2.1 The lighthouse model
Figure 2 shows an animation depicting the rotating neutron star, also known as the “lighthouse” model.
As the neutron star spins, charged particles are accelerated along magnetic field lines forming a beam
(depicted by the gold cones). The accelerating particles emit electromagnetic radiation, most readily
detected at radio frequencies as a sequence of observed pulses. Each pulse is produced as the magnetic axis
(and hence the radiation beam) crosses the observer’s line of sight each rotation. The repetition period of
the pulses is therefore simply the rotation period of the neutron star. The moving “tracker ball” on the
pulse profile in the animation shows the relationship between observed intensity and rotational phase of the
Figure 2: GIF movie showing the rotating neutron star (or “lighthouse”) model for pulsar emission.
Animation designed by Michael Kramer.
Neutron stars are essentially large celestial flywheels with moments of inertia 1038 kg m2. The
rotating neutron star model [279, 127] predicts a gradual slowdown and hence an increase in
the pulse period as the outgoing radiation carries away rotational kinetic energy. This idea
gained strong support when a period increase of 36.5 ns per day was measured for the pulsar
in the Crab nebula , which implied that a rotating neutron star with a large magnetic field must be
the dominant energy supply for the nebula .