P7 3

P7 3

Fusion
1. Step 1
  1. Hydrogen + hydrogen -> deutirium + positron + Gamma ray
2. Step 3
  1. Helium-3 + Helium-3 -> Helium-4 + hydrogen + hydrogen
3. Step 2
  1. Deutirium + hydrogen -> Helium-3 (unstable) + gamma ray
4. Overview
5. This releases a huge amount of energy using einsteins theory
Stars
1. Fusion only happens in the middle of the sun where it is hot enough
2. Outside layer of sun is only a few thousand degrees
3. Outer layer is called the photosphere
4. Main sequence stars only fuse hydrogens to heliums
5. A star will eventually run out of hydrogen fuel
Star Lifecycle
1. Red giant
  1. When MS star runs out of hydrogen fuel fusion in the core will slow
  2. As a result the core will be cooler and there will be less outwards pressure
  3. The outer layers will fall inwards towards the core because of gravity
  4. The surface will be cooler and as a result will be red
  5. As the outer layers are pulled against the core, the core gets hotter
  6. As a result new fusion reactions are possible and the star will start fusing heliums
  7. From fusing heliums the star can fuse heavier elements like nitrogen oxygen and carbon
  8. Our sun will only be able to fuse up to carbon - due to its size
  9. Due to the high pressures from fusing heliums (which releases more energy) it will expand and get huge
2. Larger stars
  1. Larger stars will form red supergiants when they run out of fuel
  2. Because they get so big the core can get hotter and can fuse elements beyond carbon
  3. Iron is the most stable element in the universe - a supergiant cannot fuse iron
  4. No more fusion in red supergiants is possible after iron
3. Supernovae
  1. In a red supergiant the core starts getting filled with iron
  2. Then the star cannot fuse anything anymore
  3. When the fusion stops the outer layer collapses in, it hits the iron core and bounces off and there is a huge explosion
  4. This explosion is a supernova and has the capability to block off a galaxy from view for weeks
  5. In supernovas there is enough energy to make elements heavier than iron
  6. Everything heavier than iron is made by supernovae
  7. Our star has traces of heavier elements so that means it is made from leftovers of other stars
4. Neutron stars
  1. The center core of a star can survive a supernova
  2. If the mass is smaller than 2.5x the size of our sun it will become a neutron star
  3. A neutron star consists nearly entirely of neutrons compressed together in a size of just 30km
5. Black holes
  1. A larger collapsed core will have more gravity
  2. So it has so much gravity it can pull in light
  3. So it is a black hole
6. White dwarfs
  1. A small star will eventually build up a core of oxygen and carbon
  2. After the outer layers are lost the core forms a white dwarf
Comparing stars
1. We don't see different types of stars just stars in different stages of their life
2. 90% of stars fall in the main sequence area
3. The sun is in the middle of the diagram
Gas Laws and Kelvin
1. Gases are made of particles widely spaced apart
2. They move in random directions
3. If a gas is trapped in a container the particles will collide with the walls and exert a small force - this is pressure
4. Pressure is measured in N/m2 or Pascals (Pa)
  1. 1Pa is very small
5. 1 earth atmosphere = 101,225 Pa
6. Laws
  1. Boyles law - pressure is inversely proportional to volume (constant temperature) - Pressure x Volume = constant
  2. Charles Law - volume is directly proportional to temperature (constant pressure) - Volume/temperature = constant
  3. Pressure law - pressure is directly proportional to temperature (constant volume) - pressure / temperature = constant
  4. Temperature for these laws needs to be converted to Kelvin
7. Kelvin
  1. An ideal gas is a gas that will reach -273 C without changing its state
  2. No smaller pressure than 0 and no smaller volume than 0
  3. If you back the LOBF of 2 graphs that show relationship of pressure and temperature and volume and temperature - pressure or volume reaches absolute zero at -273 C
  4. To make the graphs directly proportional they invented a new unit - Kelvin
  5. 0K = -273 C
  6. 1 unit of degrees is equal to one unit of Kelvin
  7. Kelvin = Celcius + 273
  8. Celcius = Kelvin - 273
  9. Our sun is 6000 C or 5727 K
How astronomers work
1. Ground based observatory
  1. On surface of earth
  2. Can only observe frequencies of radiation that are allowed through the atmosphere
  3. Optical telescopes are housed within a dome to protect it from weather
  4. Astronomical factors
    1. Light pollution - all street lights etc - light gets scattered up in the atmosphere making it difficult to see light from the outside of the atmosphere
    2. Scintillation - twinkling of stars - earths atmosphere is not completely uniform - as light goes through dense parts of the atmosphere it diffracts - to avoid this you need an observatory at a high altitude where the atmosphere is thinnest
    3. Atmospheric conditions - clouds, air pollution and high water vapour
2. Finding a suitable location
  1. One with minimal light pollution, high altitude, large percentage of clear nights per year
  2. Examples
    1. Chile
    2. Hawai
    3. Australia
    4. Canary islands
  3. Other factors
    1. Cost
    2. Environmental and social impact
    3. Working conditions (altitude sickness)
3. Space telescopes
  1. Can make distant observations of astronomical objects
  2. No interferance from earths atmosphere
  3. Can see frequencies of radiation that is blocked by the atmosphere
  4. Dont have to put up with rain, water vapour and light pollution
  5. Very expensive to put them in space and very expensive to send a maintenence team
4. International Cooperation
  1. Unpredicable may be conflict between countries
  2. 1 Collaberation between experts from different nations can make breakthroughs
  3. 2. The nations can share the financial cost
  4. 3. Possible to share facilities and information
  5. 4. Cultural exchanges on a scientific and personal level
  6. Eg Hubble was built by NASA and had contributions from ESA and is operated by STSI
5. Astronomers work
  1. Spend a lot of time in offices
    1. Analysing data
    2. Creating computer programs to search through and analyse data
    3. Writing research papers and going to meetings
  2. They usually have to make a proposal to carry out an observation
  3. They have a set time period to use the equipment - as some objects can only be seen at certain times in certain places
  4. Some will accept applications from anyone, some will have criteria
  5. Approved observation
    1. Then get your time at the telescope
    2. Then the data is sent by internet to office or by radio waves if it is in space
6. Controlling telescopes
  1. Large telescopes are controlled by computers
  2. Advantages
    1. Much more precise and accurate
    2. Due to the rotation of the earth, objects appear to move, computers can precisely track them
    3. Dont have to be at the observatory to control it
Other life
1. Estimated 100,000,000,000 other stars in milky way
2. Many of these stars have planets
3. Other planets are called exo-planets
4. Our telescopes are so good we can detect a dip in radiation from from the sun which is a planet in orbit passing by
5. Planets have a small gravity pull on their sun, so the sun wobbles a bit - our telescopes can detect those wobbles
6. When a planet goes past a sun we can see the tiny area where the planets atmosphere lies and we can look at the absorbtion spectra to see if it contains oxygen
7. SETI (Search for Extra Terrestrial life)
  1. They havent found anything, no evidence so far

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