Topic 8 - Space physics

Question 1

how is a protostar formed?

Answer 1

a cloud of dust and gas called a nebula is pulled together under the force of gravity.

Question 2

how is a main sequence star formed?

Answer 2

the temperature of the protostar rises as the star gets denser and more particles collide. when the temperature is high enough hydrogen nuclei undergo nuclear fusion to form helium nuclei and a lot of energy which keeps the core hot. from here it enters a stable period where the outward pressure caused by nuclear fusion balances the inward force of gravity

Question 3

what happens after the stable period of a star?

Answer 3

the hydrogen begins to run out and the star swells into a red giant if its a small star or a red super giant if its bigger.
it becomes red because the surface cools. fusion of helium occurs and heavier elements (up to iron) are created in the core

Question 4

what happens to a red giant as time goes on?

Answer 4

it becomes unstable and ejects its outer layer of dust and gas, leaving behind a white dwarf.
as it cools down it emits less energy, when it doesn’t emit a significant amount it becomes a black dwarf

Question 5

what happens to red super giants as time goes on?

Answer 5

they begin to glow again as they undergo more fusion and expand and contract several times forming heavy elements like iron.
eventually they explode in a supernova, forming elements heavier than iron and ejecting them into the universe to form other stars and planets. stars and their life cycles produce and distribute all naturally occurring elements

Question 6

what happens after the supernova explodes?

Answer 6

it throws out layers of dust and gas into space, leaving a neutron star. if the star is big enough it will become a black hole

Question 7

what is a black hole?

Answer 7

a super dense point in space that not even light can escape from

Question 8

what is a neutron star?

Answer 8

a very dense core left behind from an exploding supernova

Question 9

what is a white dwarf?

Answer 9

a hot dense solid core formed from an unstable red giant

Question 10

what is in our solar system?

Answer 10

planets
dwarf planets
moons
artificial satellites

Question 11

what is the milky way?

Answer 11

a galaxy, that’s a massive collection of billions of stars held together by gravity. our solar system is a tiny part of this

Question 12

what are planets?

Answer 12

large objects that orbit a star. there are 8 in our solar system. their gravity must be strong enough to have pulled in any nearby objects apart from their natural satellites

Question 13

what are dwarf planets?

Answer 13

planet-like objects that orbit stars, but don’t meet all the requirements to be a planet

Question 14

what are moons?

Answer 14

a type of natural satellite that orbit planets

Question 15

what are artificial satellites?

Answer 15

satellites that humans have built that generally orbit earth

Question 16

how do planets orbit around the sun?

Answer 16

they are travelling in almost circular orbits so they are constantly changing direction and therefore changing velocity and constantly accelerating.
it does this because there is a force acting on it that pulls it towards the centre (gravity) but it is already moving so this force causes it to change direction.
it is constantly accelerating toward what its orbiting

Question 17

why do satellites have to move faster, the closer they are to the object they’re orbiting?

Answer 17

the closer to a planet or star, the stronger its gravitational force
the stronger the force, the faster the satellite needs to travel to remain in orbit because its instantaneous velocity needs to stop it from being pulled into the object it is orbiting

Question 18

what happens when the speed of a satellite in stable orbit changes?

Answer 18

the radius of its orbit must also change. faster moving objects will have a stable orbit with a smaller radius than slower ones

Question 19

what evidence do we have that the universe is expanding?

Answer 19

all around us galaxies have an increased wavelength so they’re wavelengths are closer to the red end of the light spectrum this is called red-shift. measurements of red-shift indicate that distant galaxies are receding very quickly further galaxies have more red-shift than near ones so they’re moving away faster

Question 20

what is the theory of how the universe began based on red-shift?

Answer 20

initially all the matter in the universe was in a very small, hot dense space.
then it ‘exploded’ and space started expanding and it hasn’t stopped

Question 21

what do scientists do when they discover new evidence?

Answer 21

they either have to make a new theory or adapt the one they have to explain the new evidence

Question 22

what do scientists think the universe is mostly made up of?

Answer 22

dark matter and dark energy.

Question 23

what is dark matter?

Answer 23

the name given to an unknown substance that holds galaxies together, but doesn’t emit any electromagnetic radiation

Question 24

what is dark energy?

Answer 24

it is thought to be responsible for the accelerated expansion of the universe