Chapter 16  Stellar Birth

 

What is this?

 

Birth

 Stellar nurseries  Scorpius

Interstellar Medium ISM

Mostly H and He but others and dust also

Giant Molecular Clouds

Dust absorbs and reddens light

 

Star formation

       Requirements: cold 10-30K and ‘dense’ 105 atoms/cm3

       

       Collapse

magnetic fields help slow collapse

 

 Fragmentation

 

Shrouded inside the cloud but can be seen in IR

 

globules

 

In the early Universe almost no molecules (except H2) or dust

Large isolated stars formed of just H and He

 

Protostar

Energy source is gravity

Stabilized by pressure from trapped heat

If you don't have angular momentum you fall inward

 

If you do have angular momentum you can form a disk

       Disks 1 2 3

       Jets T Tauri stars and Herbig-Haro Objects

       Winds clear out dust

 

 

Evolutionary tracks

protostar infall

convective contraction

radiative contraction

FUSION

low mass  high mass

 

Limits on the mass

Below .08MSun Fusion never starts

 

Stopped by degeneracy

Brown Dwarfs  also called L and T dwarfs

Numerous but hard to detect

 

Nothing over 200MSun (except in the early universe)

stopped by radiation pressure

 

It is easier to make a low mass star than a high mass star