Small glitches: the role of strange nuggets?

Abstract

Pulsar glitches, i.e. the sudden spin-ups of pulsars, have been detected for most pulsars that we known. The mechanism giving rise to this kind of phenomenon is uncertain, although a large data set has been built. In the framework of star-quake model, based on~\cite{Baym1971}, the glitch-sizes (the relative increases of spin-frequencies during glitches) $\Delta \Omega/\Omega$ depend on the released energies during glitches, with less released energies corresponding to smaller glitch sizes. On the other hand, as one of dark matter candidates, our Galaxy might be filled with the so called strange nuggets (SNs) which are the relics from the early Universe. In this case the collisions between pulsars and SNs is inevitable, and these collisions would lead to glitches when enough elastic energy has been accumulated during the spin-down process. The SNs-triggered glitches could release less energy, because the accumulated elastic energy would be less than that in the scenario of glitches without SNs. Therefore, if a pulsar is hit frequently by SNs, it would tend to have more small size glitches, whose values of $\Delta \Omega/\Omega$ are smaller than that in standard star-quake model (with larger amounts of released energy). Based on the assumption that in our Galaxy the distribution of SNs is similar to that of dark matter, as well as on the glitch data in ATNF Pulsar Catalogue and Jodrell Bank glitch table, we find that in our Galaxy the incidences of small size glitches exhibit tendencies consistent with the collision rates of pulsars and strange nuggets. Further test of this scenario is expected by detecting more small glitches (e.g., by the Square Kilometre Array).