High_Mass_Stars - The Death of High Mass Stars Chapter 11...

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The Death of High Mass Stars Chapter 11
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Recall that a solar mass star ends with a Carbon core, the final element to be produced via nuclear reactions. This carbon core remains after the planetary nebula phase as a white dwarf supported by electron degeneracy pressure. In higher mass stars (8 to 30 M ), outer layers of star squeeze and heat the core to ignite Carbon…then Oxygen, Neon, etc. As each fuel gets exhausted in the core, its burning moves to a shell -Onion skin structure Formation of Iron is the final stage
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Why is Iron formation the end of the line? 56 Fe has the highest binding energy per nucleon - very stable. Any reaction involving iron (fission or fusion) requires energy. With no more sources of energy, and Fe fusion taking energy from the gas, pressure support in the star’s core is lost. The core quickly collapses under its own weight….
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If the core mass is greater than the Chandrasekhar limit (1.44M ) the core cannot be supported by electron degeneracy pressure - core continues to collapse. The 56 Fe atoms use any energy produced in the collapse, so the core does not heat up. Iron atoms get destroyed in the ever collapsing core and the protons then combine with electrons in the star to produce neutrons and neutrinos e- + p = n + ν Eventually, the neutrons are so close together they “touch”: neutron degeneracy pressure. The neutron core then halts the collapse causing outer material to bounce outward.
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Supernova! - Type II During the explosion, nuclear reactions take place rapidly and can produce elements heavier than iron. Material is dispelled into ISM to be incorporated into later generations of stars. Crab Nebula - result of a supernova recorded by Chinese astronomers in 1054 AD
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A supernovae explosion can exceed the luminosity of an entire galaxy - 10 53 ergs Lightcurves show a rapid increase in brightness followed by fading over several months. 1% is in kinetic energy within the remnant and just 0.1% is released in light. Much energy is transported via escaping neutrinos.
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Supernova Remnants Generally have strong magnetic fields and contain many charged particles Electrons spiral around the field lines - spiraling motion of charged particles produces synchrotron radiation - polarized light Optical - IR - CasA Veil Nebula X-ray - CasA Radio - CasA Optical - SN1987A
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Synchrotron Radiation Power-law with most radiation given off at long wavelengths While most light is in the radio, the Crab Nebula is bright enough to detect synchrotron radiation into gamma-rays
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High_Mass_Stars - The Death of High Mass Stars Chapter 11...

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