Section 7: Stellar evolution, Hertzsprung-Russell diagram

Question 1

What is the condition for expansion in a star?

Answer 1

2U>|Ω|

Question 2

What is the condition for cloud collapsing in a star?

Answer 2

2U<|Ω|

Question 3

What is the equation for collapse for a star?

Answer 3

3Nk_BT<3/5 GM²/R

Question 4

What is a protostar?

Answer 4

The end result of cloud collapsing and is pre main sequence

Question 5

What happens after the formation of the protostar?

Answer 5

Star adapts to thermal energy
Outer regions have to lose heat to be able to collapse

Question 6

What occurs during the main sequence lifetime of a star?

Answer 6

Hydrogen burning, PP chain
Over time Helium builds up in the core

Question 7

What is the gravitational energy for star formation?

Answer 7

Ω=-3/5 GM²/R

Question 8

What is the scaling law for low mass stars?

Answer 8

L α μ⁷M⁵

Question 9

What is a star cluster?

Answer 9

A group of stars formed from the same molecular cloud

Question 10

What are the properties of a star cluster?

Answer 10

Same age
Same composition
Same distance

Question 11

What happens to stars on the subgiant branch?

Answer 11

Hydrogen in the core has been exhausted
Core grows until thermal pressure can no longer support it
Core is inert and has no fusion (L=0)
Core contracts and becomes degenerate

Question 12

What happens to stars on the red giant branch?

Answer 12

Core contracts from increased mass
Envelope expands
Temperature increases the luminosity increases
Star gets hot enough for Helium fusion

Question 13

What is the Helium flash?

Answer 13

Core is degenerate
Helium fusion to carbon and oxygen
Energy release mostly absorbed by outer layers of the star
Ends when degeneracy is lifted

Question 14

What is the horizontal branch?

Answer 14

Helium burning to carbon and oxygen
Hydrogen burning in shell

Question 15

What is the asymptotic giant branch?

Answer 15

Helium is exhausted in the core
Burning of He in shell and H in outer shells

Question 16

What happens post the AGB?

Answer 16

Planetary nebula from ejected material
Expand hot carbon and oxygen core
White dwarf, M~0.6M_sun, R~R_E

Question 17

At what mass do white dwarfs collapse?

Answer 17

M~1.4M_sun
Supernovae
Gravitational collapse

Question 18

What is the range for higher mass stars?

Answer 18

M>8M_sun

Question 19

What is the ends result for stars with M<25M_sun

Answer 19

Neutron star supported by degeneracy pressure
Maximum mass M~3M_sun
Typical mass M~1.4M_sun