1. 1
   An astronomy class is studying images of a nebula, a huge cloud of dust and gas (mainly hydrogen and helium) in space, within which regions of higher density are collapsing to form new stars.

   (a)

   An astronomy class observes an image of a nebula, a large cloud of dust and gas in space where new stars are forming. What causes a star to begin forming from this dust and gas?

   [1 mark]

   • ANuclear fission occurring in the cloud
   • BMagnetic repulsion pushing the dust and gas apart
   • CGravitational attraction pulling the dust and gas together
   • DRadiation pressure from a nearby existing star

   (b)

   Once a star has formed and entered its main sequence stage, what is happening inside it?

   [1 mark]

   • AHydrogen nuclei are fusing to form helium, with gravitational and outward forces balanced
   • BThe star is cooling down and gravitational forces have already overcome outward forces
   • CIron nuclei are fusing to form heavier elements
   • DThe star is undergoing nuclear fission of large unstable nuclei

   (c)

   Explain why a star on the main sequence remains a stable size for a very long period of time, rather than collapsing or expanding.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An observatory is comparing two main sequence stars of very different mass, Star X (much more massive) and Star Y (much less massive), to study how a star's mass affects the fusion reactions taking place in its core.

   (a)

   An observatory compares two main sequence stars: Star X has a much greater mass than Star Y. Which star has the hotter core?

   [1 mark]

   • AStar X, the more massive star
   • BStar Y, the less massive star
   • CBoth stars have exactly the same core temperature
   • DNeither star has a core hot enough for fusion

   (b)

   As the more massive star, Star X, evolves, which of these is true about the heavier elements it is able to create by fusion in its core, compared with the less massive Star Y?

   [1 mark]

   • AStar X can fuse nuclei to form heavier elements than Star Y can
   • BStar X can only ever fuse hydrogen into helium, unlike Star Y
   • CBoth stars will always create exactly the same heaviest element
   • DStar Y, being less massive, will create heavier elements than Star X

   (c)

   Explain why the more massive star, Star X, is able to fuse heavier nuclei in its core than the less massive Star Y.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A team of astronomers is modelling the future evolution of two different stars: one similar in mass to the Sun, and one far more massive than the Sun, to predict how each will change over billions of years.

   (a)

   Describe, in the correct order, the stages in the life cycle of a star similar in mass to the Sun, from the main sequence stage onwards.

   [3 marks]

   (b)

   Describe, in the correct order, the stages in the life cycle of a star that is much more massive than the Sun, from the main sequence stage onwards, including how it eventually ends.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science museum exhibit uses the phrase 'we are made of stardust' to explain to visitors that the atoms making up the Earth, and living things, were originally formed inside stars and distributed across the universe.

   (a)

   A science museum exhibit explains that fusion processes in stars are responsible for producing all of the naturally occurring elements found in the universe. Explain how fusion during a star's life cycle, and its eventual death, can account for the existence of elements up to and including those heavier than iron.

   [6 marks]

   (b)

   Evaluate the claim made by the museum exhibit that 'we are made of stardust', explaining how elements formed inside stars come to be present in the Earth and in living things.

   [6 marks]

   Total for question 4: 12 marks

End of questions