Special Astrophysics Seminar

Binary radio pulsars in globular clusters: their orbital eccentricities and interaction with other stars

Alak Ray

Tata Institute of Fundamental Research

Sustained high sensitivity searches of globular clusters (GC) for radio pulsars by improved pulsar search algorithms and pulsar timing experiments have yielded some 140 pulsars in more than two dozen GCs. The observed distribution of orbital eccentricity and period of binary radio pulsars in GCs have signatures which appear to be from the past imprint of the interaction between single pulsars and binary systems or of binary pulsars and single passing normal stars that includes exchange and merger of stars. It is seen that GCs have different groups of pulsars arising from separate interaction or evolutionary scenarios. We analyse these distributions using computational tools like the STARLAB software. The corresponding distribution for galactic field pulsars show notable difference from the GC pulsar orbital period and eccentricity distribution. The long orbital period pulsars in the galactic field with frozen out low eccentricities are missing in globular clusters and we show that ionization alone of these systems in GCs cannot account for the peculiarities. Some of the short orbital period systems will undergo merger due to gravitational wave radiation and will be a source of gamma-ray bursts if both stars are neutron stars in a binary.

I will also discuss the observable signatures associated with one of the proposed formation scenario for the highly eccentric binary millisecond pulsar PSR J1903+0327 in terms of a hierarchical triplet and argue that if it originated in a GC, then the set of such GCs will have to be somewhat restricted in their properties.