Astrophysics 2

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  • Created by: Sagaana
  • Created on: 03-02-20 13:07
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  • Astrophysics 2
    • Stars 2
      • HR diagram
        • The sun has the absolute magnitude of +5 and temperature of the sun is 5700 (G class)
        • Red giants have a high luminosity and  low temperature so they have a high surface area->gaints
        • White dwarfs have a low luminosity but high temperature so they have a low luminosity      ->dwarfs
      • Stellar Evolution
        • nebula
          • protostar
            • main sequence
              • Red giant
                • White Dwarf
                  • low mass stars turn into white dwarfs
                  • prevented from collapsing by electron degeneracy pressure (electrons that exert enough pressure)
              • Red super giant
                • supernova
                  • black hole
                    • escape velocity greater than the speed of light
                    • gravitational field is strong enough to prevent light from escaping
                    • Quasars
                      • They are active galactic nuclei
                      • supermassive blackholes at the centre of galaxies which are feeding (matter falling into these black holes)
                      • Bright radio sources
                        • show a large optical red shift
                      • produced a continuous spectrum = red shifted blamer line
                        • show a large optical red shift
                      • Most distance measurable objects due to their brightness
                    • schwarzschild radius = the distance at which the escape velocity is the speed of light
                  • Neutron star
                    • composed only of neutrons (protons and neutrons fuse together due to gravity)
                    • has density of nuclear matter
                  • A star whose absolute magnitude increase enormously and rapidly
                  • Happen star runs out of fuel and collapses
                  • Gamma rays produced (similar to the total energy output of a star )
                    • highly collimated >>>>>DEATH
    • Cosmology
      • Doppler effect
        • redshift = increase in wavelength of a wave due to the relative motion between an object and observer
          • only true when v is less than speed of light
          • aka "z" can either be red-shift or blue-shift
          • velocity is away from observer
        • blueshift opposite of redshift
          • velocity towards the observer
        • can be seen in spectral lines
      • Hubbles law
        • recessional velocity is directly proportional to its distance away from us
          • due to the expansion of the universe /stretching out of space
          • goes through origin
        • the age of the universe = 1/H(flip the equation)
          • typical age of the universe = 14 billion years
          • This assumes that H is constant and that the universe is expanding at a constant rate.
            • measurement made of type 1a supernovae do not agree with Hubble's law.
              • the expansion of the universe is accelerating and this is cause by dark energy.
      • Big Bang Theory
        • CMBR
          • EM radiation coming from all parts of the universe
            • the radiation has red shifted into the microwave region as universe expanded
            • Produced when the universe cooled after the big bang for combination of electrons and protons to form atoms
        • There is a lot of hydrogen and helium
          • alot of fusion of H and He occured after the big bang
            • this stopped as the universe expanded and cooled
            • ratio H:HE >>> 3:1
      • Detecting Binary Stars and Exoplanets
        • Binary stars
          • Most binary stars are so far away that they cant be resolved
          • Method 1: Eclipsing binary stars
            • the apparent brightness of the system will decrease when the stars eclipse each other
              • this effect is greatest when the dimmer star blocks light from the bright star
          • Method 2:Doppler Shift
            • each star will periodically shift because the relative velocities of each star will change during the orbital period
            • If there have equal mass the shift of both stars will be the same wavelength.
        • exoplanet
          • They are difficult to detect due to
            • small angle subtended by planet so telescope resolution is not good enough
            • The brightness of the planet obscures the brightness of the planet.
          • Detection method 1: Direct observation
            • difficult to see
          • Detection method 2: Transit method
            • The brightness of a star is measured over a long time period
            • When planet passes in front of a star, some light is absorbed
            • Drawback
              • planet must directly pass between us and the star
              • Transit time is short compared to entire orbit time
              • fluctuation in stars brightness can be cause by other means
              • other methods must be used to confirm the planets existence
          • Detection method 3:Radial Velocity
            • the star is monitored over a long period
            • The star wobbles backwards and forward periodically
              • this the stars velocity relative to the Earths change
            • a small can be detected in the stars spectrum
            • Drawback
              • this requires correct orientation of stars
              • other planets can make the star wobble so difficult to analyse
              • the wobble must me detectable so the planet must be larger orbiting close to the star.

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