Pulsars: Structure and Dynamics

As is so often the case either the poet has an insight so far denied to the rest of us or his theory of pulsars is quite muddled. A great deal now seems under­ stood about these delightful surprising objects-except for details of how they pulse. But there are already so many clues from pulsar observations that one cannot be optimistic that continued observations of the periodic radio signals will offer crucial new evidence. In the two years since the review of Hewish (1970) the number of observed pulsars has increased modestly from 50 to 58 (November 1971), accompanied by a plethora of over three hundred theoretical papers. There have been.no novel revelations: The rotating neutron star still has no serious competitor as the pulsar clock; its spin is almost certainly coupled to its environment by a huge magnetic field for which a consensus of estimates gives a value at the stellar surface of order 1012 G; the observed variations in radio in­ tensity (and also in optical, X-ray, and ')I-ray fluxes for the pulsar in the Crab nebula) are usually assumed to be associated with nonalignment of the stellar dipole magnetic field and spin axis. Some kind of coherent emission process is necessary to account for the enormous radio intensities of pulsars. All of these entrenched ideas have become even more established. There have been activity and progress in the following areas: (1) The rich variety of pulse shapes, polarizations, and intensity variations have been further confirmed and explored. In a given pulsar there can be marked correlation over many pulses as well as remarkable differences. The main problem now is deciding which among the numerous data are fundamental and how many of them a tentative theory must fit. (2) An enormous amount of detail about the Crab pulsar (NP 0532) radia­ tion is now available: radio, optical, X-ray and ')I-ray pulses, their structure, and correlations between pulses in different regimes. Changes in the surrounding nebula have been described that may be associated with pulsar variations. Very precise timing measurements before and after period discontinuities (glitches)