Hertzsprung-Russell diagram and stellar life cycleEdexcel International A Level Physics: Subtopic test

1. 1
   Astronomers plot a Hertzsprung-Russell diagram, with luminosity on the vertical axis and surface temperature on the horizontal axis, for stars in one region of the Galaxy. Star P has a high surface temperature but a very low luminosity. Star Q has a low surface temperature but a very high luminosity. Star R lies on the diagonal band containing most of the stars, and has the same luminosity and surface temperature as the Sun.

   (a)

   Which type of star is star P?

   [1 mark]

   • AA main sequence star
   • BA red giant
   • CA white dwarf
   • DA red supergiant

   (b)

   Which type of star is star Q?

   [1 mark]

   • AA red giant or supergiant
   • BA white dwarf
   • CA star on the main sequence that is hotter than the Sun
   • DA star on the main sequence that is cooler than the Sun

   (c)

   Star Q is cooler than star R, but is much more luminous. Explain how this is possible.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The Sun is a main sequence star that releases energy by fusing hydrogen into helium in its core. In about five billion years the hydrogen in the core will be used up.

   (a)

   What happens to the position of the Sun on the Hertzsprung-Russell diagram when the core hydrogen is used up?

   [1 mark]

   • AIt moves down and to the left, towards the white dwarf region
   • BIt moves up and to the left, becoming hotter and more luminous
   • CIt moves down along the main sequence to a lower luminosity
   • DIt moves up and to the right, becoming more luminous with a cooler surface

   (b)

   After the Sun has become a red giant, its outer layers are ejected and the core remains. What is this core?

   [1 mark]

   • AA neutron star
   • BA white dwarf
   • CA black hole
   • DA red supergiant

   (c)

   Explain why the Sun spends most of its life on the main sequence.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A star with a mass about 15 times the mass of the Sun lies at the top left of the main sequence on a Hertzsprung-Russell diagram, and has a luminosity far greater than that of the Sun. Astronomers compare its life cycle with that of the Sun.

   (a)

   Explain why this star has a much shorter main sequence lifetime than the Sun, even though it contains more hydrogen.

   [3 marks]

   (b)

   Describe the stages in the life of this star after it leaves the main sequence, up to its final stage.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A teacher is preparing a lesson in which a Hertzsprung-Russell diagram is used to explain how stars change during their lives.

   (a)

   Describe the main features of a Hertzsprung-Russell diagram and explain how the position of a star on it gives information about the star.

   [6 marks]

   (b)

   Compare the life cycle of a star like the Sun with that of a star of much greater mass, referring to the Hertzsprung-Russell diagram, and conclude what determines the fate of a star.

   [6 marks]

   Total for question 4: 12 marks

End of questions