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Origins of Elements, Evolution of the Universe, Classification of Stars,…

- - - - Mainly created mostly:
        
        Hydrogen
        
        Helium
  - - - AS early as seconds the universe expanded and cooled converting energy to particles
        
        Particles consisted of both matter and anti-matter
        
        Anti-matter
        
        Definition
        
        Matter consisted of elementary particles which are the antiparticles of those making up normal matter
- - - - Everything in the universe was created out of a single point through a big bang, or explosion and it has expanded to the form that we see today
- - - - will be more blue hence, hotter
- - - - Mnemonics
        
        Only
        Boring
        Astronomers
        Find
        Gratitude
        Knowing
        Mnemonics
    - - 28 000 - 50 000
    - - 10 000 - 28 000
    - - 7 500 - 10 000
    - - 6 000 - 7 500
    - - 4 900 - 6 000
    - - 3 500 - 4 900
    - - 2 000 - 3 500
  - - - As they get hotter electrons can make bigger jumps allowing them absorb higher energy photons
- - - - This produces a spread of wavelengths of a spectrum of light
      - Different wavelengths are dispersed by a prism or grating
  - - - density
      - Rotational motion
      - age
      - temperature
- - - - Determined that hot objects like sun behave like blackbodies
- - - - Predicting the relationship between a peak wavelength and a body's temperature
        
        can predict star's temperature
  - - - he suggested that photons behave as discrete packets of energy
        
        quanta
        
        means that
        
        they'll have a certain number of energy associated with them but can only release that energy if certain temperatures are achieved
    - - Said that photons interact with electrons 1-1
- - - - Electrons
        
        those surrounding the nucleus sit within discrete energy levels
        
        absorbs photon's energy
        
        if photon has requirements to excite electron to a higher energy state
        
        energy is proportional to its frequency
        
        Energy released by star originates from its core as black body radiation
        
        transmitted through the star's atmosphere
        
        atmosphere absorbs particular photons
        
        absorbed photons indicates composition of star's atmosphere
      - Spectra
        
        Energy released originates from its core
        
        black body radiation
        
        then transmitted through star's atmosphere
        
        atmosphere absorbs particular photons
        
        absorbed photons indicate the composition of the star's atmosphere
        
        light source is sent through a gas cloud
        
        then represented through a black line on the continuous spectrum
        
        light is absorbed by gas
      - Definition
        
        dark lines along a coloured spectrum which show what colours (or energies) from the incandescent light source have been absorbed by the electrons in the gas
    - - Electrons
        
        those surrounding the nucleus sit within discrete energy levels
        
        excited electrons emit energy in the form of photons
        
        they stay in a higher state called the excited state
        
        when they are far away from the nucleus they are unstable
        
        drop down to orbital state to stabilise by dropping energy
        
        fthe more levels the electron drops the higher the frequency
        
        they also may return to ground state by releasing a photon
        
        equivalent to the energy the previously absorbed
        
        energy of "emitted" photon is proportional to frequency
      - Spectra
        
        due to a photon having an individual frequency and emission spectrum is produced
        
        Frequencies appear as bright lines against a dark background
        
        Frequencies emitted by the light of stars can be analysed against known earth atoms
      - Definition
        
        Coloured lines along a dark background which show the colours that are emitted by electrons when the hot gas loses energy and the electrons decay to their ground states
- - - - Denotes the distance between the sun and the earth
  - - - Distance that light will travel over the space of a year
- - - - Parallax angle is 1 arcsecond
      - Earth's orbital radius is 1 AU
  - - - Useful for describing even larger distances between galaxies
  - - - Distance from Earth to Sun
    - - arcseconds
        
        Covert to degrees by multiplying 1/3600
    - - Distance from Sun to Distant Star
- - - - Is measured in megaparsec
      - Linear relationship between velocity and the distance
  - - - Velocity of recession
        
        Km/s
      - Hubble's constant
        
        co
        
        convert to ms
      - Distance away from us
        
        Mpc
        
        Megaparsec
        
        Convert to Mpc
  - - - Given the distance of how far away we are
- - - - Definition
        
        Expansion may slow and eventually stop in the future
    - - Definition
        
        Universe will stop expanding and start contracting
      - Lead to the big crunch
        
        When everything collapses in on itself
    - - Definition
        
        Universe is expanding at an accelerating rate, so it'll only continue to expand faster
      - Will continue to expand for ever
  - - - Einstein tried to make an equation to have this work
      - Alexander Friedmann
        
        Found mathematical proof that the universe is expanding
      - Definition
        
        The size of the universe is not changing and is static
- - - - He looked at spectra from stars in distant galaxies and comparing it to the sun
        
