Topic 8 - Space Physics

Question 1

What does our solar system contain?

Answer 1

Within our solar system there is one star, the Sun, plus the eight planets and the dwarf planets that orbit around the Sun. Natural satellites, the moons that orbit planets, are also part of the solar system.

Question 2

What are the 8 planets in our solar system in order from closes to the sun to least?

Answer 2

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

Question 3

What galaxy is our solar system apart of?

Answer 3

Our solar system is a small part of the Milky Way galaxy.

Question 4

What is a planet?

Answer 4

These are large objects which orbit a star. They have to be large enough to have “cleared their neighbourhood”. This means that their gravity is strong enough to have pulled in any nearby objects apart from their natural satellites.

Question 5

What is a dwarf planet?

Answer 5

E.g, Pluto. These are planet like objects that orbit stars, but are too small to meet all of the rules for being a planet.

Question 6

What is a satellite?

Answer 6

These are objects that orbit a second more massive object.

Question 7

What are 2 examples of satellites - with definition?

Answer 7

• Moons — these orbit planets. They are a type of natural satellite (i.e. they’re not man-made).
• Artificial satellites are satellites that humans have built. There are lots orbiting the Earth and some orbiting the Sun and other planets.

Question 8

How was the Sun formed?

Answer 8

The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction. The sun is a main sequence star, in the middle of its stable period.

Question 9

How, at the start of a star’s life cycle, does the dust and gas drawn together by gravity cause fusion reactions?

Answer 9

• The dust and gas from the nebula, spirals in together, due to the force of gravity, to from a protostar.
• Gravitational attraction causes the density of the protostar to increase, and particles within the protostar to collide with each other more frequently.
• This causes the temperature to rise.
• When the temperature is high enough, hydrogen nuclei begin to undergo nuclear fusion to form helium nuclei.

Question 10

What happens after the fusion reactions begin?

Answer 10

• The fusion reactions give out massive amounts of energy which keeps the core of the star hot.
• At this point a star is born.
• Smaller masses of dust and gas around the star may also be pulled together to make planets orbit the star.

Question 11

How do fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star - reference stable period?

Answer 11

• Once a star has been formed, it immediately enters a long stable period.
• The energy released by the nuclear fusion, fusion energy, provides an outward pressure that tries to expand the star, which balances the force of gravity pulling everything inwards. It is in equilibrium.
• In this stable period it’s called a main sequence star and it lasts several billion years.

Question 12

Where do all naturally occurring elements come from?

Answer 12

Fusion processes in stars produce all of the naturally occurring elements. Elements heavier than iron are produced in a supernova.

Question 13

How do fusion processes lead to the formation of new elements?

Answer 13

Eventually the hydrogen, which is undergoing nuclear fusion, begins to run out. Fusion of helium, and other elements, occurs and the star ceases to be a main sequence star. This produces new elements from the fusion of things like helium, etc.

Question 14

How are the elements distributed throughout the universe?

Answer 14

The explosion of a massive star (supernova) distributes the elements throughout the universe.

Question 15

What determines the life cycle of a star?

Answer 15

A star goes through a life cycle. The life cycle is determined by the size of the star.

Question 16

Describe the life cycle of a star the size of the sun.

Answer 16

• A star the size of the sun will expand into a Red Giant when it starts to run out of hydrogen - becomes red because surface cools.
• Then becomes unstable, and ejects its outer layer of dust and gas as a planetary nebula.
• A hot, dense solid core is left behind - a white dwarf.
• As a white dwarf cools down, it emits less energy.
• When it no longer emits a significant amount of energy, it is called a black dwarf and eventually disappears from sight.

Question 17

Describe the life cycle of a star much more massive than the Sun.

Answer 17

• Stars larger than the sun expand into red super giants when they start to run out of hydrogen.
• Red super giants expand + contract several times, forming elements as heavy as iron in various nuclear reactions.
• Once they run out of elements to fuse - they become unstable.
• They explode in a Supernova, forming elements heavier than iron and ejecting them into the universe to from new planets and stars.
• The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core, called a neutron star.
• Or, if the star is big enough, it will become a black hole instead of a neutron star.

