‘The Crab’

Part of the Springer Praxis Books book series (PRAXIS)


The discovery of the Crab and Vela pulsars put astronomers on the right track in deciding what pulsars were. The Crab pulsar, however, was to play an even more important role in pulsar astronomy. Aside from the intrinsic scientific interest of this object, it lies at the center of two stories of scientific priority. Priority — who discovered something first — is a big issue in science. Major discoveries always rely on technology (and hence technologists) and generally follow on from the work of others. Yet the fact remains that the scientist who gets their work into print earliest is given the credit for the discovery. An important and recurring factor in all this is not only making the right observations at the right time, but recognizing what you’ve seen. There are many examples of this in the story of pulsars, and perhaps none is more dramatic than the discovery of pulsars themselves. While Bell and Hewish have properly gone down in history as the discoverers of pulsars, pulsars were first detected, but not recognized, much earlier. Using an X-ray telescope, American astronomers had detected the pulsating signal from the Crab Nebula months prior to Hewish and Bell’s discovery; the trouble was, no one expected to find pulses in the observations and so, at least at first, no one thought to look. We’ll return to that story later, but first it is worthwhile to take a closer look at the discovery of the Crab pulsar, a discovery that unfolded in two episodes.


Neutron Star Radio Source Radio Telescope Radio Pulsar Supernova Remnant 
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  1. 1.
    A more detailed explanation of dispersion will be given in Chapter 8: The Searchers.Google Scholar
  2. 2.
    The telescope collapsed at 9:43pm EST on Tuesday the 15th of November 1988. (See Scholar
  3. 3.
    In fact even though most astronomers were confident in Baade and Minkowski’s prediction of a specific star in the middle of the Crab Nebula, it would be months before the star responsible for the pulses was positively identified using optical telescopes. This is the subject of the next chapter.Google Scholar
  4. 4.
    Later studies of the Crab pulsar explained why Staelin and Reifenstein were successful. The Crab occasionally emits pulses of enormous strength separated by much weaker periods of emission lasting seconds or more, now known as the ‘giant pulse’ phenomenon. Because of their rare character and random appearance, these giant pulses are difficult to identify. Repetitive dispersion was their revealing signature in this case.Google Scholar
  5. 5.
    The dish consists of almost 40,000 perforated aluminum panels, each 1 meter by 2 meters, which were added not long after the Crab pulsar observations described here. The new surface improved operation of the telescope at shorter wavelengths.Google Scholar
  6. 6.
    As we have seen, the possibility of a confirmed SETI signal was a controversial and irritating factor in the delay in the announcement of the original pulsar discovery.Google Scholar
  7. 7.
    Unlike the land in the Middle East, the name of this town is pronounced ‘Palesteen’.Google Scholar
  8. 8.
    γ-rays (pronounced gamma rays) and X-rays are short wavelength, high energy form of radiation, part of the same spectrum as light and the longer wavelength radio waves.Google Scholar
  9. 9.
    This was said during an interview on a TV program ‘NOVA’ on supernovae about twenty years ago.Google Scholar

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© Praxis Publishing Ltd. 2008

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