Exam Qs: Cosmology

Question 1

State what is meant by the Doppler effect. (2)

Answer 1

change in (apparent) frequency [or wavelength] (1) 
due to relative motion between source and observer (1)

Question 2

According to NASA nearly 2000 exoplanets had been discovered by 2016, and the search continues. One aim of this search is to find an Earth-like planet orbiting a Sun-like star.

Discuss the difficulties associated with the detection of an Earth-like planet orbiting a Sun-like star.
In your answer you should compare the methods that are used in the search and suggest which may be the most successful. (6)

Answer 2

Transit – dips in brightness as planet crosses in front of star from our point of view.
Alignment must be correct for planets to eclipse, so many possible candidates not observed. Earth-like planet could be observed provided not too far away.

Radial velocity (Doppler) – periodic shift in spectra of star due to star’s movement around common centre of mass with planet. 
Earth-like planet mass much less than mass of Sun-like star so effect slight. Earth-like planet could be detected with highly sensitive spectrometers. 

Direct observation – very unlikely as Earth- like planet to small and too near star and too cool to be detected against the brightness of the Sun-like star. Unlikely to be detected.

Question 3

Sketch the light curve for a typical type 1a supernova.

Label the axes with suitable scales.

Answer 3

Absolute magnitude scale gettingg more negative going up

and

Time scale with 0 along axis, going up to between 10 and 400

Line drawn going up and down, with LHS steeper than steepest part of RHS

Line drawn increasing quickly with peak at absolute magnitude between -18 and -20

Question 4

Measurements of type 1a supernovae in 1999 led to a controversy concerning the behaviour of the Universe.

Describe this controversy and how the measurements led to it. (3)

Answer 4

Measurements of supernovae do not agree with predictions (from Hubble’s Law)

So Universe must be expanding at increasing rate/accelerating

(Controversial as) no known energy source for expansion or reference to dark energy

Question 5

Answer 5

Question 6

Evidence to support the Big Bang theory comes from cosmological microwave background radiation and the relative abundance of hydrogen and helium in the Universe.

Explain what is meant by cosmological microwave background radiation and how its existence supports the Big Bang theory. (3)

Answer 6

it is the radiation coming from all parts of the Universe

when the Universe cooled sufficiently for matter and radiation to ‘decouple’, with the combination of protons and electrons to form neutral atoms

this radiation has been red-shifted into the microwave region as the Universe has expanded

OR

This is (em) radiation from all parts of the Universe,

the spectrum has a peak in the microwave region / corresponds to a temperature of 2.7 K

It can be interpreted as the radiation left over from the Big Bang / the photons having been stretched to longer wavelengths and lower energies.

Question 7

Explain how the relative abundance of hydrogen and helium supports the Big Bang theory.(3)

Answer 7

(The Big Bang theory suggests that a very brief period of) fusion occurred (when the Universe was very young), resulting in the production of helium from fusing hydrogen.

Fusion stopped as the Universe then expanded and cooled resulting in a relative abundance of hydrogen and helium in

the ratio of 3:1/ cooled too rapidly for the creation of larger nuclei,
or suitable relevant observation

Question 8

what does hubbles law state

Answer 8

the rate at which a galaxy recedes is directly proportional to its distance from us