The evolution of Sun-like Stars

Question 1

What is radiation pressure?

Answer 1

the pressure exerted upon any surface exposed to EM radiation

Question 2

Hydrogen “burning”

Answer 2

The fusion of hydrogen into helium NOT reaction with oxygen

Question 3

Protostar

Answer 3

A young star before it has begun hydrogen fusion

Question 4

Planetary nebulae

Answer 4

A cloud of gas and dust in space

Question 5

Protostar qualities (4)

Answer 5

• Clouds of gas and dust (nebulae) of varying masses that clump together under gravity. (1)
• The irregular clumps rotate and a gravity spins them inwards to form a denser centre – a protostar. (1)
• The protostar is surrounded by a circumstellar disc. (1)
• When the protostar gets hot enough, it begins to fuse elements, producing a strong stellar wind that blows away any surrounding material. (1)

Question 6

Main Sequence (3)

Answer 6

• The inward force of gravity and the outward force due to fusion are in equilibrium – the star is stable.
• Hydrogen nuclei are fused into helium
• The greater the mass of the star, the shorter its main sequence period because it uses its fuel more quickly.

Question 7

Red Giant (2)

Answer 7

• Once the hydrogen runs out, the temperature of the core increases and begins fusing helium nuclei into heavier elements (E.g. Carbon, Oxygen and Beryllium).
• The outer layers of the star expand and cool.

Question 8

Red Giant relating to Stefan’s law

Answer 8

Objects that have a high luminosity and a low surface temperature must have a large surface (Stefan’s Law)

Question 9

Where are red giants found in the HR diagram

Answer 9

Lie on the top right corner

Question 10

White dwarfs relating to Stefan’s law

Answer 10

Objects that have a low luminosity and a high surface temperature must have a low surface area ( Stefan’s Law)

Question 11

Where are white dwarfs found in the HR diagram

Answer 11

Lie on the bottom left hand corner

Question 12

White dwarf (4)

Answer 12

• When a red giant has used up all its fuel, fusion stops and the core contracts as gravity is now greater than the outward force. (1)
• The outer layers are thrown off, forming a planetary nebula around the remaining core. (1)
• The core becomes very dense (1)
• A white dwarf will eventually cool to a black dwarf (1)

Question 13

Shell Hydrogen burning

Answer 13

• When the hydrogen in its core runs out, the outward radiation pressure stops, gravity wins and the core starts to contract
• As the core contracts it heats up. This raises the temperature of hydrogen surrounding the core enough for it to fuse.

Question 14

What stops the core from contracting further

Answer 14

Electron Degeneracy

Question 15

Core Helium burning

Answer 15

The core continues to contract until it is hot and dense enough for helium to fuse into carbon and oxygen.