Section 6 - Energy generation in Stars

Question 1

What is the virial theorem?

Answer 1

Relates thermal and gravitational potential by
Ω=-2U

Question 2

How do the gravitaional energy and pressure balance out?

Answer 2

Ω=-3P

Question 3

What is the thermal energy per particle?

Answer 3

U=3/2 k_BT

Question 4

What is the pressure equation of state?

Answer 4

P=nk_BT

Question 5

What is the self-regulation of a star for increasing E?

Answer 5

If E increases Ω increases and the star expands
U decreases and the temperature drops and fusion decreases

Question 6

What is the self-regulation of a star for decreasing E?

Answer 6

If E decreases Ω decreases and the star shrinks
U increases and the temperature rises and fusion increases

Question 7

What is the timescale of a star?

Answer 7

t=quantity/rate of change

Question 8

What is the escape velocity?

Answer 8

V_escape=sqrt(2GM/R)

Question 9

What is the gravitational timescale?

Answer 9

τ=R_*/V_escape
Relevant for supernovae

Question 10

What is the thermal timescale?

Answer 10

τ=U/L=GM²/2RL
Relevant for stars collapsing during formation

Question 11

What is the nuclear timescale?

Answer 11

τ=ηχm_cc²/L

Question 12

What are the conserved quantities in a reaction?

Answer 12

Electric charge
No of nucleons
No of leptons
Momentum and energy

Question 13

What is the most common fusion in the Sun?

Answer 13

PP1 chain

Question 14

What is the PP1 chain?

Answer 14

4 Hydrogen–>Helium+2 positrons + 2 neutrinos + 2 gamma rays

Question 15

What determines the reaction rate?

Answer 15

The duration of the slowest process
(Proton to neutron for PP1)

Question 16

What is the reaction rate for fusion in the Sun?

Answer 16

Once per 10¹⁰ years for a given proton