Stellar evolution questions

Stellar evolution syllabus

Questions on stellar evolution can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 8.7 understand how stars can be classified according to their colour
• 8.8 know that a star’s colour is related to its surface temperature
• 8.9 describe the evolution of stars of similar mass to the Sun through the following stages: nebula star (main sequence) red giant white dwarf
• 8.10 describe the evolution of stars with a mass larger than the Sun
• 8.11P understand how the brightness of a star at a standard distance can be represented using absolute magnitude
• 8.12P draw the main components of the Hertzsprung–Russell diagram (HR diagram)

How to answer stellar evolution questions

1. Identify the scale and object involved before choosing a gravitational or orbital relationship.
2. Keep the life cycles of Sun-like and high-mass stars separate and in the correct order.
3. Use observations such as red-shift or background radiation as evidence, then state the conclusion.
4. Show conversions for orbital radius, period and speed before calculating.

Stellar evolution example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Star colour and the liquid-water region

November 2024 · Paper 1P · Question 1(d)

Question 1

Diagram 2 shows the region around the Sun, a yellow star, where liquid water can exist on the surface of planets. This is because the surface temperature of the planet is between 0°C and 100°C.

Explain what would happen to the position of the liquid water region if the Sun was replaced with a blue star of the same size.

Final answer

The blue star is hotter than the Sun, so the liquid-water region moves farther away from the star.

Mark scheme points

1. M1 The blue star is hotter than the Sun.
2. M2 The liquid-water region is farther from the star, or has a larger radius.

Explanation

A blue star has a higher surface temperature than the Sun. At the same distance, a planet would receive more heating, so the region where a planet can have a suitable surface temperature lies farther from the star.

Common mistakes

• It is not enough to say that the blue star is hotter: also state that the liquid-water region moves farther away. Saying only that liquid water would become gas does not describe the change in the region’s position.

Example 2: Linking peak wavelength and temperature

June 2022 (R) · Paper 1P · Question 5(c)

Question 2

Table 1 shows the colour of some stars.

Table 1

Star	Colour
Sun	yellow
Rigel	blue
Betelgeuse	red
Arcturus	orange
Sirius	white

The graph shows the relationship between the peak wavelength of light emitted by a star and the surface temperature of the star.

A scientist suggests that the two variables are linked by this formula.

peak wavelength × surface temperature = constant

Use data from the graph to justify this formula.

Final answer

From the graph, at 10 kK the peak wavelength is about 280 nm, so their product is 2800 nm kK. At 20 kK the peak wavelength is about 140 nm, giving the same product, 2800 nm kK. The products agree, so the graph data support the proposed formula.

Mark scheme points

1. M1 Read a pair of values from the graph, for example 10 kK and 280 nm.
2. M2 Multiply the values correctly to find the constant: 280 × 10 = 2800.
3. M3 Use a different pair of graph readings and calculate its product correctly, for example 20 kK and 140 nm: 140 × 20 = 2800.
4. M4 State that the constants agree, so the results support the proposed formula.

Explanation

To test the formula, read two different pairs of values from the graph and multiply the peak wavelength by the surface temperature for each pair. If the products are the same, the data agree with the suggestion that the product is constant.

At 10 kK:  280 nm × 10 kK = 2800 nm kK
At 20 kK:  140 nm × 20 kK = 2800 nm kK

The matching products support the proposed relationship.

Common mistakes

• The examiner report notes that answers without graph data cannot score, while using two pairs and comparing their calculated constants can earn full marks. Include two readings and both products.
• Saying only that wavelength decreases as temperature increases does not test whether their product is constant; show the multiplication and compare the results.

Practise Stellar evolution questions

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.