Question 18

What is a black hole?

Answer 18

A super dense point in space that not even light can escape from. (don’t emit light, so can’t actually see them)

Question 19

How do planets and satellites remain in circular orbits?

Answer 19

Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.

Question 20

What happens to an objects speed/velocity in a circular orbit?

Answer 20

• If an object is travelling in a circle, it is constantly changing direction, which means it is constantly accelerating.
• This also means it is constantly changing velocity, but not changing speed.

Question 21

How, for circular orbits, does the force of gravity lead to changing velocity but unchanged speed?

Answer 21

• For an object to accelerate, which it constantly does whilst travelling in a circle, there must be a force acting on it. For circular motion, this force is directed towards the centre of the circle.
• In the solar system, the force that is acting towards the centre of the circle is the gravitational force between a planet and the Sun/its satellites.
• An orbit is a balance between the force providing the acceleration, and the forward motion (instantaneous velocity) of the object.
• The object keeps accelerating towards what it’s orbiting, but the instantaneous velocity (which is at right angles to the acceleration and to the force of gravity) keeps it travelling in a circle.

Question 22

Why, for a stable orbit, must the radius change if the speed changes?

Answer 22

• The size of an orbit depends on the object’s speed.
• The closer you get to a star or planet, the stronger the gravitational force.
• The stronger the force, the faster the orbiting object needs to travel to remain in orbit.
• For an object in a stable orbit, if the speed of the object changes, the size (radius) of its orbit must do so too.
• If the object moves faster, the radius of its orbit must be smaller. If it moves slower, the radius must be larger.

Question 23

What is a red-shift?

Answer 23

There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. As the wavelengths are all longer than the should be - they’re shifted towards the red end of the EM spectrum, this effect is called red-shift.

Question 24

When does red-shift occur?

Answer 24

Red-shift occurs when the source of the light is moving away from the observer. You can think of it as the light wave ‘stretching out’ as the source moves away.

Question 25

How does the observed red-shift provide evidence that space itself (the universe) is expanding and supports the Big Bang theory?

Answer 25

• As the light from most distant galaxies has been red-shifted, this suggests that the galaxies are moving away from us.
• Measurements of the red-shift indicate that most distant galaxies are moving away from us (receding) very quickly - and it’s the same result whatever direction you look in.
• More distant galaxies have a greater red-shift than nearer ones. This means that more distant galaxies are moving away faster than the nearer ones.
• This suggests that all galaxies are moving away from each other.
• The conclusion of these results is that the whole universe (space itself) is expanding => big bang theory.

Question 26

What does the Big Bang Theory say?

Answer 26

• The universe began from a very small region that was extremely hot and dense.
• Then it ‘exploded’ - space started expanding, and the expansion is still going.

Question 27

What do observations of supernovae since 1989 suggest?

Answer 27

Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding ever faster.

Question 28

How are scientists able to use observations to arrive at theories such as the Big Bang theory?

Answer 28

• Its supported by red-shift measurements, and the observations of supernovae since 1989.
• This allows for Big Bang Theory, because after a “bang” occurs all of the matter moves away from the point of origin, as seen in red-shift.
• the Big Bang Theory is a widely accepted theory, but it’s only the best guess we have so far based off the evidence we have.

Question 29

Do we understand everything in the universe now? Give examples.

Answer 29

• No.
• Distant galaxies are moving away from us at a faster rate - indicates that the expansion of the universe is accelerating, but we don’t yet know how and why.
• Scientists think that the universe is mostly made up of dark matter and dark energy.
• Dark matter is the name given to an unknown substance which holds galaxies together, but does not emit any electromagnetic radiation.
• Dark energy is thought to be responsible for the accelerated expansion of the universe.
• But no one knows what these things are, so there are many different theories about them.