CGP P8 Flashcards
What are stars initally made from
Stars initially form from a cloud of dust and gas called a nebula
How do stars form
. The force of gravity pulls the dust and gas together to form a protostar
. The temperature rises as the star gets denser and more particles collide
. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy, keeping the core of the star hot
Main sequence star
. The star enters a long period where the outward pressure caused by nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards.
. This period is called a main sequence star and typically lasts several billion years
Post-Main sequence star
. Eventually the hydrogen starts to run out and the star swells into a red giant (if it is a small star) or a red super giant. It becomes red and the surface cools, fusion of helium and other elements occurs. Heavier elements are created in the core of the star
White dwarf
. 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
Black dwarf
. As a white dwarf cools down, it emits less energy. When it no longer emits a significant amount, it is called a black dwarf
Big stars
. 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.
. 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 all naturally occurring elements
Black hole
. 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
Solar System
The solar system is all the stuff that orbits our sun. This includes things like:
. Planets - There are 8 in our solar system.
They have to be large enough to have cleared their neighborhoods meaning their gravity is strong enough to have pulled any nearby objects apart from their natural satellites
. Dwarf planets - Planet like objects that orbit stars but don’t meet the rules for being a planet
. Moons - These orbit planets, they’re a type of natural satellite (not man made)
. Artificial satellites - Satellites humans have built, generally orbit the earth
Milky way
. Our solar system is a tiny part of the Milky Way Galaxy
. This is a massive collection of billions of stars that are all held together by gravity
Size of orbit
The size of the orbit depends on the objects speed
. The closer you get to the star or planet, the stronger the gravitational force is
. 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)
. 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
Gravity and an objects orbit
. The planets move around the sun in almost circular orbits
. 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)
. For an object to accelerate there must be a force acting on it. This force is directed to the center of the circle
. This force would cause the object to just fall towards whatever it was orbiting, but as object is already moving, it just causes it to change its direction
. The object keeps accelerating towards what it’s orbiting but the instantaneous velocity keeps it travelling in a circle
. The force that makes this happen is provided by the gravitational force between the planet and the sun
Evidence The Universe is Expanding
. When we look at light from most distant galaxies, we find that the wavelength has increased
. The wavelengths are all longer than they should be - they’re shifted towards the red end of the spectrum. This is called red-shift
. This suggests the source of light is moving away from us. Measurements of the red-shift indicate that these distant galaxies are moving away from us
. More distant galaxies have greater red-shifts than nearer ones. This means that more distant galaxies are moving away faster than nearer ones
. This conclusion appears to be that the whole universe itself is expanding
Balloon example
. Imagine a balloon covered with pompoms, as you blow into the balloon it stretches
. The pompoms move away from each other
. The balloon represents the universe and each pompom is a galaxy. As time goes on, space stretches and expands, moving the galaxies away from each other.
. This is a simple model but it shows how the expansion of space makes it look like galaxies are moving away from us
What is the theory of the Big Bang
. Initially, all the matter in the universe occupied a very small space. This tiny space was very dense and so was very hot
. Then it exploded - space started expanding, and the expansion is still going on
