Chapter 21/22: Birth of Stars and Low Mass Star Evolution

Question 1

What is fragmentation?

Answer 1

When molecular stars contract (due to shock or pressure) into smaller pieces forming tens or hundreds of individual stars.

Question 2

What do stars form in?

Answer 2

Clusters.

Question 3

What is a cloud collapse?

Answer 3

When the core collapses the self-gravity grows stronger and then the collapse speeds up (inside out)

Question 4

What is a Protostar

Answer 4

Center of the accretion disk

Question 5

What is an accretion disk?

Answer 5

Material that falls inward in a collapsing molecular cloud core that accumulates in a flat, rotating accretion disk.

Question 6

What does the core gradually reach?

Answer 6

1 million K

Question 7

What is a protostar always in?

Answer 7

Hydrostatic Equilibrium

Question 8

What is bipolar outflow?

Answer 8

Material that falls into a star, other material is blown away.

Question 9

When the outflow is organized and moves quickly what are they?

Answer 9

bipolar jets.

Question 10

What is a T Tauri Star?

Answer 10

Low-mass protostars

Question 11

What are Herbig Ae/Be stars?

Answer 11

Higher-mass protostars

Question 12

What is heated by the formation of stars nearby?

Answer 12

Emission nebulae

Question 13

What is a protostar’s first appearance on the HR diagram?

Answer 13

Red Giant

Question 14

In the next stage of a protostar on the HR diagram…

Answer 14

The luminosity drops a lot and so does the temp until its in the main sequence.

Question 15

Stars don’t what?

Answer 15

Move along the Main Sequence because once they are there they reach equilibrium until their fuel runs out.

Question 16

What is the Hayashi Track?

Answer 16

Pre-main sequence evolution on the HR diagram. (Star remains same color)

Question 17

What happens to the stars energy?

Answer 17

The core runs out of H and stops producing energy (now off the main sequence) and helium begins to accumualte.

Question 18

What makes the core contract?

Answer 18

The fuel is used up so less radiation pressure is produced.

Question 19

What happens when hydrogen in a shell around the core heats?

Answer 19

it begins to duse to form Helium and now burns hotter than before and pushes out (into Red Giant)

Question 20

What is Helium Fusion in the Red Giant?

Answer 20

Once the core reaches 100,000,000 K it starts to fuse in a “helium flash” through the triple-alpha process.

Question 21

What is the triple-alpha process?

Answer 21

3 Helium nuclei fuse to form carbon (Beryllium is produced briefly).

Question 22

What is a planetary nebula?

Answer 22

As the dead core of the star cools, it expands and dissipates into its surroundings (clouds of light) (lasts for 50,000 years)

Question 23

What is a white dwarf?

Answer 23

Once the nebula is gone the core is extremely hot and dense and small.