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Astronomy GCSE > Cosmology > Flashcards

Cosmology Flashcards

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1
Q

What is the Doppler Effect?

A

The change in frequency of a wave caused by relative motion between the source of waves and the observer.

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2
Q

Is the Doppler Effect visible with any wave, or just visible light?

A

Any wave - including sound and all of the Electromagnetic spectrum.

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3
Q

Who discovered the Doppler Effect, and when?

A

Austrian physicist Christian Doppler, in 1842.

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4
Q

How did Hubble contribute to the discovery of the Doppler Effect?

A

Hubble and his assistant Milton Humason studied the spectra of almost 50 galaxies during the 1920s. They used the 100-inch Hooker telescope on Mt. Wilson in California.

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5
Q

How do you measure redshift?

A

Measure known wavelength in a lab.

Measure the corresponding wavelength from the source.

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6
Q

What happens to the spectra lines when something is redshifted?

A

The absorption lines will move toward the red end of the spectrum.

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7
Q

What does it mean when something has high redshift?

A

It is far away

It is moving very quickly away from us.

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8
Q

What equation is used to determine recession velocity?

A

(λ- λ0)/λ0=v/c

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9
Q

Which galaxy in the local group has blueshift?

A

The Andromeda Galaxy, which will collide with us in 3.75 billion years.

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10
Q

What are quasars?

A

Distant galaxies with high redshifts.
Compact appearance makes them look like stars.
Have high luminosities.
Have jets.
Emit everything, but particularly X-rays and radio waves.

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11
Q

Describe the discovery of quasars.

A

Discovered 1963 by radio astronomers.
Source 3C 48 in 1960 was mapped to a bright blue ‘star’ and its spectrum was obtained, which had many broad emission lines.
Source 3C 273 was mapped in 1962 due to lunar occultation to a locational counterpart. This was determined by Cyril Hazard and John Bolton at Parkes Radio Observatory in Australia.
Martin Schmidt, an astronomer, could then determine its spectrum using the 200-inch Hale telescope on Mt.Palomar in California.
Schmidt noticed strange emission lines (highly red-shifted lines of hydrogen).
Schmidt calculated recession velocity at 47,000km/s.
Several other sources were found to have extremely large redshifts.
New group of active galaxies, quasars, was made.

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12
Q

What is Hubble’s Law?

A

Distance is proportional to recession velocity.

v=Hd

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13
Q

What is the value of the Hubble constant?

A

77 km/s/Mpc

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14
Q

Hubble’s constant has an uncertainty of:

A

15%

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15
Q

How do astronomers use the Hubble constant to determine the age of the universe in years?

A

Convert the constant into units of /second.
Invert H.
Convert from seconds to years.

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16
Q

What is the age of the universe?

A

14 billion years

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17
Q

What is CMB radiation?

A

Background microwave radiation that can be detected coming from every direction.

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18
Q

How did CMB come about?

A

When the universe first formed, it was hotter, denser and filled with a background glow from a plasma of hydrogen.
When the universe expanded, both the plasma and radiation cooled.
Due to the development of atoms, the universe became transparent.
This allowed the radiation to continue and stretch.
This stretching has increased its wavelength to that of microwaves.
It also means that it has cooled to a temerature of 2.7K.

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19
Q

Why is CMB ‘almost’ uniform?

A

When the universe was at its beginning, it was uniformly hot.

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20
Q

Why is CMB significant for the Big Bang?

A

It has a temperature of 2.7K, which matches the idea that because the universe has expanded, it has cooled.
It has a wavelength of microwaves, which matches the idea that the radiation has expanded with the universe.

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21
Q

How was CMB discovered?

A

George Gamow in 1948 predicting that the universe must have cooled to 5K if the original universe had been extremely hot and dense.
It was discovered in 1965 by Arno Penzias and Robert Wilson.
The discovery was an accident.
They intended to detect faint radio waves from the Echo balloon satellites at the Bell Laboratories in Homdel, New Jersey.
They discovered a weak noise day and night coming from every direction - despite eliminating all souces of external interference.
They contacted a team of astrophysicists from the nearby Princeton University led by Robert Dicke, who had been looking for this noise.
Penzias and Wilson won Nobel prize for physics in 1978.

22
Q

What conditions did Penzias and Wilson discover CMB under?

A

They had eliminated all other sources of radio interference.
It was coming from all directions.
It was far stronger than they expected.
It was apparent day and night.

23
Q

When was COBE launched, and by who?

A

By NASA in 1989.

24
Q

What did COBE confirm?

A

The isotropy of CMB on a large scale, but small ripples on a small scale, due to different densities of materials.

25
Q

Why was COBE significant?

A

It allowed the study of the distribution of matter and energy in the early universe.
Alluded to how galaxies would form due to ripples.

