 Picture made by röntgen telescope of the American satellite Einstein. |
On July 4 of the year 1054, inhabitants in the
far East see a bright shining light in the sky. A star had exploded.
The remainders of that dismanted star or Supernova are today visible as the Crab nebula. The whole Crab nebula, which now has a diameter of fourteen lightyears, still is a röntgen source. This röntgen radiation takes a lot of energy, with the measured radiation level the complete energy of the Crab nebula should be exhausted within a year. However the Crab nebula appears to have at its disposal a sufficient amount of energy to transmit the röntgen radiation for more than ten centuries. This energy is delivered by a tiny röntgen source in the Crab nebula, its the remainder of Supernova: a neutron star. |
Röntgen hot gases.
Neutron stars have more or less the same mass as the Sun (Sun mass), however this mass is packed much more densely, in a sphere of approximately ten kilometers in diameter. In this sphere the atoms have collapsed to neutrons, protons and electrons. At this large density protons react with the electrons so more and more neutrons are formed and finally the neutrons are dominating. Now the core of the neutron star, which is composed of elementary elements, is surrounded by a fluid of primarily neutrons. The fluid itself is encased in a rigid extremely dense crust of a few hundred meters thick.
The gravitational forces at the surface of neutron stars sometimes are billions of times stronger than those of the Sun. Besides neutron stars have very strong magnetic fields. Gas from nearby stars that comes under the influence of these forces is attracted, accelerated in the magnetic atmosphere and then falls freely toward the neutron star. The velocities may rise to one third of the speed of light! Here a lot of energy is generated, the gases are heated up.
The hotter the gas, the shorter the wavelength of the light it transmits. The gas does not get red hot (approx. 1000 kelvin), not even white hot (approx. 10,000 kelvin), and also not 'ultraviolet hot' (approx. 100,000 kelvin). But 'rönt hot' (more than 10,000, 000 kelvin). Thanks to the matter coming from an accompanying star in a binary star system The neutron star functions as a röntgen source.
Pulsars.
The strong magnetic fields of the neutron star run from pole to pole,
same as on Earth (in the picture the green lines). The attracted matter
is forced to fall to the poles (the orange and green surfaces). This causes
small, hot spots on both poles, where röntgen radiation is generated.
The radiation is set free in narrow bundles from the poles of the star
(the blue 'cones').
If the magnetic poles are not lined up with the rotation axis (the
red axis line), the poles rotate sometimes in our line sight and back.
We then see the emitted röntgen radiation as short flashes, varying
with the rotation speed of the neutron star. The pulses reoccur at precise
intervals between 1 millisecond to 4 seconds. Such a source is called
a röntgen pulsar.
Röntgen radiation
from black holes.
With röntgen pulsars the mass of the röntgen source always
appears to be more or less one sun mass and never more than two sun masses.
That is fully in accordance with the theory of neutron stars, because of
the physics of neutrons the stars simply cannot be larger.
Still röntgen sources with much greater masses do exist. These
röntgen sources are black holes.
Also black holes have very strong magnetic and gravitational fields. We
cannot observe the röntgen radiation that is set free near the black
hole. Outside the event horizon however, the radiation is indeed visible.
This radiation is permanently visible, regardless of the rotation speed of
the black hole. That is why black holes cannot be pulsars, nor can pulsars
be black holes.