Chapter 21/22: Birth of Stars and Low Mass Star Evolution Flashcards
What is fragmentation?
When molecular stars contract (due to shock or pressure) into smaller pieces forming tens or hundreds of individual stars.
What do stars form in?
Clusters.
What is a cloud collapse?
When the core collapses the self-gravity grows stronger and then the collapse speeds up (inside out)
What is a Protostar
Center of the accretion disk
What is an accretion disk?
Material that falls inward in a collapsing molecular cloud core that accumulates in a flat, rotating accretion disk.
What does the core gradually reach?
1 million K
What is a protostar always in?
Hydrostatic Equilibrium
What is bipolar outflow?
Material that falls into a star, other material is blown away.
When the outflow is organized and moves quickly what are they?
bipolar jets.
What is a T Tauri Star?
Low-mass protostars
What are Herbig Ae/Be stars?
Higher-mass protostars
What is heated by the formation of stars nearby?
Emission nebulae
What is a protostar’s first appearance on the HR diagram?
Red Giant
In the next stage of a protostar on the HR diagram…
The luminosity drops a lot and so does the temp until its in the main sequence.
Stars don’t what?
Move along the Main Sequence because once they are there they reach equilibrium until their fuel runs out.
What is the Hayashi Track?
Pre-main sequence evolution on the HR diagram. (Star remains same color)
What happens to the stars energy?
The core runs out of H and stops producing energy (now off the main sequence) and helium begins to accumualte.
What makes the core contract?
The fuel is used up so less radiation pressure is produced.
What happens when hydrogen in a shell around the core heats?
it begins to duse to form Helium and now burns hotter than before and pushes out (into Red Giant)
What is Helium Fusion in the Red Giant?
Once the core reaches 100,000,000 K it starts to fuse in a “helium flash” through the triple-alpha process.
What is the triple-alpha process?
3 Helium nuclei fuse to form carbon (Beryllium is produced briefly).
What is a planetary nebula?
As the dead core of the star cools, it expands and dissipates into its surroundings (clouds of light) (lasts for 50,000 years)
What is a white dwarf?
Once the nebula is gone the core is extremely hot and dense and small.
