The Physics Factbook
Edited by Glenn Elert -- Written by his students
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|Wielebinski, Richard. The Characteristics of (Normal) Pulsars. arXiv:astro-ph/0208557 v1 30, (August 2002): 25, 2.||"The periods of pulsars are remarkably stable, in the range 0.0015 sec to 8.51 sec. The pulsar period has been found to change (increase) as a result of loss of rotational energy. This period derivative P(dot) is a very important parameter for the determination of the pulsar age."||0.0015–8.51 s|
|The ATNF Pulsar Database. The Australia Telescope National Facility (ATNF), 28 May 2007.||[see graph below]||0.8097 ± 1.0396 s
|The Sounds of Pulsars. The University of Manchester - Jodrell Bank Observatory, 28 May 2007.||"PSR B0329+54
This pulsar is a typical, normal pulsar, rotating with a period of 0.714519 seconds, i.e. close to 1.40 rotations/sec."
|"PSR B0833-45, The Vela Pulsar
This pulsar lies near the centre of the Vela supernova remnant, which is the debris of the explosion of a massive star about 10,000 years ago. The pulsar is the collapsed core of this star, rotating with a period of 89 milliseconds or about 11 times a second."
|"PSR B0531+21, The Crab Pulsar
This is the youngest known pulsar and lies at the centre of the Crab Nebula, the supernova remnant of its birth explosion, which was witnessed by Europeans and Chinese in the year 1054 A.D. as a day-time light in the sky. The pulsar rotates about 30 times a second."
This is a recently discovered millisecond pulsar, an old pulsar which has been spun up by the accretion of material from a binary companion star as it expands in its red giant phase. The accretion process results in orbital angular momentum of the companion star being converted to rotational angular momentum of the neutron star, which is now rotating about 174 times a second."
This is the second fastest known pulsar, rotating with a period of 0.00155780644887275 seconds, or about 642 times a second. The surface of this star is moving at about 1/7 of the velocity of light and illustrates the enormous gravitational forces which prevent it flying apart due to the immense centrifugal forces. The fastest-rotating pulsar is PSR J1748-2446ad, which rotates about 10% faster at 716 times a second."
|Gutsch, William A. 1001 Things Everyone Should Know About the Universe. New York: Doubleday, 1998.||"A pulsar was soon found inside the Crab Nebula and it held a surprise of its own. In 1968, inspired by Joycelyn Bell's discovery and the models of pulsars (a.k.a. neutron stars) conjured up by the theoreticians, observational astronomers had a closer look at that little star Walter Baade had pointed out back in 1942. Baade's star was indeed pulsing away at the remarkable rate of thirty times a second. And surprisingly, the star not only appeared to be flashing on and off in radio waves but was doing so in visible light as well like some kind of hyperactive disco strobe light. The reason that no one had noticed the flashing before was that its rate of blinking was simply too fast for the human eye to catch, so to the eye, as well as in pictures taken with time exposures, the star appeared to be 'always on.'"||0.333 s|
|The Discovery of Pulsars. British Broadcasting Corporation (BBC), 28 May 2007||"Bell later mentioned her findings to Hewish, and they decided to set up a high-speed recorder. However, they failed to pick up the signal again for several months. When Bell returned from a Christmas holiday - during which time Hewish had decided to keep the recorders running - she finally found what she had been looking for. A clear series of rapid pulses, each about 1/3 of a second long, all equal in strength, and with equal spacing of around a second. This behaviour had never been seen in nature before."||0.333 s|
A pulsar is a neutron star that rotates and emits radiation. Pulsars were discovered in 1967 by Jocelyn Bell Burnell and Antony Hewish. They received periodic signals coming from outer space while using a radio telescope to learn about quasars.
As a massive star loses it's ability to undergo fusion, it collapses in a supernovae explosion due to its own gravitational force. In some cases, the core of the star remains and as it cools, it shrinks in size while retaining its mass. Since a large amount of mass is concentration in a small space, the force of gravity on it increases (g = Gm/r2). When the force of gravity becomes so great that the protons and the electrons of the star's atoms merge to form neutrons, the result is a "neutron" star.
Since the neutron star has less mass, but the same angular momentum as the star from which it originated, the neutron star must have a greater angular velocity
L1 = r1m1v1 = L2 = r2m2v2
Being so dense, a neutron star can have a large angular velocity without being broken apart by its centrifugal force.
The neutron star has a powerful magnetic field and as the star spins rapidly, the magnetic field generates a powerful electric field. Charged particles in the debris left over from the supernovae explosion gets trapped within the electric field and are dragged along as the star rotates. As a charged particle accelerates, it's energy increases and is emitted as electromagnetic radiation. The charged particles are concentrated at the magnetic poles of the neutron star and the energy is emitted as beams of radiation at the poles.
When a beam is detected from the star, it might seem to go on and off, or "pulse," to an observer. This is because the magnetic poles are not aligned with the rotational poles of the star. So as a beam sweeps across space in a circular path, it would only be detected by earth if the beam sweeps across the earth. Once the beam continues on its circular path and moves away from the earth, it would not be detected. Then it would come full circle and be detected again. The periodic motion of the beams is in line with the period of the star's rotation. This results in periodic detections as the beam is directed at and then away from the earth, making the star seem to pulse. Since these stars pulse, they were called "pulsating stars" which led to the name "pulsar." By recording the times a pulsar pulses in a certain time period, the period of the pulsar can be found.
Carol Hsin -- 2007
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