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- Pulsars are super dense Neutron Stars. They are the remnants of a massive star that has exploded as a supernova. A Neutron Star will have more that one Solar Mass of weight compressed into a volume the size of city of San Francisco. A larger mass star compressed to greater density would collapse into a Blackhole.
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- Pulsars are Neutron Stars that emit radio waves and probably other wavelengths in the electromagnetic spectrum. The radio waves in particular are detected as pulses. The waves are emitted out of the magnetic poles of a rotating star. Because the magnetic poles do not precisely line up with the rotational poles the rotating beam circles like a lighthouse beam. When the beam crosses the Earth’s line of sight our telescopes detect a pulse of radio waves.
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- Astronomers can precisely measure the timing of these pulses. The precision of the pulses is better than our best atomic clocks.
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- Gravity is the most fundamental force in nature. For eons man has been trying to understand what really creates gravity. Is it a force or a warping of space-time, a geometry. Is it the same force ever where in the Universe. Does it always fall off as the inverse square of the distance? Or, is it always constant regardless of the size of the mass. Does it work at the quantum level of atoms? There are many theories today after the truth. Pulsars are precision instruments that may help astronomers better understand the force of gravity, or not.
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- Pulsar’s motions have been observed to learn if gravity behaves differently around Neutron Stars. To date no differences have been found to indicate that the Pulsar’s motion depends on the star’s internal structure. Precise measurements of Pulsars will allow astronomers to put constraints on these internal physics of Neutron Stars
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- Under Einstein’s Theory of General Relativity the prediction is made that the motions of masses cause disturbances in the space-time geometry resulting in the emission of gravitational waves. Emitting gravity waves would remove energy from the system. Energy must be conserved, so, there must be an equivalent loss of energy somewhere else in the system that can be detected.
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- Gravity waves themselves have yet to be detected. However, we have indirect evidence that they exist. Astronomers studying Pulsars in binary systems have been found them to decay in their orbits and to eventually spiral into each other causing a supernova explosion. Somehow the system is loosing rotational energy. Astronomers believe that gravity waves are what is carrying away this energy.
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- Another application for the precision of Pulsars depends on Pulsars being scattered throughout the Galaxy. When gravity waves pass by a mass they compress it sideways and then elongate it lengthwise as the wave passes through. Physicists are using kilometer long laser beams perpendicular to each other in order to detect these gravity wave distortions on Earth. Astronomers are trying to do the same experiment with Pulsars in the Galaxy.
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- If gravity waves are traveling past these Pulsars they will move the Pulsars with the passing wave, not unlike a buoy on a water wave. This movement can be detected as a change in frequency of the Pulsar’s radio wave . This is the Doppler Effect and a very slight variation in the timing of the pulse. If this can be detected it can by measured for a line of Pulsars that are each effected by the gravity wave in sequence. The gravity wave would be traveling across the Galaxy at the speed of light.
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- The wavelength of gravity waves is very long, and therefore the frequency is very low.
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- The first pulsar was discovered in 1967 and astronomers have been studying them ever since. They come up with theories that with precise measurement rule out some proposals and pursue new ones. The process in science is never ending. The more we learn the more we need to know.
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- Newton said the discover was like finding shells on the beach with a whole ocean of new knowledge out in front of you.
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707-536-3272, Thursday, March 15, 2012
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