1.2 The Discovery and Identification
9
and radio astronomers immediately turned their attentions to confirming the remarkable results. At that time, the world’s large radio telescopes almost pointed together
to the pulsar located in the constellation of Vulpecula, now known as PSR B1919+21,
where PSR stands for Pulsating Source of Radio, the letter “B” stands for the 1950
system of coordinates, and the numbers “1919+21” stands for its position, right
ascension and declination. The tide of pulsar observation was set off widely in a
short time, and many papers on the observation report and theoretical analysis of the
pulsars were published in various kinds of astronomical journals. Only a fortnight
separated from the first paper, and another paper from the Jodrell Bank Observatory
gave some remarkable extra details of the radio pulses from the first pulsar in the
Nature. By the end of 1968, total papers related to the pulsars were published more
than 100, and the number of pulsars discovered got to 23 [8].
Particularly, two significant pulsars, Vela Pulsar and Crab Pulsar, were found at the
time. The Vela Pulsar is associated with the Vela supernova remnant in the constellation of Vela, which the supernova explosion is estimated about 11,000−12,300 years
ago. The association of the Vela pulsar with the Vela supernova remnant, which was
made by astronomers at the University of Sydney in 1968, was the first direct observational proof that the neutron stars came from the supernova explosions [9]. The
Vela Pulsar has the emitting signals in the radio, visible light, X-ray and gamma-ray
energy -bands, in which the gamma ray is the brightest in the high-energy gamma-ray
sky and the visible light is the third brightness of all known pulsars. Its pulse period
and distance are respectively about 89.33 ms and 959 light-years. The Crab Pulsar
is the central star in the Crab Nebula , and a remnant of the supernova explosion
which was observed by astronomers of the Song Dynasty in China in 1054 [10]. The
Crab Pulsar is a relatively young neutron star, and its pulse period and distance are
respectively about 33.7 ms and 7100 light-years. The Crab Nebula is often used as
a calibration source in X-ray astronomy, which is very bright in X-rays, and its flux
density and spectrum are known to be constant, of course, with the exception of the
pulsar itself. The pulsar provides a strong periodic signal that is used to check the
timing of the X-ray detectors.
After the pulsar was discovered in the Crab Nebula, could Pacini’s prediction
in 1967 be verified? It was a fundamental issue on the pulsars identified as the
neutron stars, and also a problem which most astronomers and astrophysicists would
endeavor to solve at that time. In 1968, an Australian-born astrophysicist Thomas
Gold (1920−2004) independently presented that the pulsars are the rapidly rotating
neutron stars and the magnetic flux density on their surface about 10
8 T [11]. Gold’s
neutron star model, similar to Pacini’s model published in 1967 [4], explicitly argued
that this model could explain the pulsating radiation observed by Jocelyn Bell and
Hewish. Many observation features, especially the stability of pulse period, can be
explained using the models of rotating neutron stars. The pulse period will increase a
few as the pulsar loses gradually its spinning energy. In 1969, Gold also pointed out
that the energy loss of the Crab Pulsar was roughly equal to the energy consumption
of the Crab Nebula. And thus, it is basically accepted that the pulsars are the rapidly
rotating neutron stars. In fact, the observational evidence that the pulsars are identified
as neutron stars mainly come from the following three points:
9
and radio astronomers immediately turned their attentions to confirming the remarkable results. At that time, the world’s large radio telescopes almost pointed together
to the pulsar located in the constellation of Vulpecula, now known as PSR B1919+21,
where PSR stands for Pulsating Source of Radio, the letter “B” stands for the 1950
system of coordinates, and the numbers “1919+21” stands for its position, right
ascension and declination. The tide of pulsar observation was set off widely in a
short time, and many papers on the observation report and theoretical analysis of the
pulsars were published in various kinds of astronomical journals. Only a fortnight
separated from the first paper, and another paper from the Jodrell Bank Observatory
gave some remarkable extra details of the radio pulses from the first pulsar in the
Nature. By the end of 1968, total papers related to the pulsars were published more
than 100, and the number of pulsars discovered got to 23 [8].
Particularly, two significant pulsars, Vela Pulsar and Crab Pulsar, were found at the
time. The Vela Pulsar is associated with the Vela supernova remnant in the constellation of Vela, which the supernova explosion is estimated about 11,000−12,300 years
ago. The association of the Vela pulsar with the Vela supernova remnant, which was
made by astronomers at the University of Sydney in 1968, was the first direct observational proof that the neutron stars came from the supernova explosions [9]. The
Vela Pulsar has the emitting signals in the radio, visible light, X-ray and gamma-ray
energy -bands, in which the gamma ray is the brightest in the high-energy gamma-ray
sky and the visible light is the third brightness of all known pulsars. Its pulse period
and distance are respectively about 89.33 ms and 959 light-years. The Crab Pulsar
is the central star in the Crab Nebula , and a remnant of the supernova explosion
which was observed by astronomers of the Song Dynasty in China in 1054 [10]. The
Crab Pulsar is a relatively young neutron star, and its pulse period and distance are
respectively about 33.7 ms and 7100 light-years. The Crab Nebula is often used as
a calibration source in X-ray astronomy, which is very bright in X-rays, and its flux
density and spectrum are known to be constant, of course, with the exception of the
pulsar itself. The pulsar provides a strong periodic signal that is used to check the
timing of the X-ray detectors.
After the pulsar was discovered in the Crab Nebula, could Pacini’s prediction
in 1967 be verified? It was a fundamental issue on the pulsars identified as the
neutron stars, and also a problem which most astronomers and astrophysicists would
endeavor to solve at that time. In 1968, an Australian-born astrophysicist Thomas
Gold (1920−2004) independently presented that the pulsars are the rapidly rotating
neutron stars and the magnetic flux density on their surface about 10
8 T [11]. Gold’s
neutron star model, similar to Pacini’s model published in 1967 [4], explicitly argued
that this model could explain the pulsating radiation observed by Jocelyn Bell and
Hewish. Many observation features, especially the stability of pulse period, can be
explained using the models of rotating neutron stars. The pulse period will increase a
few as the pulsar loses gradually its spinning energy. In 1969, Gold also pointed out
that the energy loss of the Crab Pulsar was roughly equal to the energy consumption
of the Crab Nebula. And thus, it is basically accepted that the pulsars are the rapidly
rotating neutron stars. In fact, the observational evidence that the pulsars are identified
as neutron stars mainly come from the following three points: