Explain — 2 marks
Astronomers have discovered that our Sun is approximately 4.6 billion years old and is currently in the middle of its life cycle. Scientists predict that in about 5 billion years, the Sun will undergo significant changes that will affect all planets in our solar system, including Earth.
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Explain what will happen to the Sun as it reaches the end of its main sequence phase.
[2 marks]
Show mark scheme
- {'mark': 1, 'description': 'The Sun will expand / swell / increase in size'}
- {'mark': 1, 'description': 'The Sun will become a red giant / increase in brightness or luminosity'}
Calculate — 3 marks
A astronomy student is observing the Sun and studying how stars change over their lifetime. The Sun is currently in its main sequence stage and has been burning hydrogen in its core for approximately 4.6 billion years. Scientists predict the Sun will remain in this stable stage for another 5 billion years before expanding into a red giant.
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(a) Calculate the total length of time the Sun will spend in its main sequence stage. Give your answer in standard form.
[1 mark]
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(b) The Sun's core temperature is approximately 1.5 × 10^7 K. When the Sun becomes a red giant, its core temperature will increase to about 1.0 × 10^8 K. Calculate how many times hotter the red giant core will be compared to the current core temperature.
[1 mark]
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(c) The Sun's luminosity (brightness) is approximately 3.8 × 10^26 W. A red giant star has a luminosity of 1.9 × 10^28 W. Calculate how many times brighter the red giant is than the Sun.
[1 mark]
Show mark scheme
- (a) Correct addition of 4.6 billion and 5 billion years
- (a) Answer expressed in standard form or billions
- (b) Correct division of the two temperature values
- (b) Appropriate use of standard form arithmetic
- (c) Correct division of the two luminosity values
- (c) Correct handling of powers of 10 in calculation
Define — 2 marks
Astronomers studying distant stars have observed that many stars exist in binary systems, where two stars orbit around a common centre of mass. As these stars age and evolve, they eventually reach the end of their lives. Understanding the key terms used to describe stellar objects and their properties is essential for interpreting astronomical observations.
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(a) Define what is meant by a 'red giant' star.
[1 mark]
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(b) Define what is meant by the 'main sequence' when referring to a star's life cycle.
[1 mark]
Show mark scheme
- (a) A star that has expanded and cooled (after exhausting hydrogen in its core)
- (a) OR: A late stage in a star's life when it has increased in size and decreased in surface temperature
- (a) Accept: 'A star with a large radius and lower surface temperature than when it was on the main sequence'
- (b) The stage/period in a star's life when it is fusing hydrogen into helium in its core
- (b) OR: The longest stage of a star's life when it is stable and burning hydrogen
- (b) Accept: 'Where a star spends most of its lifetime converting hydrogen to helium'
Evaluate — 3 marks
Astronomers are comparing the life cycles of two stars. Star P has a similar mass to our Sun. Star Q has a mass approximately 20 times greater than our Sun. Both stars are currently in the main sequence stage of their evolution.
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(a) State the final stage in the life cycle of a star with a similar mass to our Sun.
[1 mark]
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(b) Evaluate how the final stages of Star Q's life cycle will differ from those of Star P.
[2 marks]
Show mark scheme
- (a) White dwarf
- (b) Star Q will become a red supergiant (while Star P becomes a red giant)
- (b) Star Q will undergo a supernova explosion
- (b) Star Q will become a neutron star or black hole (not a white dwarf)
- (b) Star Q has a shorter lifespan than Star P
Evaluate — 3 marks
An astronomy student is researching the life cycle of stars. She reads two statements online: Statement A claims that all stars eventually become black holes, and Statement B claims that the Sun will eventually expand into a red giant and then become a white dwarf. The student wants to evaluate which statement is more accurate based on stellar physics.
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(a) Evaluate Statement A. Is it correct that all stars become black holes? Explain your answer.
[1 mark]
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(b) Evaluate Statement B by describing the actual life cycle of the Sun and explaining why the Sun's fate differs from that of the most massive stars.
[2 marks]
Show mark scheme
- (a) Statement A is incorrect; only the most massive stars (much more massive than the Sun) can become black holes / most stars do not have sufficient mass to form black holes
- (b) Statement B is correct: the Sun will become a red giant (when hydrogen fusion ends and helium fusion begins in the core) and then become a white dwarf (after shedding its outer layers)
- (b) The Sun's fate differs because it does not have enough mass to undergo further fusion stages or collapse into a black hole; only very massive stars have sufficient gravitational force to continue fusion and eventually form black holes
GCSE Perfect