Life cycle of stars

Question 1

What determines the progression of a stars life?

Answer 1

the mass

Question 2

Name all the stages for a low mass star

Answer 2

• stellar nebula
• protostar
• main sequence star
• red giant
• planetary nebula
• white dwarf

Question 3

Name all the stages for a high mass star

Answer 3

• stellar nebula
• protostar
• main sequence star
• red super giant
• supernova

-black hole OR -neutron star

Question 4

stellar nebula

Answer 4

• a cloud of dust and hydrogen gas

- all stars start as part of a nebula

Question 5

protostar

Answer 5

• gravity causes the dust/gas in a nebula to contract, and become denser/condense
• temp increases until hydrogen and other light elements can undergo nuclear fusion
• this produces energy making the core gets brighter and hotter until a protostar is born

Question 6

main sequence star

Answer 6

(takes billions of years, main part of stars life, stable phase)

• nuclear fusion of H atoms increases
• nuclear fusion causes heavier helium nuclei forming and large amounts of energy released
• hotter and brighter, releases energy and radiation from core
• emits light

-equilibrium state - the forces of gravity and gas pushing outwards are balanced

Question 7

red giant

Answer 7

• most of the H gas has been converted to helium
• helium and other light elements fuse to form heavier elements
• the star expands to become a red giant
• releases more energy

-gives off red light

Question 8

planetary nebula

Answer 8

• red giant slowly collapses inwards to form a nebula

- other heavier elements are formed

Question 9

white dwarf

Answer 9

• all nuclear fusion stops due to the elements that cause fusion/the fuel being used up
• loses outer layers

-star collapses to become a white dwarf

• leaves core of the star so hot/dense it grows white
• core/star is smaller than before

-eventually extinguishes

Question 10

red super giant

Answer 10

• fuses together heavier elements
• it has far more fuel so becomes larger, giving off more energy
• gives off red light

Question 11

supernova

Answer 11

• red super giant collapses in on itself in seconds, compressing the core until it reaches a critical point
• causes a massive shockwave
• bright as 10 billion stars, can outshine an entire galaxy for weeks
• releases as much energy in seconds as the star has released up to that point

Question 12

black hole

Answer 12

(formed from larger remnants of a supernova)

• rarely, if a neutron star is big enough the core from a supernova continues to collapse
• it gets smaller until it collapses into an infinitely small point
• the gravitational field strength is so strong that nothing can escape from it, not even light or EM radiation

Question 13

neutron star

Answer 13

• compressed core is left behind
• lots of neutrons and nothing else
• extremely dense
• small amount weighs more than Earth
• small in size
• warmer at first due to work done on it by gravitational collapse, the additional energy raises the temperature

Question 14

What type of star is the Sun?

Answer 14

a low mass star

Question 15

Explain how the fate of a low mass star is different from that of a high mass star [6]

Answer 15

-a low mass star will move off the main sequence and expand to become a red giant before cooling and contracting to become a white dwarf

• a high mass star will move off the main sequence, become a red supergiant and explode in a supernova
• the mass that is left in the core will become a very dense neutron star or a black hole

Question 16

State the stages in the life cycle of

a) low mass stars [4]
b) high mass stars [4]

Answer 16

a) -gravitational attraction of dust and gas in a nebula
- main sequence star/hydrogen fusion
- red giant/expansion after hydrogen burning phase
- white dwarf collapse

b) -gravitational attraction of dust and gas in a nebula
- main sequence star/hydrogen fusion
- red supergiant and supernova explosion
- gravitational collapse to a neutron star for a massive star and to a black hole for a supermassive star

Question 17

Explain why the temperature of white dwarf increases at first despite it losing thermal energy [2]

Answer 17

star radiates thermal energy as it loses heat but gains temperature due to work being done on it by gravitational collapse which raises its temperature

Question 18

Explain the roles of gravity and thermal expansion in the stages of a star’s life cycle [4]

Answer 18

gravity pulls dust and gas together to form a nebula leading eventually to fusion

with thermal pressure balancing this when a main sequence star due to radiation pressure from fusion

until the thermal radiation pressure exceeds the pull of gravity at the end of the star’s main sequence life and it expands

Question 19

How do the first three stages of a low mass star compare to those of a high mass star?

Answer 19

the first stages are shorter in a high mass star than a low mass star