The so-called ``lighthouse model'' used to explain the basic
pulsar phenomenon is demonstrated in the animated image shown in
Fig.
1
. As the neutron star spins, charged particles are accelerated
out along magnetic field lines in the magnetosphere (depicted by
the light blue cones). This acceleration causes the particles to
emit electromagnetic radiation, most readily detected at radio
frequencies as a sequence of observed pulses produced as the
magnetic axis (and hence the radiation beam) crosses the
observer's line of sight each rotation. The period of the pulses
is simply the rotation period of the neutron star. The position
of the tracker ball on the idealised pulse profile in the
animation shows precisely the relationship between observed
intensity and rotational phase of the neutron star.
Figure 1:
The rotating neutron star (or ``lighthouse'') model for pulsar
emission. Click here to see the movie in action. Animation
designed by Michael Kramer.
Neutron stars are extremely stable rotators. They are
essentially equivalent to large celestial flywheels with moments
of inertia
. The rotating neutron star model, which was independently
developed by Pacini and Gold in 1968 [121,
65] correctly predicts that the pulse period should gradually
increase as the outgoing radiation carries away rotational
kinetic energy. When a period increase of 36.5 ns per day was
measured for the pulsar in the Crab nebula [130], Gold showed that a rotating neutron star with a large magnetic
field must be the dominant energy supply to the nebula and the
model became universally accepted.
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Binary and Millisecond Pulsars
D. R. Lorimer (dunc@mpifr-bonn.mpg.de)
http://www.livingreviews.org/lrr-1998-10
© Max-Planck-Gesellschaft. ISSN 1433-8351
Problems/Comments to
livrev@aei-potsdam.mpg.de
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