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About Stars: Extreme End-Stages, Supernova

When the iron core of e.g. a red supergiant collapses and has more than 1.44 solar masses (which should be anyway, otherwise it wouldn't have created iron), then something exciting happens. Having not enough heat to resist the pressure, the atoms are cracked. The electrons and the protons are pressed together to form neutrons in a very small space. The hull falls inwards against the shockwave of the collapsing core and therefore fusions immediately - a supernova explosion (of type Ib, Ic or II). A neutron star evolves. This has a very high density and a diameter of only a few kilometers. It is extremely hot and spinning fast, sending hard X-rays out into space. We can see it with the suitable instruments as a regular and fast series of X-ray flashes.
Pulsars are neutron stars which radiate strong radio to x-ray emissions in pulses.

The more massive the neutron star, the smaller it is. This is due to the pressure of its own gravitation. With more than 3.2 solar masses even the neutrons can't stand the pressure and a black hole is generated.

At supernovae of type I, in contrast to type II, no hydrogen can be detected in the remnant. At type Ic helium is missing too. An Ib and Ic supernova is caused by a star with more than maybe 30 solar masses, which before had blown its hull into space (e.g. a Wolf-Rayet star). A type II supernova is caused by a less massive star, a red supergiant.
Supernovae shine for a short time (a few days to weeks) a billion times brighter as the Sun. For a long time after an emission nebula can be viewed. In our galaxy a supernova is expected every 50 years or so.

Examples: Pulsar in the Crab Nebula, Black Hole at Cygnus X-1

Back: About Stars | Continue: Novae
    Ein Neutronenstern
A Neutron Star
Photo: Nasa

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