GCSE Astronomy: Stellar Evolution

Correct Answer: Nebula

Correct Answer: Black hole

Model Answer: A nebula is where stars are born. A planetary nebula is formed when a small star dies and sheds its outer layers.

Correct Answer: White dwarf.

Marking Scheme (Any 6 points):

1. Gas in nebula disturbed by gravity of nearby phenomena (e.g., black hole, passing solar system, gravitational waves).
2. Clumps of gas form and draw gas inwards.
3. Collapsing lump rotates and forms a disc of gas and dust.
4. Disc rotates faster and draws in more material, forming a hot dense core called a protostar.
5. Friction between fast-moving particles causes the protostar to heat up.
6. When the temperature is high enough, hydrogen atoms fuse to form helium.
7. Bipolar flow erupts and blows away remaining gas and dust.
8. Remaining gas and dust goes on to form planets.

Marking Scheme:

• During the early formation of the solar system, the area closer to the sun was too warm for gases to condense into solids.
• Only heavier materials were able to group together to form planets. Rocky planets are smaller in size due to the rarity of metals in the molecular cloud.
• Further out, the temperature was low enough for some gases to solidify. Due to the abundance of these gases, gas planets initially grew larger than inner planets.
• This allowed them to gain enough mass to capture very light elements (like hydrogen and helium), enabling them to grow to enormous sizes.

Model Answer: The main part of a star's life where it fuses hydrogen into helium.

Model Diagram:

Self-Check Checklist (1 Mark per correct item, up to 5 total):

• Axes properly labelled with correct units.
• Main sequence plotted correctly.
• Giants and Supergiants drawn in the correct place.
• White dwarfs plotted correctly.
• The Sun accurately placed and labelled.

Marking Scheme:

1. Expands to a red giant (stops fusing hydrogen and starts fusing helium).
2. Because the outward radiation pressure from the fusion is greater than the gravitational pressure.
3. The outward force due to fusion and inward force due to gravity become unbalanced.
4. The star stops expanding when radiation pressure becomes equal to the inward force from gravity again.

Model Answer: Yes, because the fusion reaction happens a lot faster due to the higher mass creating higher gravity/core pressures.

Correct Answer: Iron.

Marking Scheme (Any 5 points):

• Fusion pressure disappears, leaving gravity as the only dominant force.
• The star implodes.
• The star surpasses electron degeneracy pressure.
• Electrons and protons are forced together to form neutrons.
• Neutron degeneracy pressure is reached, generating a catastrophic shockwave that causes the star to explode in a supernova.
• A neutron star remains if the parent star was slightly smaller.
• For ultra-massive stars, neutron degeneracy pressure is overcome completely, leaving a black hole behind.

Self-Check Scheme: Ensure your layout shows the step-by-step collision of protons ($^1\text{H}$) merging to eventually create Helium-4 ($^4\text{He}$), releasing positrons, neutrinos, and gamma-ray photons ($\gamma$) along the way.

Marking Scheme (Any 3 points):

1. Outward fusion pressure stops.
2. Inward force of gravity causes the star to collapse/implode rapidly.
3. Neutron degeneracy pressure is suddenly reached.
4. This creates a massive rebound shockwave that blows the outer layers of the star apart.

Marking Scheme:

1. Observing gravitational effects/orbital anomalies on nearby visible objects.
2. Detecting high-energy radiation signatures (like X-rays) emitted from the accretion disc.

Note: Allow 1 mark for "seeing the radiation given off", but penalize language precision if the accretion disk isn't implied.

Model Answer:

• A pulsar is a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation.
• A quasar is an extremely luminous active galactic nucleus (AGN) powered by a supermassive black hole feeding on a massive surrounding gaseous accretion disk.