6.6-8

Question 1

Interstellar Gas Dynamics

what physics is considered and what types of gases are there?

Answer 1

Complex physics including:

• dynamical processes
• radiation processes
• gravity

with different kinds of gases like:

• diffuse gas (cold, warm, and hot)
• dense gas (molecular clouds and HII regions)

quite random on one hand, but maybe also a good summary, idk

Question 2

Cooling and Heating Processes

Context: MW Galaxy

Answer 2

• Λ(T): Cooling increases strongly with T for T ≈ 100 K (CO lines) and T ≈ 10’000 K (nebular lines)
• Γ(r): Heating depends strongly on location relative to dominant radiation sources

Question 3

Thermal Equilibrium

when is it stable / unstable?

Answer 3

• cooling equals heating (L = Λ - Γ = 0)
• stable for ∂L/∂T > 0
• unstable for ∂L/∂T < 0

Question 4

Pressure Equilibrium

and values for different types of gas

Answer 4

Pressure equilibrium between different gas components is approximated by:

P_gas = n · k _B · T

• Diffuse gas: n · T ≈ 10^9±1 m^-3 K
• Dense gas: n · T ≈ 10^12±2 m^-3 K

Question 5

Jeans Mass

numerical examples

Answer 5

Jeans mass for equilibrium:
Mcloud(T,rho bar) prop to T^3/2 / rhobar^1/2

• HI cloud: ≈ 2 · 10⁴ M_⊙
• Molecular cloud: ≈ 2 M_⊙

M_cloud(T, rho_bar) = [(375/4π)^(1/2)] · [(k_B · T)/(G · m_H * mu)]^(3/2) · (1/rho_bar)^(1/2)

Question 6

Star Formation

is influenced by:

Answer 6

Star formation is influenced by:

• Gravitational equilibrium
• Angular momentum
• Magnetic fields
• Star formation feedback

Molecular clouds collapse due to these factors.

Question 7

Initial Mass Function

Answer 7

Stars are born with a universal mass distribution, described by:

dN_S/dM ∝ M^-2.35

for M > 0.5 M_⊙.

-> lower mass stars far more numerous

Question 8

Galactic Center Observations (3)

Answer 8

Observations of the Galactic center reveal:

• strong foreground dust extinction
• Central disk of HI and CO gas
• Supermassive black hole.

Question 9

Size of a Black Hole

Answer 9

Schwarzschild Radius (r_S) for a black hole is estimated by:

r_S = 2 · G · M / c²

(Size depends on the black hole’s mass.)