        Noticed that the pattern of lines were the same but shifted to the red end of spectrum
        
        Red Shift
        
        Interpreted to mean that galaxies were receding away from us at very high velocities
        
        Physical expansion of space was causing this recession
        
        Using the size we can work out how far away they were
- - - - 3 helium nuclei to carbon
    - - Smaller stars stop fusion after helium
        
        leave core filled with
        
        carbon
        
        oxygen
    - - Larger stars continue fusion
        
        leave core filled with iron
- - - - Begin as a cloud of helium dust
        
        held together by gravity
    - - Cloud of hydrogen gas and stellar dust in space held togethr by gravity
    - - Generates heat as pressure increases
        
        Hot enough to ignite hydrogen in middle of star and begin nuclear fusion
    - - depending on how massive it is
        
        the large it is the further up and left it'll be on the HR diagram
  - - - Characterised by the nuclear fusion of hydrogen into helium
      - Nuclear Fusion
        
        How a star generates energy
    - - mass difference converted to energy
        
        using einstein's mass-energy equivalence
        
        Created energy provides a outwards force of pressure which balances the inwards force from gravity
- - - - Core contracts
      - Shell expands
  - - - Dominant fusion process for smaller main sequence stars
        
        This chain reaction fuels most stars
        
        Provides them with enough energy to support their masses for lifetimes
      - Converts 4 hydrogen atoms to 1 helium atom
        
        6 hydrogen nuclei to 1 helium nucleus + 2 spare hydrogen nuclei
      - Energy released expressed as:
    - - Dominant fusion process for larger main sequence stars
        
        Stars which has such crushing weigh that generates higher temperatures
      - 4 hydrogen atoms to 1 helium atom + high energy gamma ray photon
      - Uses a carbon atom to catalyse the reaction
        
        carbon converted back n forth between:
        
        Carbon
        
        Nitrogen
        
        Oxygen
- - - - no nuclear reactions occur in this phase
- - - - stars less massive than our sun release most of their hydrogen and helium
        
        forms planetary nebulae
        
        then settling in as a white dwarf
        
        as cooling continues they migrate to black, cold dwarfs
    - - this results in a supernove
        
        the collapses makes electrons get pushed inside protons causing neutrons
        
        this results in a fight between outward neutron forces trying to move away while gravity tries to bring them closer
        
        If gravity wins
        
        forms a blackhole
        
        If a neutron star forms
        
        It'll form a neutron star
- - - - Main Sequence Star
        This is when they truly undergo fusion and become a true star
        
        Red Giant
        
        Then depending on mass
        
        If Small
        
        White Dwarf
        
        if they are significantly larger in mass
        
        Supernova
        
        Neutron Star
        
        Black Hole
- - - - 8 - 20 solar masses
    - - continues all the way up to iron
        
        helium runs out and explodes
        
        Supernova
        
        Explosion that sends elements from the star's outer layer flying out across the universe
        
        compresses star's core
    - - Small and dense core
      - About 20 km in diameter but much heavier than our sun
  - - - < 8 solar masses
- - - - Infinitely small and dense
      - Gravitational force is so strong it prevents light from escaping
- - - - High luminosity
        
        Colder than main sequence
        
        yet brighter and larger
        
        Stars migrate off main sequence and reach later stages of life
    - - Goes from hot and bright to
        
        Cold and Dim
        
        All stars begin their lives and live out most of their days on the main sequence
        
        fuelled by hydrogen and helium
    - - Very hot but dim and have very long lifetimes yet relatively small
        
        Move to the right of the diagram as they age
        
        Temperature drops
- - - - Temperature (K)
        
        Luminosity relative to Sun
        
        Mass increases as luminosity
        
        Stars get classified as:
        
        main sequence
        
        giants
        
        supergiants
        
        white dwarfs
        
        Stellar Proportions
        
        Main Sequence
        
        90%
        
        White Dwarfs
        
        9%
        
        Giants
      - x-axis is decreasing
      - Axis increments are not constant
- - - - Absorbs all EM radiation
      - Does not reflect any radiation
  - - - dependant on the temperature
  - - - Allows us to:
        
        Estimate temperature if we assume it is a black body
      - Most commonly modelled object as a black body
        
        star
        
        Absorbs all the light that hits the,
        
        Emission of light is dependant on its temperature
- - - - Wavelength
        
        Smaller Wavelength
        
        Higher Frequency
        
        Higher Energy
        
        More Radiation Emitted
      - Spectral Radiance
        
        Measure of how much energy comes out of the blackbody at a specific wavelength
    - - Wavelength at which maximum occurs is unique to a particular temperature
    - - Peak moves further left
      - Wavelengths get shorter
        
        more radiation emitted