Orbital Parameters of Binary Radio Pulsars : Revealing Their Structure, Formation, Evolution and Dynamic History

Abstract

Orbital parameters of binary radio pulsars reveal the history of the pulsars' formation and evolution including dynamic interactions with other objects. Advanced technology has enabled us to determine these orbital parameters accurately in most of the cases. Determination of post-Keplerian parameters of double neutron star binaries (especially of the double pulsar system PSR J0737-3039) provide clean tests of the general theory of relativity and in the future may lead us to constrain the dense matter Equations of State. For binary pulsars with main-sequence or white dwarf companions, knowledge about the values of the orbital parameters as well as of the spin periods and the masses of the pulsars and the companions might be useful to understand the evolutionary history of the systems. As accreting neutron star binaries lead to orbit circularization due to the tidal coupling during the accretion phase, their descendants i.e. binary millisecond pulsars are expected to be in circular orbits. On the other hand, dense stellar environments inside globular clusters cause different types of interactions of single stars with pulsar binaries like "fly-by", "exchange", and "merger". All these interactions impart high eccentricities to the pulsar binaries. So it is quite common to get eccentric millisecond pulsar binaries in globular clusters and we find that "fly-by" causes intermediate values of eccentricities while "exchange" or "merger" causes high values of eccentricities. We also show that "ionization" is not much effective in the present stage of globular clusters. Even in the absence of such kinds of stellar interactions, a millisecond pulsar can have an eccentric orbit as a result of Kozai resonance if the pulsar binary is a member of a hierarchical triple system. PSR J1903+0327 is the only one eccentric millisecond pulsar binary in the galactic disk where stellar interactions are negligible. The possibility of this system to be a member of a hierarchical triple system or past association of a globular cluster have been studied and found to be less likely.