What the Pulsars Tell Us

Neutron stars don't stand still. Just like the stars of which they are a remnant, they rotate. Since they have collapsed from a much larger size, they spin rapidly. Recall from Chapter 12, "Solar System Family Snapshot," the discussion of conservation of angular momentum: A rotating body (like a whirling skater drawing in her arms) spins faster as it shrinks. A neutron star has shrunk from a body hundreds of times larger than the sun to one that is smaller than the Earth. The earth takes 24 hours to make one revolution. A very massive but very small neutron star does it in a fraction of a second.

The rate of rotation is not the only property that intensifies in the neutron star. Its magnetic field is many times stronger than that of the parent star because the lines of the magnetic field are compressed along with the matter of the core itself. The combination of rapid rotation and a powerful magnetic field serves to announce the presence of some neutron stars in the universe.

In the late 1960s, S. Jocelyn Bell Burnell was a graduate student at Cambridge University working with Anthony Hewish, looking for interesting sources of radio emission. One very strange signal was detected: an an instantaneous burst of emission followed by a brief pause, and then another pulse. The pulses and pauses alternated with great precision—as it turns out, with a precision greater than that of the most advanced and accurate timepieces in the world.

In 1974, Hewish received the Nobel Prize in Physics for the discovery of the radio signals now called pulsars.

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