4
1 Introduction to the Pulsars
with the protons. Of course, the high pressure could not be obtained on the ground,
but there are possibly the celestial bodies with the extreme physical conditions in
the universe. Therefore, it would certainly be imagined from the neutrons inside the
atomic nuclei that there are possibly the neutron stars in the universe.
After Chadwick just declared his discovery, the Soviet physicist Lev Davidovich
Landau (1908−1968) theoretically proposed the predictions: there is possibly a
stable celestial body consisted of the neutrons in the universe, neutron star; it has
a very small size, high density and faint radiation. In 1934, the German astronomer
Walter Baade (1893−1960) and the Swiss astronomer Fritz Zwicky (1898−1974)
proposed the existence of a new form of the neutron star, which would be the endpoint
of stellar evolution. They wrote in the papers [2, 3]:
…with all reserve we advance the view that a supernova represents the transition of an
ordinary star into a neutron star, consisting mainly of neutrons. Such a star may possess a
very small radius and an extremely high density.
In 1939, the American theoretical physicist Julius Robert Oppenheimer
(1904−1967) and his student George Volkoff (1914−2000) assumed that the
neutrons in a neutron star formed a degenerate cold Fermi gas, and first worked
out the mass, density and diameter of the neutron star using a simple equation of
state. Thereby, the model of the neutron star was created theoretically. The model
needed to be verified by actual observations. And thus, this made astronomers so
warm and high that they searched prospectively the neutron stars using optical telescopes. Unfortunately, the candidate objects like white dwarfs were only observed.
It was shown from analyzing the observation data that the pressure inside the white
dwarfs could not furthest reach the required order of neutron stars. Except for the
white dwarfs, other candidate objects were also found no longer. It is well known
that the luminosity of a star is proportional to its surface area. Typically, the radius
of a neutron star is only 10 km. And thereby, its surface area is so small that its luminosity is only a part of billions compared to an ordinary star. At that time, optical
telescopes were the main equipment for astronomical observations, and hence the
neutron stars predicted in the universe could not be discovered naturally. Neutron
stars were thought to be too faint to be detectable and then little work was done on
them.
Until 1967, just before the pulsar discovery, the Italian astrophysicist Franco
Pacini (1939−2012) published a paper titled “Energy Emission of a Neutron Star”
in Nature [4]. He pointed out in this paper: if neutron stars were spinning and had large
magnetic fields, then electromagnetic waves would be emitted; the rapid rotation of
highly magnetic neutron stars might be the source of energy in the Crab Nebula.
Unbeknown to him, the radio astronomer Antony Hewish and his research assistant
Jocelyn Bell at the University of Cambridge were shortly to detect radio pulses from
the stars that are now believed to be highly magnetized, rapidly spinning neutron
stars, known as pulsars.
In the past 35 years since the neutrons were discovered, the neutron stars had not
been found. Meanwhile, the density of the neutron stars was so extremely high from
the theoretical model that it was surprising. Therefore, the hypothesis that there were
1 Introduction to the Pulsars
with the protons. Of course, the high pressure could not be obtained on the ground,
but there are possibly the celestial bodies with the extreme physical conditions in
the universe. Therefore, it would certainly be imagined from the neutrons inside the
atomic nuclei that there are possibly the neutron stars in the universe.
After Chadwick just declared his discovery, the Soviet physicist Lev Davidovich
Landau (1908−1968) theoretically proposed the predictions: there is possibly a
stable celestial body consisted of the neutrons in the universe, neutron star; it has
a very small size, high density and faint radiation. In 1934, the German astronomer
Walter Baade (1893−1960) and the Swiss astronomer Fritz Zwicky (1898−1974)
proposed the existence of a new form of the neutron star, which would be the endpoint
of stellar evolution. They wrote in the papers [2, 3]:
…with all reserve we advance the view that a supernova represents the transition of an
ordinary star into a neutron star, consisting mainly of neutrons. Such a star may possess a
very small radius and an extremely high density.
In 1939, the American theoretical physicist Julius Robert Oppenheimer
(1904−1967) and his student George Volkoff (1914−2000) assumed that the
neutrons in a neutron star formed a degenerate cold Fermi gas, and first worked
out the mass, density and diameter of the neutron star using a simple equation of
state. Thereby, the model of the neutron star was created theoretically. The model
needed to be verified by actual observations. And thus, this made astronomers so
warm and high that they searched prospectively the neutron stars using optical telescopes. Unfortunately, the candidate objects like white dwarfs were only observed.
It was shown from analyzing the observation data that the pressure inside the white
dwarfs could not furthest reach the required order of neutron stars. Except for the
white dwarfs, other candidate objects were also found no longer. It is well known
that the luminosity of a star is proportional to its surface area. Typically, the radius
of a neutron star is only 10 km. And thereby, its surface area is so small that its luminosity is only a part of billions compared to an ordinary star. At that time, optical
telescopes were the main equipment for astronomical observations, and hence the
neutron stars predicted in the universe could not be discovered naturally. Neutron
stars were thought to be too faint to be detectable and then little work was done on
them.
Until 1967, just before the pulsar discovery, the Italian astrophysicist Franco
Pacini (1939−2012) published a paper titled “Energy Emission of a Neutron Star”
in Nature [4]. He pointed out in this paper: if neutron stars were spinning and had large
magnetic fields, then electromagnetic waves would be emitted; the rapid rotation of
highly magnetic neutron stars might be the source of energy in the Crab Nebula.
Unbeknown to him, the radio astronomer Antony Hewish and his research assistant
Jocelyn Bell at the University of Cambridge were shortly to detect radio pulses from
the stars that are now believed to be highly magnetized, rapidly spinning neutron
stars, known as pulsars.
In the past 35 years since the neutrons were discovered, the neutron stars had not
been found. Meanwhile, the density of the neutron stars was so extremely high from
the theoretical model that it was surprising. Therefore, the hypothesis that there were