Having established the existence of pulsars, the next natural questions were: how many are out there, and are they all the same? There are several reasons why astronomers want to know. For one thing, since pulsars are clearly an important aspect of the story of stellar evolution, astronomers wanted to know just how many supernovae spawn pulsars and how often? It was also known that the pulsars radiate away angular momentum causing them to slow down as they age. It followed that if you could determine the slow-down rate of a pulsar, it would be one indication of how old it is. There were other factors to be explored about pulsars, too, such as how much energy they gave off, and how stable the periods were over time. Also, pulsars are made of some pretty strange stuff so represented a way of exploring the behavior of high density matter. But the observation of pulsars isn’t confined to pulsars themselves; they also act as a probe of the interstellar medium. The radiation from a pulsar is subtly changed during its journey from the pulsar and Earth. Because the beam is so narrow and precise it passes through a long, thin sample of the intervening space. The features of this sample are imprinted on the beam when it arrives at Earth. For example, magnetism affects the way the beam is polarized and so by studying the polarization of pulsar beams in many directions astronomers can build up a three dimensional map of the magnetic Milky Way.
KeywordsRadio Source Radio Pulse Dispersion Measure Individual Pulse Finish Line
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