Astro 103 - Lecture 13

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END GAME I: EXPLOSION


1. Fundamental Particle Zoo


Two particle families:

  • leptons - fundamental particles
  • hadrons - made up of quarks.

- 3 `generations' of leptons
- 3 `generations' of quarks (never a ``naked'' quark!)
- generations differ in mass



Consequences for increasingly degenerate matter:

Recall: mass and energy are convertible (E=mc2)

Eventually ``Fermi energy'' exceeds energy difference between mass of two particles

Easier for new particles to be created



2. High Mass Stellar Evolution


Short lives

Heavy element production in ``onion skin'' layers of star

- off the Main Sequence

The most massive stars ``burn'' up to iron in the core

Iron is the ``limit'' for exothermic fusion

- i.e., iron cannot fuse with anything to produce energy

- iron nuclei are the most stable of heavy elements


So what happens after the iron core is formed ?


uh oh ...



3. Core Collapse


. . . beyond white dwarf densities


Here's the scenario:


a.  Collapse heats core

b.  Nuclei are broken apart n, p+

+ all the e- already there

= hot, dense particle soup

c.  electrons (e-) more and more degenerate

d.  protons (p+) and neutrons (n) also degenerate,

- but not as much as e-:

``Fermi Sea'' isn't as high

Why: They (p+, n) are not fundamental particles

More states per given energy level

Click here for how to "picture" the ``Fermi Seas''!

e.  Electron ``Fermi Energy'' high enough for e- to form heavier particles:

e- + p+ n +

`` inverse beta decay ''

f.  e- degeneracy decreases

g.  n degeneracy increases

h.  collapse comes to ``screeching'' halt

i.  core bounces

j.  shock wave rips apart outer layers of star


Super-nova explosion (Type II)



4. Super novae types


Two types:

Type I

observed: Hydrogen poor

white-dwarfs ``over the limit'' (mass limit)

explosive Carbon fusion in core

``Carbon Flash'' - a deflagration

entire star is ripped apart

Type II

observed: Hydrogen rich

massive stars with iron cores

core bounce

formation of a neutron star


Type I mass limit: white dwarf ``critical mass''

Nobel prize winner

Over this mass, white-dwarf core collapses;

electron degeneracy pressure overwhelmed by gravity.



5. Other stellar explosions: Binaries and Mass Transfer - stellar thieves!


Mass from one star gravitationally 'stolen' by companion:

When Companion is . . . Produces . . .
on the Main Sequence blue straggler
low-mass white dwarf "nova"
critical-mass white dwarf "super-nova" (Type I)
neutron star X-ray burst (???)
black hole X-ray or Gamma-ray burst (???)

Nova:

surface-fusion of Hydrogen on a white dwarf

(non-destructive for white dwarf)

Super-nova:

catastrophic explosion


Nova vs. Super-nova:

- different light curves

- different amounts of energy released



Q13.1 How does the increase of electron degeneracy in a collapsing iron core lead to the formation of a neutron star?

(a) the electron Fermi Energy becomes high enough for electrons and protons to form neutrons

(b) the neutron Fermi Sea compresses the electrons into the protons

(c) degeneracy is a state where one particle transforms into another particle

(d) the iron nuclei in the core interact with the electrons, and transform them into neutrons

(e) as the iron nuclei are ripped apart, this forces the electrons to become more degenerate


Q13.2 What is the same for Type I and Type II supernovae?

(a) stellar progenitors

(b) composition

(c) light curves

(d) remnants

(e) brighter than a nova


Lectures Lecture page Astro103 page
Last updated: Aug 23, 2011 Matthew A. Bershady