Are Pulsar Glitches Triggered by a Superfluid Two-Stream Instability?

Mature neutron stars are expected to have several superfluid components. Strong evidence for this is provided by the glitches that have been observed in dozens of pulsars. We describe a superfluid analog of the two-stream instability that is well known in plasma physics and provide arguments that this instability is likely to be relevant for neutron stars. This is a new physical mechanism which may play a key role in explaining the glitch mechanism and which could also prove to be relevant in laboratory experiments on various superfluid systems.

Figure 1

The two-stream instability region for the case when the superfluid neutrons lag behind the superconducting protons in such a way that $\Delta \Omega /{\Omega }_{\mathrm{p}}=5\times {10}^{-4}$ ($\Lambda =1.0005$). The results are for $l=100$, which means that the unstable modes correspond to oscillations on a length scale of hundreds of meters. Similar instability regions exist for all $l>65$. Since typical values for a neutron star core are likely to be such that $x_{\mathrm{p}}<0.15$ and $0.4\le \epsilon \le 0.7$ one would expect the instability to operate in astrophysical neutron stars.