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RRY041 > 1. Introduction > Flashcards

1. Introduction Flashcards

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

A

About 40%

20
Q

Cold neutral medium (CNM) synonym

A

Cool HI

21
Q

Temperature of cool HI

A

100 K

22
Q

Which is more dense, warm or cool HI?

A

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

23
Q

Diffuse molecular gas

A

Dense HI gas

24
Q

Dense molecular gas

A

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

25
Q

Cosmic microwave background temperature

A

2.725 K

26
Q

Is the ISM in thermal equilibrium?

A

No, far from it!

27
Q

Why are short wavelength observations usually done on high altitude or in space whilst radio astronomy isn’t?

A

Because of atmospheric interference for higher frequencies

28
Q

What are the four phases (or astronomical classifications) of a baryon?

A

IGM, ISM, Star, Stellar remnant

29
Q

Largest part of stellar ejecta

A

Planetary nebulae (0.3-1 solar mass per year of a total of 1 solar mass per year ejecta in the Milky Way)

30
Q

Can ISM become IGM?

A

Yes, but only through galactic wind or strong emissions from quasars and similarly which is very unlikely

31
Q

How great is the infall (IGM –> ISM) in the Milky Way?

A

Less than one solar mass per year

32
Q

Where do ISM energy come from?

A

Stars (photon and ejecta), Extragalactic background photons and Self-gravity (contraction)

33
Q

What happens to the ISM energy?

A

It leaves the galaxy to the cold sky through radiative cooling

34
Q

How is the coronal gas ionized?

A

Collisionally

35
Q

Energy of a photoionization photon

A

13.6 eV (912Å)

36
Q

Energy density CMB

A

0.25 eV cm^-3

37
Q

Three energy densities are hydrodynamically coupled, which?

A

Thermal (3P/2), Hydro (rhov^2/2), Magnetic (B^2/8pi)

38
Q

Energy density of starlight in local ISM

A

0.5 eV cm^-3

39
Q

Is CMB energy density coupled to any other energy density?

A

No

40
Q

In what process do Coronal Gas transform into HII?

A

In Radiative Cooling

41
Q

Through what process do HII transform into HI?

A

Radiative Recombination

42
Q

Is HI in pressure equilibrium with ISM?

A

Yes, it is

43
Q

Is H2 in pressure equilibrium with ISM?

A

Yes, it is in pressure equilibrium with ISM

44
Q

Temperature of diffuse H_2

A

60 K

45
Q

What is the common cooling procedure for HI, Diffuse H_2, Dense H_2 and Cool stellar outflows/winds?

A

FIR-emission (Far InfraRed)

46
Q

Thermal energy in terms of pressure

A

U_thermal = 3*p/2

47
Q

In the study of collisional processes, what is capital Lambda?

A

It is the Debye length L_D divided by the minimum impact parameter b_min

RRY041 (21 decks)

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