Hertzsprung-Russell diagram and stellar life cycleEdexcel International A Level Physics: Mind map

Exam questions on Hertzsprung-Russell diagram and stellar life cycle

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.
   Star Q is cooler than star R, but is much more luminous. Explain how this is possible.2 marks
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.
   Explain why the Sun spends most of its life on the main sequence.2 marks
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.
   Explain why this star has a much shorter main sequence lifetime than the Sun, even though it contains more hydrogen.3 marks