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Lecture 25

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PHYS 183
Tracy Webb

PHYS 183 – The Milky Way Inside and Out – Tracy Webb Winter 2013 Lecture 25: March 15 , 2013  assignment 3 is up on mycourses  there will only be 2 more assignments  the iron road block o can’t fuse iron o during fusion, mass decreases and energy is released o during fission, mass increases and energy is input o once star builds up iron core there is no way to fuse/fission elements to create energy  no more weapons in gravity-pressure war o in both directions, you liberate energy by changing o once you have the iron core, you are stuck because there are no more fusion reactions that can happen in the core  there is nothing that it can do because it can’t collapse & burn iron o this is when the star essentially dies  death of a high mass star o with pressure support gone, core collapses once again (now ~billion degrees) o core is > 1.4 solar masses so electron degeneracy pressure can’t help o 2 things happen  (1) photodisintegration: high energy photons rip apart the nuclei in the core  atomic nuclei of iron in the core are now being blown apart  (2) electrons & protons are squeezed together under the enormous pressure of gravity to form a neutron & neutrino o net result: converted core of iron into a solid ball of neutrons o this creates a core of neutrons (like a giant nucleus)  a neutron star o this star has the mass of a massive star  a supernova explosion: collapse  rebo
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