8. Space Physics Flashcards
How many stars are in our solar system?
One - the sun
What are natural satellites?
The moons that orbit planets
What is our solar system a small part of?
The Milky Way galaxy
Why is Pluto no longer classified as a planet?
- other objects started to orbit near Pluto with masses similar to pluto (Kuipur belt)
- as well as orbiting, a planet has to ‘clear the neighbourhood around it’s orbit’ which pluto has not done
What keeps the planets in their circular orbit around the sun?
- gravity
* don’t fall as they’re moving very quickly - centripetal force
What is a centripetal force?
When an object moves in a circular path and there is a resultant force acting towards the centre of the circle
When does the size of the centripetal force increase?
- when the MASS or SPEED of the object increases (more MOMENTUM = bigger force to change it)
- the radius decreases - a tighter turn needs a bigger force
What are some examples of forces that can provide the centripetal force?
- friction (e.g. a car on a roundabout)
* gravity (e.g. a planet)
What does it mean for an object’s velocity and direction if it is travelling in a circle?
- it’s constantly changing direction so it is constantly accelerating
- this means it’s constantly changing velocity (but not changing speed)
How was the solar system formed?
- 6 billion years ago - old star exploded (supernova) and clouds of gas and dust called nebula formed
- the nebula was pulled together due to gravity and formed planets
- if the planets were big, dense and hot enough then a star would have formed and fusion would’ve occurred
Are all stars the same?
They form in the same way but there is a huge range of masses
How are stars formed?
Gravity pulls together a gas nebula which heats up until fusion starts
What is the life cycle of a star that ends up as a black dwarf?
- nebula
- protostar
- main sequence star
- red giant
- white dwarf
- black dwarf
What is the life cycle of a star that ends up as a neutron star?
- nebula
- protostar
- main sequence star
- red super giant
- supernova
- neutron star
What is the life cycle of a star that ends up as a black hole?
- nebula
- protostar
- main sequence star
- red super giant
- black hole
What size are red giants?
About the same size as the sun
What size are super red giants?
Much bigger than the sun
What is it called when a star first begins to shine?
A protostar
What happens when a protostar has contracted enough so that it is very hot and dense?
Nuclear fusion starts and releases energy to form a main sequence star
What type of star is the sun?
A main sequence star
Why is the main sequence the longest stage in a star’s life?
The gravity inwards is balanced by radiation pressure pushing outwards
Why does a star collapse after hydrogen runs out and fusion stops?
Gravity is greater than radiation pressure so the star collapses
How is a red giant formed?
After a star collapses, the star heats up enough for helium to fuse and it expands (radiation pressure > gravity)
Does fusion occur in red giants?
Yes - it forms lighter elements up to iron
What happens for small stars like the sun after fusion stops?
There is a hot core left behind - a white dwarf
How is a black dwarf formed?
A white dwarf cools
What happens for massive stars when fusion stops?
Gravity collapses the star dramatically and it rebounds as a supernova
What happens after a supernova?
A dense core called a neutron star is left over, or a black hole if it’s so dense that light cannot escape from it
How is helium formed in stars?
When a protostar becomes hot and dense enough for fusion - hydrogen fuses to make helium in a main sequence star
How are light elements including iron formed in stars?
During the red giant stage of a star these elements are formed by nuclear fusion
What is the heaviest element formed in a star?
Iron
How are heavy elements formed in stars?
Because the energy of a supernova is so big it can force nuclei to fuse
What are some of the elements formed in supernovae?
gold, uranium
How do we know that our solar system formed from the remnants of a supernova?
The presence of heavy elements like gold - they can only be formed in a supernova
Why is a main sequence star so stable?
Gravity = radiation pressure, and there is enough hydrogen fuel so density and temperature stay constant
What is the Doppler effect?
The change in frequency of a wave, caused by relative motion between the source of the wave and the observer
Why is the pitch higher when a car is moving towards you?
Wavelength is decreased so frequency is increased
Why is the pitch higher when a car is moving away from you?
Wavelength increases so frequency has decreased
What is red-shift?
Hubble’s idea - the increase in wavelength of the light emitted by a distant galaxy moving away from us
What are 4 of Hubble’s ideas?
- distant galaxies are red-shifted
- the further away the galaxy, the larger the red shift
- distant galaxies must be moving away from us
- very distant galaxies must be moving faster than the closer ones
What happens to red shift when a galaxy is further away?
There is a greater red shift
Which has a longer wavelength, red or blue light?
Red
What is a galaxy?
A collection of billions of stars
What did Hubble use red-shift as evidence for?
That the universe is expanding
What are the two main theories about the creation of the universe?
- big bang theory
* steady state theory
What is the big bang theory?
- the universe began with all space, time and matter in a single point which was hot and dense
- an explosion caused it to expand
- the universe has been expanding ever since
What is the steady state theory?
- the universe has always existed
* galaxies are being pushed apart due to matter entering the universe through ‘white holes’
What is the microwave radiation coming from every direction of space?
Cosmic background radiation - created as gamma radiation after the big bang
Why is cosmic background radiation no longer gamma?
As the universe has expanded the wavelength has stretched to longer wavelengths
How is cosmic background radiation evidence for the big bang theory?
It could have only been created during the big bang
