Page 34 - Curriculum Visions Dynamic Book

Pulsars (pulsating radio stars)
PUlsars emit very regular pulses of radio Waves. They are associated with neUtron stars.
When a neutron star forms during
a supernova phase, neUtrons on the outer edge of the stars change into protons and electrons, which have electrical charges. Because they are charged particles, they then get caught in the magnetic field surrounding the supernova and spin with it at speeds approaching that of light.
The only places where the particles
can escape the magnetic field are at the
magnetic poles, and that produces the
point sources of radio waves that we can
detect. The magnetic poles are not at the
same places as the geographic poles, and so they move with the rotation of the star. (To visualize this, think of the Earth’s north magnetic pole being at New York. As the Earth spins, the pole at New York faces out into different parts of space.)
Although the poles are continuously giving off radio waves, the waves are only sent in our direction when the spin of the star turns a pole to face us. This is similar to the way a lighthouse appears to be giving off flashing beams when in fact it is putting out a constant beam of light.
Pulsars have very short lives and may last no more than 10 million years, after which the magnetic fields are not strong enough to create the effect.
There is a pulsar in the Crab Nebula, which was probably formed at the same time as the supernova, about A.d.1054 (see page 33).
So far, over 300 pulsars are known that spin
 This picture shows a pulsar within the Crab Nebula, a rapidly rotating neutron star the size of Manhattan.
Bright wisps can be seen moving outward at half the speed of light to form an expanding ring that is visible in both X-ray and optical images.
Another dramatic feature is a turbulent jet that lies perpendicular to the inner and outer rings. It is a stream of matter moving at half the speed of light!
(See also pages 32–33.)
every 4 seconds or faster. One has been recorded spinning at 642 times per second. However, it is believed that there are one million active pulsars in the Milky Way Galaxy alone. To sustain this number, a pulsar, like its parent supernova, must be born every few decades.
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