The radio waves we see from pulsars have a mysterious glitch – but now we know the ingredients that must be present in the heart of these ultra-dense stellar corpses to give their emissions a hiccup.
About 60 years ago, researchers noticed that the radio emissions from pulsars can suddenly and unexpectedly change in frequency, indicating that the pulsar’s rotation slowed down.
Pulsars are like nested shells of exotic quantum states of matter – they contain a layer of superconducting protons and another made of a superfluid of neutrons – housed within a crust of electrons and ions. For decades, physicists have theorised that the glitches happen when groups of tiny vortices in the neutron superfluid move to another layer.
Advertisement
But simulating this process is like simulating weather on a whole planet starting with millimetre-sized disturbances in air, says at École Normale Supérieure in Paris. This is why physicists often approximate or leave out some variables – Brachet and his team wanted to avoid that.
They found that replicating realistic glitches required taking account of interactions between vortices in the neutron superfluid and structures called “flux tubes” in the proton superconductor. Flux tubes are cylindrical structures filled with a magnetic field, and they slow down the vortices that cause the glitch.
Though their computer simulations only included a few dozen vortices, the results agreed with observations of real pulsars, implying that the team identified just the right ingredients you need to cook up a pulsar glitch.
“It is very gratifying how close we get to what has been observed,” says team member at the Indian Institute of Science.
at Louisiana State University says that the number of vortices on the move within a pulsar is typically around 10 trillion and they do so in groups, which then make other vortices move, forming a cascade. Computer simulations like this new one are helpful, but they still don’t account for every detail of every vortex’s motion, he says.
The researchers are now hoping to make their simulations bigger and investigate other mysterious phenomena, such as unexpected changes in a pulsar’s magnetic properties, says team member at the Indian Institute of Science.
arXiv
