1.2 The Discovery and Identification
11
the neutron stars, their lower limit is 1 ms, despite being close to the critical period,
but up to now, the periods of all discovered pulsars have not been beyond the lower
limit value.
For the binary system of three mechanisms, if the stellar radius is replaced as
the orbital radius of the binary system in estimating the average density, a longer
period can be calculated similarly using inequality (1.2). Since there are no periodic
radiations for the black holes and anything including the electromagnetic waves can
not get away from their event horizons, it is impossible to receive any periodic signals.
In summary, it can be shown from the very regular, stable and short periodicities of
the pulsars that the rapidly rotational neutron stars are uniquely possible candidates.
Certainly, the white dwarfs as the candidates can not be excluded from the pulsars
with the longer rational periods. Currently, it is a well-known conclusion that the
pulsars are the neutron stars.
1.3 The Name, Classification and Distribution
1.3.1 Naming Rules
After the discovery of the pulsar, the naming rule for the pulsars was initially
expressed as “NP rrrr”, where the capital letter “N” will be replaced by initials
of the observatory’s name discovering the pulsar, the capital letter “P” stands for the
word “Pulsar” and “rrrr” is four digits denoting the right ascension of the pulsar in
the 1950.0 coordinate system, in which the first two digits are expressed in hours
and the last two digits in minutes. The names and their capital letters of the observatories early discovering the pulsars are listed in Table 1.1, where “CP 1919” stands
for the first pulsar discovered by Hewish’s research team at Cambridge and its right
ascension is 19h19min, and “NP 0531” stands for the Crab Pulsar discovered by the
National Radio Astronomy Observatory (NRAO) in the United States and its right
ascension is 5h31min. Moreover, it should be noted that the Crab Pulsar was also
often called “NP 0532” in early references as its position was uncertain.
In order to avoid the trouble of using the identifiers with the initial letters of
observatories, “PSR” is directly used to denote the Pulsating Source of Radio (or
Pulsar). And thus, the first discovered pulsar is named “PSR 1919” again. With
discovering more and more population of the pulsars, the four-digit number will
be repeated sometimes if the right ascension is only used to differentiate various
pulsars. And hence, both right ascension and declination are used together in the
naming rules. According to astronomical practice, the positive sign “+” is put on the
front of the northern declination and the negative sign “−” on the front of the southern
declination. Moreover, the significant digits of the declination may be extended
sometimes to 0.1 ° or 0.01 ° to distinguish with adjacent pulsars. As same as marking
the locations of stars, the reference epoch of pulsars’ right ascension and declination
is also considered. In the past, the beginning of the Besselian year with the interval
11
the neutron stars, their lower limit is 1 ms, despite being close to the critical period,
but up to now, the periods of all discovered pulsars have not been beyond the lower
limit value.
For the binary system of three mechanisms, if the stellar radius is replaced as
the orbital radius of the binary system in estimating the average density, a longer
period can be calculated similarly using inequality (1.2). Since there are no periodic
radiations for the black holes and anything including the electromagnetic waves can
not get away from their event horizons, it is impossible to receive any periodic signals.
In summary, it can be shown from the very regular, stable and short periodicities of
the pulsars that the rapidly rotational neutron stars are uniquely possible candidates.
Certainly, the white dwarfs as the candidates can not be excluded from the pulsars
with the longer rational periods. Currently, it is a well-known conclusion that the
pulsars are the neutron stars.
1.3 The Name, Classification and Distribution
1.3.1 Naming Rules
After the discovery of the pulsar, the naming rule for the pulsars was initially
expressed as “NP rrrr”, where the capital letter “N” will be replaced by initials
of the observatory’s name discovering the pulsar, the capital letter “P” stands for the
word “Pulsar” and “rrrr” is four digits denoting the right ascension of the pulsar in
the 1950.0 coordinate system, in which the first two digits are expressed in hours
and the last two digits in minutes. The names and their capital letters of the observatories early discovering the pulsars are listed in Table 1.1, where “CP 1919” stands
for the first pulsar discovered by Hewish’s research team at Cambridge and its right
ascension is 19h19min, and “NP 0531” stands for the Crab Pulsar discovered by the
National Radio Astronomy Observatory (NRAO) in the United States and its right
ascension is 5h31min. Moreover, it should be noted that the Crab Pulsar was also
often called “NP 0532” in early references as its position was uncertain.
In order to avoid the trouble of using the identifiers with the initial letters of
observatories, “PSR” is directly used to denote the Pulsating Source of Radio (or
Pulsar). And thus, the first discovered pulsar is named “PSR 1919” again. With
discovering more and more population of the pulsars, the four-digit number will
be repeated sometimes if the right ascension is only used to differentiate various
pulsars. And hence, both right ascension and declination are used together in the
naming rules. According to astronomical practice, the positive sign “+” is put on the
front of the northern declination and the negative sign “−” on the front of the southern
declination. Moreover, the significant digits of the declination may be extended
sometimes to 0.1 ° or 0.01 ° to distinguish with adjacent pulsars. As same as marking
the locations of stars, the reference epoch of pulsars’ right ascension and declination
is also considered. In the past, the beginning of the Besselian year with the interval