10
1 Introduction to the Pulsars
(1) The typical pulse periods of pulsars are from 1.6 ms to 8.5 s.
(2) The pulse periods are always increased slowly, and the contrary cases have not
been observed. Of course, it is an exception which pulsars happen accidentally
the glitches of periods.
(3) The pulsars are the astronomical clocks with extremely stable periodicity, and
for the decimal fraction of second of their pulsating periods, the 13th–21st
significant digits have been observed.
During a pulse period of 1.6 ms, transmission distance of light is 480 km. The
value is the upper limit of size of the source emitting the pulsating signals. Moreover,
the pulsars are the astronomical clocks with extremely stable periodicity, and hence
the relation between the emitting source and its whole body source must have been
inter-coupling. So, the candidates of the pulsars are only possible the compact stars,
including white dwarf, neutron star and black hole.
If a compact star in the universe behaves as an astronomical clock with extremely
stable periodicity, there are only three possible mechanisms: pulsation, rotation and
binary system. According to Eddington’s stellar pulsation equation, the relation
between the pulsating period and the celestial average density can be expressed
as
P =
C
√ ρ
,
(1.1)
where P is the stellar pulsation period, ρ is the stellar average density, and C is the
constant.
According to expression (1.1), if the density of the white dwarf is used to calculate
the stellar pulsation period, the period is the order of 10 s and it is impossible for
the period to be less than 1 s. If the density of the neutron star is used, the periodic
range is 1−10 ms. Comparing to the pulse periods for most of the discovered pulsars,
the calculating periods of the white dwarfs are not accordant with the observational
facts, while those of the neutron stars are too short indeed. Therefore, the pulsation
is firstly eliminated in three mechanisms.
Generally, the rotational angular velocities of stars will not be greater than a certain
critical value, which is decided by the balance conditions between the gravitational
and centrifugal forces on the equatorial matters. For a rotating star with dynamics
stability, the lower limit of its rotating period is
P
3π
Gρ
,
(1.2)
where P is the stellar rotational period, ρ is the stellar average density and G is the
gravitational constant.
According to inequality (1.2), the lower limit of the rotational period is calculated
as 1 s for the white dwarfs, but the pulse periods of many pulsars are less than 1 s; for
1 Introduction to the Pulsars
(1) The typical pulse periods of pulsars are from 1.6 ms to 8.5 s.
(2) The pulse periods are always increased slowly, and the contrary cases have not
been observed. Of course, it is an exception which pulsars happen accidentally
the glitches of periods.
(3) The pulsars are the astronomical clocks with extremely stable periodicity, and
for the decimal fraction of second of their pulsating periods, the 13th–21st
significant digits have been observed.
During a pulse period of 1.6 ms, transmission distance of light is 480 km. The
value is the upper limit of size of the source emitting the pulsating signals. Moreover,
the pulsars are the astronomical clocks with extremely stable periodicity, and hence
the relation between the emitting source and its whole body source must have been
inter-coupling. So, the candidates of the pulsars are only possible the compact stars,
including white dwarf, neutron star and black hole.
If a compact star in the universe behaves as an astronomical clock with extremely
stable periodicity, there are only three possible mechanisms: pulsation, rotation and
binary system. According to Eddington’s stellar pulsation equation, the relation
between the pulsating period and the celestial average density can be expressed
as
P =
C
√ ρ
,
(1.1)
where P is the stellar pulsation period, ρ is the stellar average density, and C is the
constant.
According to expression (1.1), if the density of the white dwarf is used to calculate
the stellar pulsation period, the period is the order of 10 s and it is impossible for
the period to be less than 1 s. If the density of the neutron star is used, the periodic
range is 1−10 ms. Comparing to the pulse periods for most of the discovered pulsars,
the calculating periods of the white dwarfs are not accordant with the observational
facts, while those of the neutron stars are too short indeed. Therefore, the pulsation
is firstly eliminated in three mechanisms.
Generally, the rotational angular velocities of stars will not be greater than a certain
critical value, which is decided by the balance conditions between the gravitational
and centrifugal forces on the equatorial matters. For a rotating star with dynamics
stability, the lower limit of its rotating period is
P
3π
Gρ
,
(1.2)
where P is the stellar rotational period, ρ is the stellar average density and G is the
gravitational constant.
According to inequality (1.2), the lower limit of the rotational period is calculated
as 1 s for the white dwarfs, but the pulse periods of many pulsars are less than 1 s; for