Topic 4 - Space Physics

Question 1

life cycle of stars

Answer 1

protostar -> main sequence ->
red ( super ) giant -> white dwarf
-> black dwarf
-> OR neutron star / black hole

Question 2

how are protostars formed?

Answer 2

• formed from planetary nebula, which is cloud of dust and gas
• gravity makes the dust & gas spiral in together to form a protostar

Question 3

how do we get from protostar to star?

Answer 3

• gravitational attraction causes increase in density
• particles within protostar collide more often
• temperature rises and becomes high enough for H nuclei to undergo fusion
• releases lot of energy, star is born

Question 4

what is main sequence star?

Answer 4

• the energy released by nulcear fusion provides an outward pressure
• that is balanced by the force of gravity pulling inwards
• enters long stable period that lasts for millions of years
• Sun is in its’ main sequence stage

Question 5

what happens after main sequence stage?

Answer 5

• H supply of star runs out
• fusion of helium and other elements
• heavier elements up to Fe created in core
• outward pressure caused by fusion is larger than inward pressure of gravity, no longer stable

Question 6

death of stars about size of sun

Answer 6

• expand into red giant
• becomes unstable and ejects outer layer of dust and gas as planetary nebula
• leaves behind white dwarf
• as it cools down it emits less energy, until it no longer emits significant amount : BLACK DWARF

Question 7

death of stars much larger size of sun ( p1)

Answer 7

• expand into red SUPER giants
• forms elements as heavy as Fe
• runs out of elements to fuse and becomes unstable
• explodes in a supernova

Question 8

death of stars much larger size of sun ( p2)

Answer 8

• intense heat generated by supernova forms element heavier than Fe
• ejects them into universe
• leaves behind dense core, neutron star or black hole
• which is super dense and light cannot escape from it `

Question 9

what is the Sun?

Answer 9

the only star in our Solar System

Question 10

order of planets ( My Very Elegant Mother Just Served Us Nachos )

Answer 10

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Question 11

planets

Answer 11

large objects that orbit a star

Question 12

dwarf planets

Answer 12

planet- like objects that orbit stars but are too small to fit criteria

Question 13

moons

Answer 13

natural satellites that orbit planets

Question 14

artificial satellites

Answer 14

satellites that humans have built that orbit planets

Question 15

what galaxy is our Solar System part of?

Answer 15

it is part of the Milky Way Galaxy, which is a collection of billions of stars

Question 16

orbit

Answer 16

a path on which one object moves around another

Question 17

how do planets move around the sun

Answer 17

• planets move around the Sun in circular orbits
• it is constantly changing direction
• constantly changing velocity but keeping speed same

Question 18

how do planets keep changing velocity?

Answer 18

• for an object to accelerate there must be a force acting on it
• this is directed towards the centre of the circle
• gravity between planet and the Sun

Question 19

how do planets move in a circle around a star

Answer 19

• the object keeps accelerating towards what it’s orbiting due to gravity but..
• instantaneous velocity, which is at 90 to force of gravity keeps it travelling in a circle

Question 20

how does radius of orbit affect speed?

Answer 20

• the smaller the radius, the faster the speed of the object

Question 21

red-shift

Answer 21

• when the observed wavelength of light from a source moving away from us increases

Question 21

why is this?

Answer 21

• the closer you get to the object, the stronger the gravitational force
• the stronger the force, the faster the object needs to move

Question 22

light from distant galaxies

Answer 22

• we observer that the wavelength of light from distant galaxies has red-shifted
• this suggests they are moving away
• light from more distant galaxies is even more red-shifted…

Question 23

what does this prove about the universe

Answer 23

• suggesting that they are moving away from us faster
• all galaxies are moving away from each other
• suggesting the universe is expanding

Question 24

what is the Big Bang theory

Answer 24

• all matter in the universe occupied a very small space
• it was very dense and so very hot
• then it ‘exploded’, space started expanding and still going on

Question 25

recent observation about rate of expansion

Answer 25

• expansion of universe is accelerating