Astronomy (Extended response)

Question 1

Astronomers collect data and use evidence to try to explain the origins of the Universe. For many years, there were two competing theories: the Steady State theory and the Big Bang theory.

Compare and contrast these theories.

Your answer should refer to the nature of any evidence which suggests that the Big Bang theory is the better theory. [6]

Answer 1

• big bang theory states that the Universe started from a single, infinitely dense point
• in a massive explosion
• released ionising radiation
• 13.8 billion years ago
• has been expanding and cooling ever since
• steady state theory says that the universe has always existed
• is expanding
• new matter is formed continuously as it expands

-evidence for the big bang theory is red-shift of galaxies and the cosmic microwave background radiation

red shift:

• spectral lines in absorption spectra are shifted to the red end of the spectrum due to the stretching of light waves when galaxies move away from us
• as the spectral lines from the majority of galaxies show red shift, this suggests that the Universe is expanding

CMBR:

• low energy radiation remnants from the big bang, at a temperature of -270C, due to the cooling of gamma rays that were emitted at the start of the Universe
• the temp suggests that the Universe is the age it has been predicted to be by the big bang theory
• big bang theory is more accepted
• more evidence
• supported by red shift and CMBR
• CMBR doesn’t support steady state as it supports the idea of the birth of the universe

Question 2

Two stars are both in the main sequence stage of their life. Describe what their possible fates could be and explain why these fates might be very different. [6]

Answer 2

• low mass stars expand to become red giants after the main sequence
• low mass stars that become red giants then become white dwarfs
• high mass stars become red supergiants after they move off the main sequence
• high mass red supergiant stars undergo supernova explosions
• remnant cores of supernovae can become neutron stars (1.4 to 3 solar masses)
• most massive stars become black holes (greater mass than 3 solar masses)

-the fate of stars depends on their mass