1.4 The Physical Mechanisms and Characteristics
27
of 15 km, it is computed easily that its density is 2 × 10
11 kg/cm
3 and its surface
acceleration 8.3 × 10
8 km/s
2 . Apparently, the atmospheric pressure of neutron star
is decreased so rapidly that its atmospheric thickness is only 0.1−10 cm and average
density 0.01−100 g/cm
3 . As same as an ordinary star, the thermal radiation of neutron
star comes from its atmosphere, and thus the characteristics of X-ray radiation will
be decided by the atmosphere. So, the basic components and characteristics of the
neutron star’s atmosphere can be detected by observing its thermal radiation.
Below the atmosphere of neutron star, the matter in the zone with a density of
less than 4.3 × 10
8 kg/cm
3 consists of nuclei and electrons, and thereby the zone is
called outer crust layer, with a thickness of about 0.3 km. If the temperature of the
outer crust layer is lower than the dissolution temperature, a solid state will occur. In
the outer crust layer, the Coulomb lattice of heavy atomic nucleus is always balanced
with relativistic-degenerate electron gas each other.
With the density increasing, the Fermi energy of electrons will rise, and the number
of protons inside atomic nucleus also increases. When the density of matter is higher
than 4.0 × 10
8 kg/cm
3 , with the neutron number increasing, a part of neutrons will
almost drip out from the atomic nuclei. This density is usually referred to as the
neutron drip density. When the density further increases and approaches to the
density of atomic nuclei, all protons inside the atomic nuclei are almost neutronized
and neutrons free out of the nuclei. Finally, the atomic nuclei themselves will disappear. The inner crust layer is a zone composed of the nuclear lattice with neutron
rich, super-fluid neutron gas and electron gas. The thickness of the zone is about
1 km, and its density is between the neutron drip density and the atomic nucleus one.
The density of the inner crust layer has continuously gone up to that of the atomic
nuclei. In the zone where the density has been higher than the density of the atomic
nuclei, there are not any atomic nuclei; most parts of the zone are composed of
anisotropic super-fluid neutrons, and there are a small amount of super-fluid protons
and positrons. The zone is usually called neutron matter region, with a thickness of
about thousands of meters. Neutrons are main matter in the region, and the population
of neutrons is 8 times that of protons in an extreme case.
With the depth increasing, the density inside neutron stars also continuously rises.
When the density is more than 2−3 times the density of atomic nuclei, energy per
unit baryon will be very low, and thus bring up various subatomic particles, such
as quark matter, pi meson or kappa meson condensation, hyperon matter, and so
on. Under so high density, neutrons may be squeezed to form mesons or kaons and
further a solid core. This zone is usually referred to as core region, with a thickness
of about 1 km.
The quarks would naturally be “up” and “down”, but they might change into
the “strange” variety. Currently, there are two main views on the quark matter of
possibly occurring inside neutron stars. For one view, there are the first-order phase
transitions in the core regions of neutron stars and the phase transitions between
nucleon matter and quark matter are separated by a cross-section of discontinuous
density. The types of these neutron stars are usually called mixed stars. For another
view, it is possible from macro-scale that both the nucleon matter and the quark
matter inside neutron stars can exist together, and thus the density from the nucleon
27
of 15 km, it is computed easily that its density is 2 × 10
11 kg/cm
3 and its surface
acceleration 8.3 × 10
8 km/s
2 . Apparently, the atmospheric pressure of neutron star
is decreased so rapidly that its atmospheric thickness is only 0.1−10 cm and average
density 0.01−100 g/cm
3 . As same as an ordinary star, the thermal radiation of neutron
star comes from its atmosphere, and thus the characteristics of X-ray radiation will
be decided by the atmosphere. So, the basic components and characteristics of the
neutron star’s atmosphere can be detected by observing its thermal radiation.
Below the atmosphere of neutron star, the matter in the zone with a density of
less than 4.3 × 10
8 kg/cm
3 consists of nuclei and electrons, and thereby the zone is
called outer crust layer, with a thickness of about 0.3 km. If the temperature of the
outer crust layer is lower than the dissolution temperature, a solid state will occur. In
the outer crust layer, the Coulomb lattice of heavy atomic nucleus is always balanced
with relativistic-degenerate electron gas each other.
With the density increasing, the Fermi energy of electrons will rise, and the number
of protons inside atomic nucleus also increases. When the density of matter is higher
than 4.0 × 10
8 kg/cm
3 , with the neutron number increasing, a part of neutrons will
almost drip out from the atomic nuclei. This density is usually referred to as the
neutron drip density. When the density further increases and approaches to the
density of atomic nuclei, all protons inside the atomic nuclei are almost neutronized
and neutrons free out of the nuclei. Finally, the atomic nuclei themselves will disappear. The inner crust layer is a zone composed of the nuclear lattice with neutron
rich, super-fluid neutron gas and electron gas. The thickness of the zone is about
1 km, and its density is between the neutron drip density and the atomic nucleus one.
The density of the inner crust layer has continuously gone up to that of the atomic
nuclei. In the zone where the density has been higher than the density of the atomic
nuclei, there are not any atomic nuclei; most parts of the zone are composed of
anisotropic super-fluid neutrons, and there are a small amount of super-fluid protons
and positrons. The zone is usually called neutron matter region, with a thickness of
about thousands of meters. Neutrons are main matter in the region, and the population
of neutrons is 8 times that of protons in an extreme case.
With the depth increasing, the density inside neutron stars also continuously rises.
When the density is more than 2−3 times the density of atomic nuclei, energy per
unit baryon will be very low, and thus bring up various subatomic particles, such
as quark matter, pi meson or kappa meson condensation, hyperon matter, and so
on. Under so high density, neutrons may be squeezed to form mesons or kaons and
further a solid core. This zone is usually referred to as core region, with a thickness
of about 1 km.
The quarks would naturally be “up” and “down”, but they might change into
the “strange” variety. Currently, there are two main views on the quark matter of
possibly occurring inside neutron stars. For one view, there are the first-order phase
transitions in the core regions of neutron stars and the phase transitions between
nucleon matter and quark matter are separated by a cross-section of discontinuous
density. The types of these neutron stars are usually called mixed stars. For another
view, it is possible from macro-scale that both the nucleon matter and the quark
matter inside neutron stars can exist together, and thus the density from the nucleon