Astroparticle Physics

66 5 Acceleration Mechanismsprovided by the cyclotron mechanism. The mechanism ofapproaching sunspots, however, sounds more plausible becausein this case no guiding forces (like in the cyclotronmodel) are required.5.3 Shock Acceleration“Basic research is what I am doingwhen I don’t know what I am doing.”Wernher von Braungravitational collapsesuccessive fusion processesbirth of neutron starsformation of heavy elementsneutron attachmentIf a massive star has exhausted its hydrogen, the radiationpressure can no longer withstand the gravitational pressureand the star will collapse under its own gravity. The liber-ated gravitational energy increases the central temperatureof a massive star to such an extent that helium burning canstart. If the helium reservoir is used up, the process of gravi-tational infall of matter repeats itself until the temperature isfurther increased so that the products of helium themselvescan initiate fusion processes. These successive fusion processescan lead at most to elements of the iron group (Fe,Co, Ni). For higher nuclear charges the fusion reaction isendotherm, which means that without providing additionalenergy heavier elements cannot be synthesized. When thefusion process stops at iron, the massive star will implode.In this process part of its mass will be ejected into interstellarspace. This material can be recycled for the productionof a new star generation which will contain – like the Sun –some heavy elements. As a result of the implosion a com-pact neutron star will be formed that has a density which iscomparable to the density of atomic nuclei. In the course ofa supernova explosion some elements heavier than iron areproduced if the copiously available neutrons are attached tothe elements of the iron group, which – with successive β −decays – allows elements with higher nuclear charge to beformed:56265726582657Fe + n → 26 Fe ,58Fe + n → 26 Fe ,59Fe + n →26 Fe∗ (5.5)✲ 5927 Co + e− +¯ν e ,5927 Co + n →6027 Co∗✲ 6028 Ni + e− +¯ν e .