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RRY041 > 1. Introduction > Flashcards

1. Introduction Flashcards

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1
Q

Ions and electrons with kinetic energies far greater than thermal, often extremely relativistic – energies as high as 10^21 eV have been detected.

A

Cosmic rays

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2
Q

1 Gauss

A

10^-4 Tesla

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3
Q

Thickness of the Milky Way

A

500 pc

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4
Q

Distance between sun and galactic center

A

8.5 kpc

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5
Q

Mass of Milky Way

A

10^11 solar masses

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6
Q

Half thickness

A

Distance above (or below) midplane where density has dropped by 50%

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7
Q

Most common type of gas in the Milky Way galaxy

A

HI (60%)

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8
Q

Hot Ionized Medium (HIM) in another name

A

Coronal gas

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9
Q

Coronal gas temperature

A

500 000 K

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10
Q

HII region

A

Ionized hydrogen in a dense volume near a dense cloud

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11
Q

HII gas

A

Gas where the hydrogen has been photoionized by ultraviolet photons from hot stars

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12
Q

Diffuse HII

A

Intercloud medium of HII gas with lower density

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13
Q

Warm ionized medium (WIM)

A

Extended low density diffuse HII

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14
Q

Type of gas in a planetary nebula

A

HII gas

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15
Q

Mass of stars creating planetary nebulae

A

0.8 - 6 solar masses

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16
Q

Lifetime of planetary nebulae

A

10 000 yr

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17
Q

Warm neutral medium (WNM) synonym

A

Warm HI

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18
Q

Temperature of warm HI

A

5000 K

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19
Q

Warm HI fills how much of the volume of the disk

20
Q

Cold neutral medium (CNM) synonym

21
Q

Temperature of cool HI

22
Q

Which is more dense, warm or cool HI?

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A

Cool (30 cm^-3 vs 0.6 cm^-3)

23
Q

Diffuse molecular gas

24
Q

Dense molecular gas

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A

Gravitationally bound gas (10^3 cm^-3)

25
Cosmic microwave background temperature
2.725 K
26
Is the ISM in thermal equilibrium?
No, far from it!
27
Why are short wavelength observations usually done on high altitude or in space whilst radio astronomy isn't?
Because of atmospheric interference for higher frequencies
28
What are the four phases (or astronomical classifications) of a baryon?
IGM, ISM, Star, Stellar remnant
29
Largest part of stellar ejecta
Planetary nebulae (0.3-1 solar mass per year of a total of 1 solar mass per year ejecta in the Milky Way)
30
Can ISM become IGM?
Yes, but only through galactic wind or strong emissions from quasars and similarly which is very unlikely
31
How great is the infall (IGM --> ISM) in the Milky Way?
Less than one solar mass per year
32
Where do ISM energy come from?
Stars (photon and ejecta), Extragalactic background photons and Self-gravity (contraction)
33
What happens to the ISM energy?
It leaves the galaxy to the cold sky through radiative cooling
34
How is the coronal gas ionized?
Collisionally
35
Energy of a photoionization photon
13.6 eV (912Å)
36
Energy density CMB
0.25 eV cm^-3
37
Three energy densities are hydrodynamically coupled, which?
Thermal (3P/2), Hydro (rho*v^2/2), Magnetic (B^2/8*pi)
38
Energy density of starlight in local ISM
0.5 eV cm^-3
39
Is CMB energy density coupled to any other energy density?
No
40
In what process do Coronal Gas transform into HII?
In Radiative Cooling
41
Through what process do HII transform into HI?
Radiative Recombination
42
Is HI in pressure equilibrium with ISM?
Yes, it is
43
Is H2 in pressure equilibrium with ISM?
Yes, it is in pressure equilibrium with ISM
44
Temperature of diffuse H_2
60 K
45
What is the common cooling procedure for HI, Diffuse H_2, Dense H_2 and Cool stellar outflows/winds?
FIR-emission (Far InfraRed)
46
Thermal energy in terms of pressure
U_thermal = 3*p/2
47
In the study of collisional processes, what is capital Lambda?
It is the Debye length L_D divided by the minimum impact parameter b_min

RRY041 (21 decks)

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