A Pulsar’s Inner Secrets

Physics 5, s189
Glitches in the rotation of pulsars cannot be explained by the conventional model of superfluid neutrons beneath the star’s crust.

Pulsars are neutron stars that sweep space with beams of radiation much like lighthouses: the periodicity of the pulsar allows us to track the star over its life cycle, as well as nearby gravitational bodies. Gradually, a pulsar spins down as it loses energy, but young pulsars exhibit glitches, in which the rotation rate increases suddenly. The current explanation for the glitches is that the neutron star’s crust contains a neutron superfluid that resists the spin-down effect: when vortices break free from the nuclear lattice and transfer angular momentum to the crust, the pulsar is seen to rotate faster.

Nils Andersson at the University of Southampton, UK, and colleagues, now point out in a paper in Physical Review Letters that this model has a few glitches of its own. Combining the most recent glitch data and a model of the superfluid that takes into account relativistic effects, the authors find that the amount of superfluid in the crust cannot explain the changes in angular momentum required to account for the glitches. In other words, additional contributions to the moment of inertia must be coming from somewhere, most likely the superfluid in the core.

An important ingredient in all of this is the effective neutron mass in the superfluid, which, as pointed out in an earlier paper in Physical Review C by Nicholas Chamel of the Université Libre de Bruxelles, might be very large. Indeed, Chamel considers the implications for pulsar glitches in an independent paper now published in Physical Review Letters, and arrives at similar conclusions: the crust superfluid is not enough to explain the data. – David Voss

Subject Areas


Related Articles

Black Hole Area Law Tested

Black Hole Area Law Tested

By comparing the sizes of black holes before and after a merger, researchers have tested Hawking’s theorem on black hole areas. Read More »

Pulsar Halo Hints at Slow Diffusion of Cosmic Rays  
Particles and Fields

Pulsar Halo Hints at Slow Diffusion of Cosmic Rays  

Observations made by the LHAASO gamma-ray observatory show huge differences in the rate at which charged particles propagate through the Milky Way. Read More »

Experiment Casts Doubt on Potential Dark Matter Find

Experiment Casts Doubt on Potential Dark Matter Find

The DAMA/LIBRA experiment’s potential dark matter detection went unconfirmed for 20 years. Now, a similar experiment offers evidence against the result. Read More »

More Articles