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Physics 107 > Final Exam Short Answers > Flashcards

Final Exam Short Answers Flashcards

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1
Q

How old are Bright Stars in the Arms of a Spiral Galaxy?

A

Young.

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2
Q

Why don’t Spiral Galaxies ‘Wind Up’?

A

Outer parts orbit more slowly.

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3
Q

What is Important to Remember about Elliptical Galaxies?

A

No ongoing star formation - red and dead.

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4
Q

What Type of Galaxy is the Most Massive?

A

Elliptical.

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5
Q

What Causes Irregular Galaxies?

A

Disturbed by interactions with larger galaxies.

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6
Q

What are Active Galaxies?

A

Galaxies that generate energy at their cores.

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7
Q

What will Eventually Happen to all Galaxies in the Universe with no more Star Formation?

A

Only small, old stars left as part of elliptical galaxies.

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8
Q

How do Old Stars Return Gas to Interstellar Medium?

A

By supernova explosion or stellar winds.

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9
Q

Which Galaxies Form First and How?

A

Small galaxies form first and larger galaxies form from mergers.

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10
Q

What are the 2 Kinds of Matter?

A

Dust and Radiation.

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11
Q

What are the 3 Key Characteristics of Dust?

A

Not moving, no pressure, stars and galaxies.

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12
Q

What are the 3 Key Characteristics of Radiation?

A

Light speed, high pressure, redshifts with expansion.

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13
Q

How does Matter Progress with Heat?

A

Solid, liquid, gas, plasma, npe, quarks, ???

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14
Q

What Happened 10^-6 Seconds After the Big Bang?

A

Quark-hadron phase transition.

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15
Q

What does the Ratio of Protons to Neutrons depend on?

A

Temperature.

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16
Q

How do we Know Photon-Number Density?

A

Due to temp of CMB.

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17
Q

When did Primordial Nucleosynthesis Take Place?

A

First 3 minutes after the big bang.

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18
Q

Why did the Universe have to Cool Before Atoms could be Made?

A

Photons were too energetic - would make ions.

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19
Q

What was Recombination?

A

Universe cooling enough for H atoms to be stable, universe now transparent 380,000 years after big bang.

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20
Q

Who Discovered the Microwave Background?

A

Wilson and Penzias.

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21
Q

How was Microwave Background Discovered?

A

Accidentally using a satellite communications device.

22
Q

What is the Temperature of the Microwave Background?

A

3 Degrees Kelvin.

23
Q

What Happens to Photon Energy as the Universe Cools?

A

It drops.

24
Q

What is the Ratio of Neutrons to Protons at Freeze Out?

A

1N : 7P.

25
Q

What Happens to the Universe’s Temperature as it Expands?

A

It cools down.

26
Q

How has the Composition of the Universe Changed?

A

Now: matter and dark energy
Then: radiation and particle physics

27
Q

Who discovered Uranus?

A

William Herschel in 1781.

28
Q

When was the Great Debate?

A

1920s.

29
Q

When were the Rules of General Relativity Implemented?

A

1915.

30
Q

How does Orbital Period Relate to Radius?

A

Year is proportional to radius ^1.5.

31
Q

Why do Inner Planets Move Faster?

A

Speed is proportional to distance ^0.5.

32
Q

Who Discovered Spiral Galaxies Move too Fast?

A

Vera Rubin (1975-80).

33
Q

What are all Galaxies Embedded in?

A

A dark halo - 80% of its total mass.

34
Q

Where do Galaxies Live?

A

In clusters and superclusters.

35
Q

Why do Galaxies Cluster?

A

Dark matter - too many for chance gatherings, lots of “missing mass”.

36
Q

What is Gravitational Lensing?

A

Light bent by gravity, distant images distorted.

37
Q

What is Dark Matter Likely to be?

A

A fundamental particle.

38
Q

Why can’t we Detect Dark Matter?

A

We are transparent to it and it is transparent to us.

39
Q

What is the Hubble Flow?

A

Bound objects don’t expand.

40
Q

What is Hubble’s Constant Roughly?

A

66.93.

41
Q

How is Hubble’s Constant Measured?

A

Start with cepheids - measure close ones with parallax, or use supernovae.

42
Q

What are Supernovae?

A

Exploding stars: briefly outshine an entire galaxy.

43
Q

What are the 2 Types of Supernovae?

A

Type 2: Giant collapsing stars

Type 1a: Accreting white dwarf in a binary system.

44
Q

What is the Chandrasekhar Limit?

A

Max mass of a white dwarf.

45
Q

What does the Slope of Hubble’s Constant Line Tell us?

A

Hubble’s constant.

46
Q

What does the Shape of Hubble’s Constant Line Tell us?

A

How to constant changes.

47
Q

What Happens to Matter every time the Universe Doubles in Size?

A

Matter density drops by a factor of eight.

48
Q

What will happen to our Local Universe in the Future?

A

Dark energy increases, Hubble’s constant stabilises, galaxies spread out (apparent motion speeds up), distant galaxies move faster than light, so only local group is visible.

49
Q

When will M31 Merge with the Milky Way?

A

4 billion years.

50
Q

What is Concordance Cosmology?

A

Big questions about nature and origin of dark sector.

51
Q

How does Dark Energy Change as the Universe Expands?

A

Density doesn’t change.

52
Q

What are the Basic Ingredients of the Universe?

A

Dark matter, dark energy, radiation, atoms (baryons) with a neutrino background.

Physics 107 (7 decks)

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