8.2 Red-Shift

Describe what is meant by red-shift.

• Observed increase in wavelength of light from galaxies

• As galaxies move away from us

• More distant galaxies = moving faster = bigger observed increase in wavelength

What does the observed red-shift provide evidence for?

• Universe is expanding

• Big Bang Theory

What does the Big Bang Theory suggest?

• Universe began from v/ small region

  • extremely hot and dense

What does the fact that distant galaxies are receding faster prove about the universe?

• Provides evidence that space between galaxies is increasing

  • entire universe is expanding

How does red-shift support the Big Bang model?

• Red-shift shows that galaxies are moving apart + universe is expanding outwards

  • extrapolating this backwards suggests that universe must have begun from a v/ small, dense, + extremely hot point

How did Edwin Hubble use observations to support the expanding universe theory?

• Hubble plotted observational data of red-shifted light f/ different galaxies

  • found that velocity of galaxy moving away is directly proportional to its distance — confirming the universe is expanding

What is dark energy?

Hypothesised form of energy — responsible for the universe’s ever increasing rate of expansion

What is dark matter?

Hypothesised type of mass (cannot be observed) — used to explain why some galaxies rotate faster than they should for their observed mass

• The light spectrum from every galaxy includes dark lines.

• The lines have the same pattern.

• The figure shows the position of dark lines in the visible spectra of light from the Sun and from two distant galaxies.

Explain what these light spectra tell us about the velocities of galaxy A and galaxy B. [3 marks]

• Both show red-shift so both are moving away from us

• A shows greater red-shift than B

• So A is travelling faster than B

• The Hubble Space Telescope can detect visible light from distant galaxies.

• The visible light spectra from stars and galaxies include dark lines at specific wavelengths.

• Figure 2 shows the visible light spectra from the Sun and two galaxies.

Explain what conclusions can be made about galaxies A and B. [3 marks]

• Galaxy A has the greater red-shift

• So A is travelling away from us faster than B

• Because A is further away from us than B

• The points on diagram represent galaxies that are moving away from the Milky Way.

• Each arrow represents the velocity of the galaxy relative to the Milky Way.

• Light from all galaxies represented in the diagram is red-shifted.

Explain how above diagram provides evidence for the Big Bang theory. [2 marks]

• The furthest galaxies are moving away from the Milky Way the fastest

• Which suggests that at some time all galaxies started at the same point

• The points on diagram represent galaxies that are moving away from the Milky Way.

• Each arrow represents the velocity of the galaxy relative to the Milky Way.

• Light from all galaxies represented in the diagram is red-shifted.

• Sometimes scientists have to change theories about the universe.

Give the reason why. [1 mark]

There is new evidence that does not fit into the current theory.