Why are pulsar planets rare?

TL;DR

The paper explains the rarity of pulsar planets by identifying two key factors: the need for a specific companion star destruction process and the low likelihood of dead zones in pulsar disks due to irradiation effects.

Contribution

It proposes a new explanation for the scarcity of pulsar planets based on formation conditions involving companion star destruction and disk irradiation effects.

Findings

Formation requires destruction of a suitable companion star.

Irradiation prevents dead zone formation in pulsar disks.

Rarity explained by low probability of both conditions being met.

Abstract

Pulsar timing observations have revealed planets around only a few pulsars. We suggest that the rarity of these planets is due mainly to two effects. First, we show that the most likely formation mechanism requires the destruction of a companion star. Only pulsars with a suitable companion (with an extreme mass ratio) are able to form planets. Second, while a dead zone (a region of low turbulence) in the disk is generally thought to be essential for planet formation, it is most probably rare in disks around pulsars because of the irradiation from the pulsar. The irradiation strongly heats the inner parts of the disk pushing the inner boundary of the dead zone out. We suggest that the rarity of pulsar planets can be explained by the low probability for these two requirements - a very low-mass companion and a dead zone - to be satisfied.