What happens when a pulsar dies

The dying of the stars

What happens when a star dies?

After a while, the energy of the gas atoms in the center is so high that they can overcome the electrostatic repulsion that exists between their nuclei due to the charge of the same name. The atomic nuclei come so close that they can fuse to form a new, heavier atomic nucleus. This is called merging. This process happens at temperatures of several million degrees. The hydrogen fuses to form helium, the next heavier element. The radiation released in the process stabilizes the star against gravity, so there is an equilibrium between the contracting gravity and the radiation pressure that is driving apart. For the fusion of hydrogen to helium, the so-called hydrogen burning, to start, a mass of at least 0.08 solar masses is necessary. The zone inside the star where fusion takes place is surrounded by a layer of non-fusing hydrogen. Here the temperature is not high enough to ignite fusions. In our sun, the fusion zone extends over about a quarter of the visible diameter. Depending on the mass, some become red giants and some become white dwarfs.

Red giant: When a star's nuclear fuel (hydrogen) is depleted at the end of its life, it slowly expands its outer layers, cooling them down and decreasing their density. The star swells into a red giant. Our sun will do the same in a few billion years. It will then probably extend to the earth's orbit. The surface temperatures of red giants are between 2,000 and 3,500 Kelvin. Due to the low temperature, red giants have less radiation in visible light. But since they have an extremely large surface, they emit a lot of light and are therefore very bright.
Examples of red giants are the star Aldebaran in the constellation Taurus, Arcturus in the constellation Bootes or Mira in the constellation Whale.



White dwarf: A white dwarf is a small star that, despite its high surface temperature, which can be between 8,000 and 50,000 Kelvin, only has a low luminosity. It represents the last station in the evolution of low-mass stars. A white dwarf evolves from a red giant that sheds its outer shell, leaving the core behind. It has a mass of less than 1.44 solar masses. They appear in white bluish color. Since they no longer have an additional source of energy, they cool down within billions of years and end up cold as black dwarfs. This is how our sun will end too.


Neutron stars
A neutron star has a very high density and is between 1.2 and 2 solar masses and only 10 to 20 kilometers in diameter. The mean density of a neutron star is around 3.7 to 5.9 * 1017 kg / m3 and thus has the highest possible density for an object without an event horizon. However, they rotate very quickly and also have a very strong magnetic field. For example, a neutron star discovered in 2004 has a rotation speed of 716 revolutions per second. Since the gravitational field on the surface of a neutron star is about 20 * 1011 is stronger than that of our earth, an object would have to have an escape speed of about 100,000 km / s to be able to leave the neutron star (about 1/3 the speed of light).
There are also other types of neutron stars:
The pulsar that arises when the axis of symmetry of its magnetic field deviates from the axis of rotation, which is why it emits synchrotron radiation along the dipole axis.
The magnetars that arise with an initial rotation period of less than 10 ms. In this case, a special dynamo effect also converts the energy of convection currents inside the star into magnetic energy.
The quark stars, if in addition to the neutron matter there is also a core of quark-gluon plasma in the center. However, this star has not yet been proven and is just one possible theory.
The X-ray Dim Isolated Neutron Stars (XDINS, German X-ray weak isolated neutron stars) which only have a purely thermal X-ray radiation and a luminosity between 1030 and 1032 erg-1


Black hole
A black hole is a massive star at the end of its life, it explodes in a supernova and sheds its outer layers. If that happened to our sun, it would only have a diameter of 3 km, but as already mentioned it would succumb to a less dramatic fate. Black holes can also arise when two stars collide and their masses unite. If this mass then exceeds a certain value, this new star collapses into a black hole. Black holes consist of a lot of mass that is strongly compressed by gravity. Since the gravity is too strong for light reflections, you cannot see the black hole and everything that is in it. The main reason is the Schwarzschild radius of static black holes. In addition, the mass attracts more and more mass, which makes it bigger and bigger.