# Dark neutron stars

## TL;DR

This paper explores the conditions under which dark neutron stars, lacking observable gamma-ray emissions, could exist due to the absence of pair creation in their magnetospheres, and discusses their potential observational signatures.

## Contribution

It introduces the concept of dark neutron stars as radio-quiet objects with no gamma-ray emissions, based on pair creation processes and magnetospheric charge conditions.

## Key findings

- Few Fermi LAT pulsars have significant outer-gap pair creation.
- Dark neutron stars are likely radio-quiet and gamma-ray silent.
- The absence of pair creation influences the star's emission properties.

## Abstract

There is good evidence that electron-positron pair formation is not present in that section of the pulsar open magnetosphere which is the source of coherent radio emission, but the possibility of two-photon pair creation in an outer gap remains. Calculation of transition rates for this process based on measured whole-surface temperatures, combined with a survey of gamma-ray, X-ray and optical luminosities, expressed per primary beam lepton, shows that few Fermi LAT pulsars have significant outer-gap pair creation. For radio-loud pulsars with positive polar-cap corotational charge density and an ion-proton plasma there must be an outward flow of electrons from some other part of the magnetosphere to maintain a constant net charge on the star. In the absence of pair creation, it is likely that this current is the source of GeV gamma-emission observed by the Fermi LAT and its origin is in the region of the outer gap. With negative polar-cap corotational charge density, the compensating current in the absence of pair creation can consist only of ion or protons. These neutron stars are likely to be radio-quiet, have no observable gamma-emission, and hence can be described as dark neutron stars.