26
Q

When was WMAP launched, and by who?

A

NASA in 2001.

27
Q

What did WMAP do?

A

Studied CMB in more detail.

28
Q

Why was WMAP significant?

A

Confirmed existence of dark energy.
Enabled cosmologists to estimate the contribution of dark matter in the universe.
Helped astronomers refine their models of the composition and evolution of the early universe, and age of the universe.

29
Q

When was Planck launched, and by who?

A

NASA in 2009.

30
Q

What is dark matter?

A

Matter that does not reflect any form of electromagnetic radiation, but composes 95% of the universe’s mass and thus has noticeable gravitational effects.

31
Q

What is the nature of dark matter?

A

Insivible - doesn’t reflect any form of electromagnetic radiation.
Composes 95% of the universe’s mass.
Has notiecable gravitational effects.

32
Q

What could dark matter take the form of?

A

Black holes,
Neutrinos
WIMPs

33
Q

What are WIMPs?

A

Weakly Interacting Massive Particles, which are exotic particles.

34
Q

Who was the first to propose the existence of dark matter, and when?

A

Fritz Zwicky in 1933.

35
Q

How was dark matter first proposed to exist?

A

Fritz Zwicky in 1933 noticed the unusual rotation of galaxy arms - several times faster than expected.
He used a gravitational model suggesting that the rotation of stars depends on the mass of the nucleus and distance from the nucleus.

36
Q

Were spiral arms rotating faster or slower than expected?

A

Faster

37
Q

What is the significance of dark matter?

A

Explains the unusual rotation of galaxies.
Explains gravitational lensing, where light bends around huge amounts of matter.
Could suggest that the universe’s expansion will slow at some point due to extra matter.

38
Q

What is gravitational lensing?

A

The observed multiple and distorted images of the same galaxy as light bends around huge amounts of matter.

39
Q

What is dark energy?

A

A theoretical repulsive force acting in opposition to gravity that may be responsible for the acceleration of expansion of the universe.

40
Q

Does dark energy occupy the entire universe?

A

Yes. It is believed to occupy the entire universe and accounts for most of the energy in it.

41
Q

What is the significance of dark energy (in short)?

A

The rate of expansion is not slowing down, and will end with a big crunch.

42
Q

What happed in 1998?

A

Until 20 years ago, there was a general consensus that rate of expasion was slowing down. 2 teams of astronomers used observations of distant supernovae to suggest that the rate of expansion of the universe was accelerating.

43
Q

Who coined the term dark energy?

A

Michael Turner

44
Q

Why will the universe end with a ‘big crunch’?

A

The mass of the universe determines its density.
If the density of the universe exceeds a critical density, the universe’s expansion will halt.
Gravitational forces willn eventually halt expansion and the universe will experience a ‘big crunch’.

45
Q

What evidence is there for an expanding universe?

A

CMB was predicted in 1948 to have a low temperature and a wavelength of microwaves, as the expanding universe would have cooled and stretched radiation.
The composition of elements the early universe has been predicted and in what proportions.
The Doppler Effect has been discovered by Doppler and Hubble through observation.
There have been observations from other astronomers of the most distant galaxies that have confirmed this.

46
Q

How did the universe evolve?

A
  1. In the beginning, the universe was filled homogenously with extremely high energy density and temperature.
  2. The universe was cooling rapidly.
  3. Particle-antiparticle pairs were created and destroyed continuously.
  4. Different particles formed.
  5. Temperatures eventually became too low to support these pairs.
  6. Mass-annihilation took place and left only some protons, neutrons and electrons and no antiparticles.
  7. Neutrons combined with protons to make helium and deuterium nuclei.
  8. Universe cooled further.
  9. Some electrons joined to make atoms, while most were left uncombined as hydrogen nuclei.
  10. Radiation could then decouple from matter and continued through space.
  11. Slightly denser regions began to attract each other.
  12. This formed gas clouds, stars and galaxies.
47
Q

What arguments are there in favour of the Big Bang?

A

CMB - wavelength and temperature
Doppler effect combined with the extrapolation of the universe using general relativity, yielding an infinite density and temperature

48
Q

What arguments are there against the Big Bang?

A

Violates the first law of thermodynamics - cannot create or destroy matter or energy.
Violates the rule that nothing can travel faster than the speed of light.
Philosophical and religious arguments.

49
Q

What does the Steady State model propose?

A

The universe is expanding, but density remains constant because matter is continually being created.

50
Q

What did Einstein advocate?

A

Steady State theory.

51
Q

What does the cyclic universe theory propose?

A

A series of big bangs and big crunches that will continue until the end of time.

52
Q

What are the problems with other therories (alternative to the big bang?)

A

There is a lack of hard evidence to support them.

Astronomy GCSE (7 decks)

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