19.1+19.2 Objects in the universe, the life cycle of stars

Question 1

what is nebulae?

Answer 1

gigantic clouds of dust and hydrogen gas…. eventually forming stars/ planets

Question 2

what are planets?

Answer 2

spherical bodies that orbit planets

Question 3

what are dwarf planets?

Answer 3

a planet that has not cleared its orbit of other objects

Question 4

what are moons?

Answer 4

spherical bodies that orbit planets

Question 5

what are asteroids?

Answer 5

small, irregular shaped bodies, made of dust and metal, cicrular orbits around stars

remians of planets

Question 6

what are comets?

Answer 6

small, irregular shaped bodies made of dust and ice, eccentric orbits around stars

remains of a solar system

Question 7

what is the solar system?

Answer 7

a system of plannets orbiting a central star

Question 8

what is a galaxy?

Answer 8

a collection of stars and planets

Question 9

what s a universe?

Answer 9

all galaxies in their mass and energy

Question 10

describe the formation of a star

Answer 10

1. nebulae form and come together under gravitational force of attraction
2. denser regions of nebulae pull in more matter, becoming hotter as GPE->KE
3. a protostar forms in the nebula
4. if it becomes massive, dense and hot enough, the GF is able to overcome repulsion between the hydrogen nuclei
5. nuclear fusion of hydrogen nuclei begins and the protostar becomes a main sequencing star

Question 12

draw the life cycle of a star:

Answer 12

Question 13

what is the beginning of all stars lif cycle?

Answer 13

1. denser regions in the nebulae form a protostar
2. when protostar is hot and dense enough, nuclear fusio begins and it becomes a main sequencing star
3. during this phase (GA=RP) so in equillibrium

GA= gravitational attraction, RP= Radial pressure

Question 14

what then happens to low mass stars?

Answer 14

evetually hydrogen nuclei in core run out
1. rate of fusion decreases, star cools, RP decreases
2. GA>RP, so the star collapses
3. GPE->KE so it heats up again
4. fusion of hydrogen nuclei in the shell beings (Red Giant)
5. this then also runs out (whole process x2)
6. white dwarf
7. black dwarf

Question 15

what is electron degneracy pressure?

Answer 15

a pressure exerted by the electrons as the star collapses, since electrons are not allowed to occupy same energy levels.
* this new pressure counters to GFA and so no further collapse of the core is possible

Question 16

what is the chandrasekhar limit?

Answer 16

• limit to mass of core that will be prevented from total collapse of the star due to electron degeneracy pressure
• if mass is more than this this means core will collapse

how much mass the electron pressure can take on

Question 17

which has a shorter life cycle, high mass or low mass stars?

Answer 17

high mass stars becuase they have more mass–>more GPE–> more KE–>faster rate of fusion–> shorter lifetime

Question 18

what is the story of high mass stars?

part 1

Answer 18

1. eventually hydrogen nuclei in the core run out
2. rate of fusion decreases, star cools, RP drops
3. GF>RP, star collapses
4. GPE–> KE, heats up again
5. fusion of helium nuclei in the core beings, star expands
6. fusion of hydrogen in th outer shell begins, outershells expand and cool emitting lower red EM waves (Red super giant)

Question 19

what is the story of a massive star?

part 2

Answer 19

1. the star eventually forms and iron core
2. the iron nuclei cannot be fused together (iron is lowest energy nucleus)
3. star becomes unstable (GAF»RP) becoming a supernova
4. outer shell shed
5. dense core remains: neutron star/ black hole

Question 20

what is a neutron star?

Answer 20

composed of neutrons
small volume
very dense

Question 21

what is a black hole?

Answer 21

GFA is very strong
photons/ lights is unable to escape the gravitational pull

Question 22

what is the difference betwen transitioning from a white dwarf to a black hole or neutron star?

Answer 22

• neutron star: if mass of remiing core> chandrasekhar limit
• black hole: if mass of remaining core is greater than 3 solar masses, GPE collapse creates a very dense body

Question 23

summarise the life cycle of a high mass star

Answer 23

Question 24

summarise the life cycle of a low mass star

Answer 24