Stellar evolution

Question 1

a star’s colour is related to ?

Answer 1

its surface temperature

Question 2

what type of stars are classified by their colour

Answer 2

main sequence stars

Question 3

if a main sequence star is classified as red, then its temperature will be relatively

Answer 3

cool

Question 4

if a main sequence star is classified as blue, then its temperature will be relatively

Answer 4

hot

Question 5

what is a nebula

Answer 5

formed from clouds of dust and gas

Question 6

stars form from

Answer 6

nebulas ( the clouds of gas and dust inside the nebulas)

Question 7

a protostar is formed when

Answer 7

after a gravitational collapse, before a main sequence star

Question 8

how is a protostar formed

Answer 8

the force of gravity inside the nebula pulls particles together until a ball of hot gas forms (this is a protostar)

Question 9

what happens to the star as particles are pulled closer together from gravity

Answer 9

its density increases

Question 10

what happens when density of protostar increases

Answer 10

there will be more frequent collisions between the particles which causes the temperature to increase,

this increase in temperature leads to energy being released and nuclear fusion to happen

Question 11

how does a protostar form and when/how is it classified a mains sequence star (full process)

Answer 11

the force of gravity inside the nebula pulls particles together until a ball of hot gas forms (this is a protostar)

as the particles are pulled closer together, the density of the protostar increases,

meaning more frequent collisions between the particles and temperature is increased which leads to nuclear fusion and energy being released

once nuclear fusion happens in the core, the star os classified as a main sequence star.

Question 12

how long do main sequence stars live for and why

Answer 12

billions of years as they are stable

Question 13

from a main sequence star, if a low mass star is formed, what would it be called

Answer 13

red giant

Question 14

how does a red giant form

Answer 14

after several billions of years the hydrogen causing the fusion runs out.

when it runs out, the fusion also stops

the star will begin to fuse bigger elements like Helium, causing the outer part (surface) of the star to expand

as it expands, it turns into a red giant

Question 15

after a red giant, what star if formed

Answer 15

white dwarf

Question 16

how is a white dwarf formed

Answer 16

Once the helium ( or bigger elements) run out, the star collapses and becomes a white dwarf

• overtime it will cool down and the energy it emits also decreases

Question 17

changes of a white dwarf (temp and colour)

Answer 17

becomes whiter as it contracts and also heats up

Question 18

the smaller the star, the ___ it lives

Answer 18

longer

Question 19

what type of gas are stars made from

Answer 19

hydrogen

Question 20

as a star grows old, what happens to its size

Answer 20

it expands

Question 21

after a main sequence star, a high mass star will finish its sequence in which stages : (3)

Answer 21

• red super giant
• supernova
• neutron star or black hole

Question 22

key differences between a high and low mass star (2)

Answer 22

• higher mass stars remain on the mains sequence for a shorter time before they become a red supergiant
• lower mass stars fuse helium into heavy elements like carbon but high mass stars fuse helium into even heavier elements like iron.

Question 23

for a main sequence star, if it is a high mass star, where does it go next

Answer 23

red supergiant

Question 24

how is a red supergiant formed

Answer 24

• after millions of years, the hydrogen causing the fusion reactions will run out, meaning that the fusion will also stop.
• the star begins to fuse helium which causes the outer part of the star (surface) to expand
• as it expands, its surface cools down and it becomes a red supergiant

Question 25

after a red supergiant, what is formed

Answer 25

a supernova

Question 26

how is a supernova formed

Answer 26

once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly and cause a giant explosion (the explosion is the supernova) - at the centre of the explosion, a dense body called a neutron star will form the outer remnants of the star are ejected into space forming new clouds of dust and gas (nebulas)

Question 27

the heaviest elements are formed during a ?

Answer 27

supernova, and they're ejected into space

Question 28

the nebulae formed from supernovas can form new ?

Answer 28

planetary systems

Question 29

after a supernova, what can be formed (2)

Answer 29

black hole or neutron star

Question 30

what is a black hole

Answer 30

an extremely dense point in space that not even light can escape from

Question 31

how is a black hole formed

Answer 31

because in most massive stars, the neutron star formed at the centre will continue to collapse in on itself under the force of gravity, until it forms a black hole

Question 32

how is a neutron star formed

Answer 32

at the centre of the explosion (supernova), a dense body called a neutron star will form

Question 33

what is the luminosity of a star

Answer 33

the total amount of light energy emitted by the star

Question 34

luminosity is a measure of

Answer 34

the stars brightness or power output

Question 35

apparent magnitude is

Answer 35

the percieved brightness of a star seen from earth

Question 36

apparent magnitude depends on (2)

Answer 36

- luminosity of star - distance star is from earth

Question 37

for apparent magnitude, the brighter the star, the __ the apparent magnitude

Answer 37

lower

Question 38

for apparent magnitude, the dimmer the star, the ___ the apparent magnitude

Answer 38

higher

Question 39

absolute magnitude is

Answer 39

a measure of how bright stars would appear if they were all placed at the same distance from the earth

Question 40

why is it difficult to directly measure the brightness of stars

Answer 40

because a bright star which is far away from the earth might look the same as a dim star that is close to the earth

Question 41

draw the components of a HR diagram