Pulsars



Pulsars. There is still much for astronomers to learn about pulsars. Based on what is known the term pulsar is used to describe the phenomenon of short, precisely timed radio bursts that are emitted from somewhere in space. Though all is not known about pulsars, they are now believed in reality to emanate from spinning neutron stars, highly reduced cores of collapsed stars that are theorized to exist. Pulsars were discovered in 1967, when Jocelyn Bell, a graduate student at Cambridge University, noticed an unusual pattern on a chart from a radio telescope. What made this pattern unusual was that, unlike other radio signals from celestial objects, this series of pulses had a highly regular period of 1.33730119 seconds. Because day after day the pulses came from the same place among the stars, Cambridge researchers came to the conclusion that they could not have come from a local source such as an Earth satellite. A name was needed for this newly discovered phenomenon. The possibility that the signals were coming from a distant civilization was considered, and at that point the idea of naming the phenomenon L.G.M. (short for Little Green Men) was raised. However, after researchers had found three more regularly pulsing objects in other parts of the sky over the next few weeks, the name pulsar was selected instead of L.G.M. This name was selected because it indicates a regularly pulsing radio source. As more and more pulsars were found, astronomers engaged in debates over their nature. It was determined that a pulsar could not be a star inasmuch as a normal star is too big to pulse so fast. The question was also raised as to whether a pulsar might be a white dwarf star, a dying star that has collapsed to approximately the size of the Earth and is slowly cooling off. However, this idea was also rejected because the fastest pulsar known at the time pulsed around thirty times per second and a white dwarf, which is the smallest known type of star, would not hold together if it were to spin that fast. The final conclusion among astronomers was that only a neutron star, which is theorized to be the remaining core of a collapsed star that has been reduced to a highly dense radius of only around 10 kilometers, was small enough to be a pulsar. Further evidence of the link between pulsars and neutron stars was found in 1968, when a pulsar was found in the middle of the Crab Nebula. The Crab Nebula is what remains of the supernova of the year 1054, and inasmuch as it has been theorized that neutron stars sometimes remain following supernova explosions, it is believed that the pulsar coming from the Crab Nebula is evidently just such a neutron star. The generally accepted theory for pulsars is the lighthouse theory, which is based upon a consideration of the theoretical properties of neutron stars and the observed properties of pulsars. According to the lighthouse theory, a spinning neutron star emits beams of radiation that sweep through the sky, and when one of the beams passes over the Earth, it is detectable on Earth. It is known as the lighthouse theory because the emissions from neutron stars are similar the pulses of light emitted from lighthouses as they sweep over the ocean; the name lighthouse is therefore actually more appropriate than the name pulsar. The periodic flashing of pulsars is related to rotation rather than pulsing, so the name pulsar is actually not very accurate.