8 - space

Question 1

cloud of dust and gas / Nebula

Answer 1

Stars initially form from a cloud of dust and gas called a nebula. The force of gravity pulls the dust and gas together to form a protostar.

Question 2

protostar

Answer 2

As the star gets denser, the temperature rises and more particles collide with each other. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion (p.84) to form helium nuclei. This gives out huge amounts of energy, which keeps the core of the star hot. A star is born.

Question 3

Main sequence star

Answer 3

The star enters a long stable period where the outward pressure
(p.67) caused by the nuclear fusion that tries to expand the star
balances the force of gravity pulling everything inwards. In this
stable period, it’s called a main sequence star and it typically lasts
several billion years. The Sun is in the middle of this stable period.

Question 4

red (super) giant

Answer 4

Eventually the hydrogen begins to run out. The star then swells into a red giant (if it’s a small star) or a red super giant (if it’s a larger star). It becomes red because the surface cools. Fusion of helium (and other elements) occurs. Heavier elements (up to iron) are created in the core of the star.

Question 5

white dwarf

Answer 5

A small-to-medium-sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas. This leaves behind a hot, dense, solid core - a white dwarf.

Question 6

black dwarf

Answer 6

As a white dwarf cools down, it emits less and less energy. When it no longer emits a significant amount, it is called a black dwarf.

Question 7

supernova

Answer 7

Big stars, however, start to glow brightly again as they undergo more fusion and expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they’ll explode in a supernova, forming elements heavier than iron and ejecting them into the universe to form new planets and stars. Stars and their life cycles produce and distribute all naturally occurring elements.

Question 8

neutron star / black hole

Answer 8

The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If the star is massive enough, it will become a black hole - a super dense point in space that not even light can escape from.

Question 9

Planets

Answer 9

these are large objects that orbit a star. There are eight in our solar system.
their gravity is strong enough to have pulled in any nearby objects apart from their satellites.

Question 10

Dwarf planets

Answer 10

These are planet-like objects that orbit stars, but don’t meet all of the rules for being a planet.

Question 11

Moons

Answer 11

these orbit planets.
They’re a type of natural satellite (i.e. they’re not man-made).

Question 12

Artificial satellites

Answer 12

satellites that humans have built. They generally orbit the Earth.

Question 13

orbits

Answer 13

1) The planets move around the Sun in almost circular orbits (the same goes for the Moon orbiting the Earth).
2) If an object is travelling in a circle it is constantly changing direction, which means it is constantly accelerating. (Just like a car going around a roundabout.)
3) This also means it is constantly changing velocity (but NOT changing speed).
4) For an object to accelerate, there must be a force acting on it (p.111). This force is directed towards the centre of the circle.
5) This force would cause the object to just fall towards whatever it was orbiting, but as the object is already moving, it just causes it to change its direction.
6) The object keeps accelerating towards what it’s orbiting but the instantaneous velocity (which is at a right angle to the acceleration) keeps it travelling in a circle.
7) The force that makes this happen is provided by the gravitational force (gravity) between the planet and the Sun (or between the planet and its satellites).

Question 14

orbit speed

Answer 14

1) The closer you get to a star or planet, the stronger the gravitational force is.

2) The stronger the force, the faster the orbiting object needs to travel to remain in orbit (to not crash into the object that it’s orbiting).

3) For an object in a stable orbit, if the speed of the object changes, the size (radius) of its orbit must do so too. Faster moving objects will move in a stable orbit with a smaller radius than slower moving ones.

Question 15

red-shift

Answer 15

red shift is the increase in wavelength of light from galaxies as galaxies move away from us - shifted towards the red end of the spectrum.

Question 16

Big Bang

Answer 16

1) Initially, all the matter in the universe occupied a very hot and dense space.
2) Then it ‘exploded’ - space started expanding, and the expansion is still going on.

Question 17

things unknown about the universe

Answer 17

1) The Big Bang theory is the best guess we have so far. Whenever scientists discover new evidence, they have to either make a new theory or change a current one to explain what they’ve observed.
2) There is still lots we don’t know about the universe. Observations of supernovae from 1998 to the present day appear to show that distant galaxies are moving away from us faster and faster (the speed at which they’re receding is increasing).

Question 18

dark matter and dark energy

Answer 18

Currently scientists think 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 really knows what these things are, so there are lots of different theories about it. These theories get tested over time and are either accepted or rejected.