Explain cloud collapse and protostar heating
Trace hydrogen-containing gas and dust through gravitational collapse into a heating protostar.
Exam scope and assessment notes
Extended only (Supplement) · Physics 0972, 2026–2028. Use supplied distances, periods and stated orbital models. Drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall gravitational attraction.
- Distinguish an energy store from a temperature.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What can gravitational attraction do to a gas cloud?
What you will learn
- Trace hydrogen-containing gas and dust through gravitational collapse into a heating protostar.
- Explain contraction before sustained fusion rather than assuming a star appears fully formed.
Start with interstellar material
Stars begin in interstellar clouds of gas and dust that contain hydrogen. Internal gravitational attraction can draw part of a cloud inward. A dense contracting region becomes a protostar; the cloud is not already a mature, stable star simply because it contains hydrogen.
The contracting material becomes hotter as gravitational potential energy decreases and energy is transferred into particle motion and internal energy. Dust and gas descriptions refer to starting material, not a claim that the eventual star is a cool solid dust ball.
Identify what is changing
A protostar is still forming. A sequence cloud → collapse → hotter protostar records changes in configuration and temperature, not a fixed time scale or a guarantee that every cloud fragment produces a star.
Sustained hydrogen fusion requires sufficiently high central conditions. Formation heating precedes the stable hydrogen-fusing stage. An answer that begins with fusion without describing contraction omits the gravitational mechanism requested for the protostar.
Pause and explain
Which sequence describes formation?
Worked example
Explain why a collapsing cloud can become hotter before a stable star is established.
Show the worked solution
- Internal gravity contracts the cloud.
- Gravitational potential energy decreases.
- Energy contributes to increased internal energy and temperature.
Answer Gravitational contraction heats the forming protostar before the stable fusion stage.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name the starting material and cause of contraction.
Give me a hint
Give both the material description and the internal interaction.
Compare my reasoning
- Identify interstellar gas and dust.
- Include hydrogen in the cloud.
- Name internal gravitational attraction.
Hydrogen-containing interstellar gas and dust; internal gravitational attraction.
Look for these in your work
- Name both materials.
- Identify gravity rather than an external flame.
Explain increasing temperature during protostar contraction.
Give me a hint
Trace an energy change rather than only stating “it gets hot”.
Compare my reasoning
- The material draws inward.
- Its gravitational potential energy decreases.
- Energy transferred into internal motion increases temperature.
Contraction transfers gravitational energy into internal energy, heating the protostar.
Look for these in your work
- Link contraction and energy.
- Do not require established stable fusion.
A supplied model loses 18 energy units of gravitational potential energy; 5 units leave as radiation. Find the internal-energy gain and explain its role.
Give me a hint
Use the supplied closed energy account, not an assumed 100% retention.
Compare my reasoning
- Released energy is 18 units.
- Radiation removes 5 units.
- The remaining 13 units increase internal energy.
13 units of internal-energy gain; this supports heating during contraction.
Look for these in your work
- Keep the model boundary.
- Subtract the stated loss.
Common mistakes
- Cloud hydrogen alone is not a stable star.
- Formation heating can precede sustained fusion.
- Not every cloud fragment becomes a star.
What can you explain now?
Which sequence describes formation?
Compare with the explanation
Hydrogen-containing cloud → collapse → hotter protostar
This retains the starting material and the gravitational heating mechanism.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain contraction before sustained fusion rather than assuming a star appears fully formed.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.