D.4 Stellar Processes (HL)

D.4 Stellar processes

	Type 1a Supernovae	Type 2 Supernovae
Formation	Core produced when mass from a companion star accretes onto a white dwarf, forcing it to exceed the chandrasekhor limit (1.4M~sun~) [EP吸不住，吸过来的东西立刻进行fusion]	Produced when a massive red supergiant stars explodes - Core collapse - Implosion is opposed by neutron degeneracy pressure that causes an outward shock wave
	Do not active hydrogen lines in their spectra (But carbon, oxygen, silicon, iron)	Have hydrogen line
	Have a luminosity which falls off sharply after explosion	Luminosity falls off gently after the explosion [有段平台期，有点像晶体结构的热量变化的线]

Interstellar gas cloud (nebula) from earlier supernova
gravitational attraction between particles
Jeans criterion
- The magnitude of the gravitational potential energy of the cloud must be greater than the total random kinetic energy of the particles of the cloud.
- If the mass of cloud is greater than the Jeans' mass M~j~ for a particular redius and temperature, the interstellarr gas collapse/coalesces
As gas collapse, temperature increases leading to nuclear fusion
- Protostar: when the temperature rises sufficiently for visible light to be emitted

Main sequence stars:
- Proton-proton cycle
  - Net effect: $4^{1}_{1}H \rightarrow$ $^4_2He$ + 2 positron + 2 electron neutrino
For stars more massive than M~sun~
- CNO cycle

T与M^-2.5^ 成比例(T是寿命)

$$ \frac{T}{T_{\bigodot}}=(\frac{M}{M_{\bigodot}})^{-2.5} $$

Layered structure of massive start

The elements arrage themselves in layers, haviest at the cave, lightest in the envelope.
Nuclear fusion produce ever heavier elements depending on the mass of the star

Fusion cannot produce elements heavier than iron

Binding energy per nucleon peaks near iron => one of the most stable elements (Ni-62)
Formation of heavier elements than iron is not energetically possible.

To produce the heavier elements than iron.

S-process	R-process
Slow neutron capture	Rapid neutron capture
Small number of neutrons are produced in fusion
Have enough time to undergo beta decay before further neutron capture	Further neutron are captured before the beta decay
Ends with the production of bismuth-209	Can form nuclides heavier than bismuth-209