<-that's a molecular
cloud.
Molecular cloud: mass ~100 Msun, r~10,000 AU, composition~ cosmic abundance (from spectroscopy)
Gravitational collapse - free-fall time ~ 1 Million years. (Triggered by super nova? evidence from condules (see book) but see [1] below.)
Central star nuclear fusion starts - heats up.
Conservation of angular momentum -> adding up of small eddies in original cloud to single direction spin which increases as the cloud shrinks.
[An interesting cautionary note from a book on stellar structure about our lack of understanding about how to deal with the issue of how the Sun (and similar stars) lost its angular momentum as it formed from the collapsing nebula (from Hansen & Kawaler, Stellar Interiors, Springer-Verlag, 1994) ]
Collisions / friction -> disk collisions -> disk - it is collisions, not gravity, that causes the cloud to form a disk as it collapses - just as in making galaxies and ring systems. Another cartoon.
Polar wind -> loss of Sun's angular momentum (also magnetic braking).
Viscous drag = friction -> disk collapse, heating up - temperature in the solar nebula disk
Timescale ~ 30 million years
<- like Beta-pictoris
and all those Proplyds in previous class
Hydrostatic Equilibrium
Shape of the disk - its thickness and variations with radiao distance - can largely be explained by the principle of hydrostatic equilibrium where the gravity force is balance by the pressure gradient of the gas in the nebula. See derivation of width of disk part 1 and part 2 - and pages 104-105.
Disk COOLs (->temperature gradient) by radiation (IR - that's how we see such disks in IR as Proplyds). The archetypical place to watch this happen is in the Orion nebula - see a map of where this is in the relation to us in the Galaxy.
Condensation: gas -> solid [Reference discussing evidence of earliest building-blocks of the solar system}
Accretion: pieces stick together - Big mystery part of solar system formation - HOW? collisional timescales for accretion are too long - what makes them STICK together? (Fran's guess=Organic "goo"???)
Once grains -> pebbles -> boulders - then it becomes easier -> kilometer -> planets
Kilometer+ objects are called PLANETESIMALS. These formed the cores of the giant planets.
At some point - after main planets formed - the solar system was cleared of gas - the nebula was blown away - HOW? Well, star- and planet-forming regions have some young stars which have very strong solar winds - e.g. a star called T-Taurus - hence, this process is called the "T-Tauri phase" of solar system formation.