Stages of thermonuclear energy generation in stars

The different burning stages depend on the mass of the stars. In Table 8.2 some examples are given. It is seen that oxygen burning lasts only several months. 

The final evolution of massive stars (see e.g. the review given by Woosley, Heger, and Weaver, 2002 [366]) becomes more violent than that for low massive stars. A cosmic catastrophe occurs. The gas of the Fe core becomes electron degenerate. As soon as it exceeds about the mass of 1.4 solar masses (this is called Chandrasekhar mass), i.e. the core exceeds the size of the Earth, gravity is too strong to 

For our investigations about the chemical elements in the universe, especially hydrogen and oxygen, supernovae are extremely interesting since they eject newly 

As long as the core left behind the supernova explosion is less than about three solar masses, the collapse will be stopped by the pressure of degenerate neutrons. Thus a neutron star is formed which is a very compact object with a radius of only 10 km. Pulsars are rapidly rotating neutron stars. A famous example of a supernova remnant is the Crab nebula. The shell of this nebula expands at velocities of up to 1500 km/s. The filaments contain anomalously high abundances of helium and other more massive chemical elements. The Crab Pulsar rotates 30 times a second (see Fig. 8.9). The Crab Pulsar (PSR B0531-I-21) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054 and it was observed e.g. by ancient Chinese astronomers. 

Supernova remnants sometimes show water emission (shock excited, e.g. in the supernova remnant 3 C 391, Reach and Rho, 1998 [277]). Woodall and Gray, 2007 [364] investigated 18 known supernova remnants for evidence of the 22.235-GHz water maser spectral line, using the 20-m telescope at the Onsala observatory in Sweden. Their results were negative, which was consistent with their theoretical models. Only in unusual environments can 22-GHz water masers be detected around supernova remnants. The Very Large Array was also used to search for water masers in the three supernova remnants W28, W44, and IC 443. Only one candidate maser was detected, in W44. Follow-up observations using the VLA at 1612 MHz demonstrate that the water maser in W44 is likely associated with a late-type star and not a shock in the supernova remnant (Claussen et al., 1999 [70]). 

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Table Stages of thermonuclear energy generation in stars...

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