Pulsars are highly magnetized, rapidly rotating neutron stars formed during supernova explosions, and they present an intriguing array of astrophysical phenomena and applications.

Pulsar Demographics and Surveys

Recent pulsar surveys have drastically increased the known pulsar population beyond 1800, with 83 binary and millisecond pulsars detected within our Galaxy's disk, and 140 pulsars across 26 Galactic globular clusters. The paper highlights several developments, such as the discovery of the young relativistic binary system PSR J1906+0746, advancements in the study of globular cluster pulsars, and noteworthy mass measurements exceeding $1.5\,M_\odot$.

Observational Characteristics and Models

Pulsars exhibit pulse periods predominantly centered around 0.5 seconds, progressing at secular rates of $\dot{P} \sim 10^{-15} \mathrm{\ s/s}$. Millisecond pulsars, however, demonstrate much shorter periods (1.4 to 30 milliseconds) and minimal period increases ($\dot{P} \lesssim 10^{-19} \mathrm{\ s/s}$). Their rotational energy loss rates and magnetic field strengths delineate two distinct populations. The lighthouse model aptly conceptualizes pulsar emission, underlining the role of charged particle acceleration along magnetic field lines, radiating a rotating beam observable as electromagnetic pulses upon intersection with an observer’s line of sight.

Timing, Stability, and Binary Dynamics

In dissecting pulsar timing, the author underscores the necessity of transforming time-of-arrival (TOA) measurements into a framework that accounts for Earth's motion and other relativistic effects. The stability of pulsar rotations enables their utility for precision timing applications. Interestingly, despite general stability, phenomena such as timing noise are prevalent in younger pulsars, presumed to stem from interior superfluid dynamics or magnetospheric changes.

Binary pulsars, particularly in tight orbits, present opportunities to explore gravitational theories. The system J0737$-$3039 (the double pulsar) serves as a notable laboratory, permitting tests of general relativity (GR) via multiple post-Keplerian parameters. Confirmations of GR include extraordinarily precise measurements of relativistic periastron advance and redshift parameters, with results consistent within minimal error margins.

Implications and Future Directions

The empirical estimates and demographic analyses have profound implications for understanding the Galactic pulsar population. The projected population is significant, yet the birthrate of these systems indicates a substantial number remain to be discovered, particularly at lower luminosities or in regions with observational biases. Importantly, the prospects of detecting gravitational waves from pulsar binaries are enhanced with present and future observatories, which could soon provide novel insights into the Galactic binary population. Millisecond pulsars notably compile a sensitive array for detecting gravitational wave backgrounds, rivaling dedicated gravitational wave detectors in certain parameters.

Conclusion

In conclusion, this review paper succinctly captures the advancements and intricacies in the study of binary and millisecond pulsars, showcasing their invaluable role in probing fundamental physics. The paper serves as an essential guide for current researchers endeavoring to deepen our understanding of these celestial objects, leveraging pulsars' timing properties and binary dynamics to shed light on phenomena such as gravitational radiation and neutron star interior states. As observational capabilities progress, the field anticipates further groundbreaking discoveries and theoretical constraints that will continue to enrich astrophysics.