PHYS 182 Lecture Notes - Lecture 18: Protogalaxy, Red, Isotropy
PHYS182: Our Evolving Universe
2017-11-09 LEC 18
Star-Gas-Star Cycle
- Planetary nebula or supernova: a lot of
the material in the star cores gets swept out
into interstellar space
- Hot bubbles = hot nebula
o The heat comes from the initial
stars, but then the heat escapes
- The clouds cool and you get atomic
hydrogen clouds
- In molecular clouds, gravity pulls things
together and you get a new generation of
stars
- When the first stars formed there was only
H and He, no C
o Heavier elements are formed in
the core, and then ejected in
subsequent explosions
- The next generations of star formation after
the first had heavier elements
Planetary Nebula
- End stage of a low mass star
o White dwarf formed, outer layers ejected, and you get a planetary nebula
- In low mass stars, recall there is no C burned into Fe
- Crab nebula: a supernova remnant
o if you take a spectrum you should be able to see an iron line
- To determine whether something is a planetary nebula or a supernova remnant, you take the
spectrum
Planetary Nebula Spectrum
- This is a hot gas emitting radiation, which gives you emission lines
CasA supernova Remnant Spectrum
- See Iron, Calcium, Magnesium à know it is a high mass star
remnant
Atomic H Cloud
- Still gives off some energy (still contains all of the other elements)
- The nebulae have cooled and you are left with clouds of atomic H
- When the cloud cools further, you get a cold molecular H cloud
o The spectrum is different at this point because the spectral
lines of molecules are differen
Document Summary
Planetary nebula or supernova: a lot of the material in the star cores gets swept out into interstellar space. Hot bubbles = hot nebula: the heat comes from the initial stars, but then the heat escapes. The clouds cool and you get atomic hydrogen clouds. In molecular clouds, gravity pulls things together and you get a new generation of stars. When the first stars formed there was only. H and he, no c: heavier elements are formed in the core, and then ejected in subsequent explosions. The next generations of star formation after the first had heavier elements. End stage of a low mass star: white dwarf formed, outer layers ejected, and you get a planetary nebula. In low mass stars, recall there is no c burned into fe. Crab nebula: a supernova remnant if you take a spectrum you should be able to see an iron line.
