Colloquium: What can the spider web tell us ? A new pulsar story

© Guillaume Voisin

Spiders are a recently defined class of millisecond pulsars in binary systems: the so-called black widows feature a very low-mass stellar companion (typically Mc <0.05 Msol), and the so-called redbacks feature a low mass companion ( 0.1Msol < Mc < 0.5 Msol typically). In both cases, the companion orbits the pulsar very closely, with periods of a few hours only.

This promiscuity means that the companion is strongly affected by the pulsar: tidal effects, irradiation, and even evaporation. The bright side is, quite literally, that all these effects result in various observables that shine a light on parameters describing orbital properties (mass ratio, inclination...), or the pulsar wind composition and energetics. However, this comes at the cost of increased complexity and systematic uncertainty as one needs to model and calibrate the response of the companion star to these gravitational and radiative excitations by the pulsar.

Conversely, this opens new windows to probe the stellar physics of the companion, constrain the yet unclear evolution of these systems, and perhaps elucidate their connection to x-ray binaries and isolated millisecond pulsar formation.

In this talk, we will explore these different questions through a subjective selection of examples and recent modelling results concerning both the timing of these pulsars and the their companion's light curves. The image represents the modelled surface temperature map of the redback companion of PSR J2215+5135 (www.doi.org/10.1093/mnras/staa2876).