Cosmology COPY

Question 1

What is the doppler effect?

Answer 1

Effects the electromagnetic waves from stars and glalaxies. For a source moving away from the observer there is an apparent increase in the wavelength

Question 2

What is the doppler effect equation?

Answer 2

∆wavelength / wavelength if source was still = v/c

v = velocity of star

c = speed of light

Question 3

When does the doppler effect equation work

Answer 3

As long as the velocity of the source is a lot less than the velocity of the wave

Question 4

What is the doppler effect equation corrisponding to frequency?

Answer 4

∆f / f = v / c

Question 5

What does the doppler effect say for waves moving towards the observer?

Answer 5

The wavelength would appear to decrease and the frequency to increads

Question 6

What happens to the change in frequency, as effected by the doppler effect, if the observer sends waves put which then bounce off the moving object

Answer 6

The change in the frequency, ∆f, is doubled do:

∆f / f = 2v/c

Question 7

What is red shift? Blue shift?

Answer 7

For a source moving away from the observer the wavelength increases moving the lines towards the red of the spectrum

For a source moving towards the observer there would be a blue shift

Question 8

What is the red shift equal to?

Answer 8

The ratio of ∆wavelength / wavelength

v/c

Question 9

What does ‘at a redshift of …’ mean?

Answer 9

The ratio of ∆wavelength / wavelength is …

Question 10

What are binary stars?

Answer 10

Two stars which circulate around each other so=round each other about a common axis

Question 11

What is the time periof of the motion of two binary stars?

Answer 11

1 on frount, the 2 then 2 again

Question 12

Why do the dips in luminosity for binary stars vary?

Answer 12

The big dip is when the dimmer star blocks light from the brighter star and vise versa

Question 13

When is the maximum intensity seen for a binary star system?

Answer 13

When both starts can be seen

Question 14

How can the mass of a binary star using the Doppler Shift

Answer 14

Question 15

Define exoplanets

Answer 15

Planets that are not in our solar system

Question 16

Why are exoplanets difficult to resolve?

Answer 16

• They don’t give out much light and so the light from the star which they are orbiting drowns out this reflected light
• They are so small that most telescopes do not have a good enough resolving power to distinguish them from the star they are orbiting

Question 17

Explain the ‘wobble’ from a star

Answer 17

• When an exoplanet orbits a star, the exoplanet and the star orbit about their centre of mass
• As the star is more massive than the planet, the centre of the mass will be mich closer to the star
• The star will ‘wobble’ about this centre of mass
• When the star wobbles towards towards an observer, the light will be slightly blue shifted. It will be red shifted when the star moves away.
• If doppler shifts are detected then it suggests the prescence of an exoplanetand the minimum mass can be detected

Question 18

When will the ‘wobble’ for detecting exoplanets only work?

Answer 18

When the movement of the planet is alligned with the line of sight of the observer

Question 19

Explain the detection of exoplanets from the transit method

Answer 19

• When an exoplanet passes in frount of a star there will be a small dip in intensity coming from the star as some light is blocked
• The time it takes for the star to go from max to min brightness can be used to measure the size of the planet

Question 20

What are the problems with the transit method to detect exoplanets?

Answer 20

• It is unlikely that an exoplanet will pass in frount of a star in the line of sight of the observer
• The time that the exoplanet is blocking the star for can be very small fraction of the time period of the planet, meaning ti is hard to spot the drops
• A dip in brightness can be caused by other things and stars can have variable intensities.

Question 21

Draw the light cruves for a big planet passing in frount of a star compared to a small planet

Answer 21

Question 22

What distant galaxies experience red shift?

Answer 22

All distant galaxies in all directions and so are all moving away from us

Question 23

What is Hubble’s Law?

Answer 23

Red shift is proportional to the distance of the galaxy from our own.

The further away a galaxy is, the faster it is moving away.

Question 24

Draw a graph showing Hubble’s Law (numbers on axis not needed)

Answer 24

Question 25

What is the Hubble’s Law equation and what are the units of all the components?

Answer 25

v = H₀D

v = velocity in km/s

H₀ = Hubble’s constant (on formula sheet)

D = distance to galaxy in Mpc

Question 26

What is the equation that links intensity, luminosity/power and distance?

Answer 26

I = L/4πD²

Question 27

What is a standard candle?

Answer 27

An astronomical object with a known luminosity

Question 28

Draw the light curve from a type 1a supernova (only need to know x-axis)

Answer 28

Question 29

What is the greatest magnitude of a type 1a supernova?

Answer 29

-19.6

Question 30

What is the value of the Hubble’s constant?

Answer 30

65 kms/Mpc

Question 31

Derive the formula to find the age of the universe using Hubble’s constant

Answer 31

Question 32

How old is the universe?

Answer 32

15 billion years

Question 33

What is assumed when calculating the age of the universe?

Answer 33

The Hubble’s constant has been constant over the life of the universe

Question 34

What is the big bang model?

Answer 34

The universe started off as an infinitely hot, infinitely dense point and has been expanding ever since

Question 35

What is the fraction of helium formed in the early universe?

Answer 35

25%

Question 36

What is the temperature of the universe?

Answer 36

2.7 K

Question 37

Draw the spectrum of CMBR

Answer 37

Question 38

What is the evidence for the Big Bang Theory? (3)

Answer 38

• Spectra from different galaxies in all directions are red shifted. This suggests that the universe is expanding and so must have been denser in the past
• The observation od CMBR, which is the remnants of EM radiation from the early universe
• The theories of particle physics, when applied to the expanding universe, correctly predict the percentage of helium formed in the early universe

Question 39

Give the key features of a quasar. (3)

Answer 39

• Very large red shift and so very different
• Very powerful radio source
• Supermassive black holes which eject huge amounts of material

Question 40

What are active galactic nuclei?

Answer 40

Supermassive black holes which eject huge amounts of material (quasars)

Question 41

What is the evidense for dark matter? (2)

Answer 41

• The centripetal force caused by the gravitational attraction of stars in the outer part of a galaxy is not large enough to keep the outer stars rotating about the centre of the galaxy at the speed it does
• When light travels through a galaxy it is bent by gravitational lensing, the amount it bends shows that there must be more mass in the galaxy that can be accounted for by the mass of the stars which can be seen

Question 42

What effect does dark energy have?

Answer 42

• In addition to the mass we can see and dark matter, it causes space to be flat
• It effects the rate of expansionof the universe (accelerates it)

Question 43

What is the evidence for dark energy?

Answer 43

The distance of distant galaxies from earth can be calculated from the redshift using Hubble’s Law.

These galaxies look lainted than they should for the distance calculated from the redshift, suggesting they are farther away than expected and that the universe has expanded more than expected.

This suggesting accelerated expansion.