As Orion strides forward, bow in hand, he seems to confront the constellation Taurus, the bull. A small telescope will reveal, near the tip of the bull's southern horn, a faint patch of light. It is called the Crab Nebula, and in a large telescope, it appears to be an explosion in progress, as shown on page 9. If the Orion Nebula is a stellar nursery, then the Crab Nebula next door may be the grave site of a star that suffered a death of unimaginable violence. The Andromeda galaxy, the most distant object visible to the naked eye.
Astronomers call such a spectacular stellar suicide a supernova.
At the heart of the Crab Nebula lies one of the strangest objects in the known universe. According to scientists, the tiny corpse of a deceased star, compressed into unbelievable densities, spins in its grave 30 times per second, sending out a beam of radio waves that were first detected on earth in 1968. It is called a pulsar, described as a spinning supernova remnant so compressed that the electrons and protons in the atoms of the original star have been squeezed together to produce neutrons. Scientists say it was once the massive core of a supergiant star like Betelgeuse or Rigel in Orion. When the star exploded and the outer layers were blasted into space, only the shrunken core was left, a glowing white-hot cinder, its nuclear fires long extinguished.