PHYS 183 Lecture Notes - Electron Degeneracy Pressure, Degenerate Matter, Photodisintegration

10 views2 pages
17 Mar 2013
PHYS 183 The Milky Way Inside and Out Tracy Webb Winter 2013
Lecture 25: March 15th, 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
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 rebound outer layers lost
o core collapse is halted with neutron degeneracy pressure kicks in
can only squeeze neutrons together so close until they start to react
o core overshoots & rebounds slams into infalling outer layers & is stalled
o but second wave of neutrinos catches up & initiates second shockwave
o all of this happens in less than a second
o this results in a pulsar
o can’t predict when and where this will happen
o it is possible to have too much mass so neutrons can’t support core never collapses so
results in neutron star of blackholes
nucelosynthesis during the explosion
o elements heavier than iron require energy
o this energy is supplied by the supernova explosion (store energy in the core)
o make all elements more massive than iron in supernova explosions this makes them
rare since this is the only source of them that we know & supernova explosions open
happen in high mass stars which are rare themselves
just how bright is it? brighter than a galaxy
neutron stars are supported by neutron degeneracy pressure (8-12 solar masses)
o take the size of the sun and squeeze it down to the size of Manhattan or Montreal
extremely dense
Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

Get access

$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
Booster Classes
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
Booster Classes