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A pulsar is a highly magnetized rotating neutron star that emits a beam of electromagnetic radiation. The beam of emission is only possible to be observed when it is pointing towards the Earth. The principle is similar to a lighthouse. The beam of light can only be observed when it is pointing in the direction of the observer. Neutron stars are very dense, and have short, regular rotational periods. This produces a precise interval between pulses that range from milliseconds to seconds for an individual pulsar. The longest known pulsar period is 9.437 seconds. The periods of pulsars make them useful tools. The observations of a pulsar in a binary neutron star system are used indirectly to confirm the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar. Certain types of pulsars also rival atomic clocks in their ability and accuracy in keeping time. Pulsars formulate when a core of a massive star is compressed during a supernova. The core collapses into a neutron star. The neutron star will retain most of its angular momentum although its moment of inertia is reduced. Therefore it will form at very high rotational speed. A beam of radiation is emitted along the magnetic axis of the pulsar which will spin along the rotation of the neutron star. The magnetic axis of the pulsar will determine the direction of the electromagnetic beam. However the magnetic axis is not necessarily the same as the rotational axis. This misalignment of the axis cause the beam to be seen once every rotation and therefor lead to a “pulsed” nature of the pulsars.

Why a Star of Mass 0.5M Collapses

i) Briefly explain why a star of mass 0.5A/1,, collapses to form a white dwarf when the nuclear reactions in its core cease. (ii) That is the maximum theoretical mass of a white dwarf? Describe (in about 100 words) what happens to a star if its mass exceeds this value. (iii) What is the maximum theoretical mass of a neut