Universe Review Notes

Electromagnetic Spectrum

• Components of a Wave and Regions of the Electromagnetic Spectrum
  • From longest wavelength to shortest:
    • Radio
    • Micro
    • Infrared (IR)
    • Visible Light
    • Ultraviolet (UV)
    • X-ray
    • Gamma

Wavelength, Frequency, and Energy

• Wavelength: How long the wave is (distance between crests).
• Frequency: How often the wave passes.
• Energy: Amount of power the wave has
• Relationship between wavelength and frequency: Inverse relationship, as one goes up the other goes down

Energy Transfer

• Full transfer of energy from the sun to a PV cell:
  • Nuclear Fusion in Sun -> Light -> PV cell -> Electrical Energy

Telescopes and Space Observation

• Main types of telescopes:
  • Radio telescopes:
    • Detect radio waves.
    • Advantage: Can see through dust.
    • Disadvantage: Low resolution
    • Used for determining temperature, age, and to see hydrogen gas
  • Optical telescopes:
    • Detect visible light.
    • Good for determining age
    • Disadvantage: Must be high above atmosphere.
  • Infrared telescopes:
    • Detect infrared light.
    • Detect heat
    • Used to see baby stars
  • X-Ray telescopes:
    • Detect X-rays.
    • Used to see supernovas

Detectors

• Major disadvantage to detectors operating across the full electromagnetic spectrum:
  • Many require being above the atmosphere.

Spectrum Reach

• Portions of the spectrum that make it to the surface of the earth:
  • Visible light
  • Radio waves

Stellar Composition and Life Cycle

• Elements in a star can be identified by examining its emission or absorption spectrum.

Star Lifecycle

• Elements that fuse together in main sequence stars: H fuses to make He.
• Elements that fuse together in red supergiants: He, C, O, Ne, Mg, Si fuse to make Fe.
• Elements heavier than Iron form in supernovas.

Star Formation

• First step all stars take before becoming a star:
  • Gases or dust collect in a nebula and condense into a protostar.

Large-Massed Protostar

• Large-massed protostar:
  • Forms a Supergiant
  • Supernova
  • Can then result in a neutron star (mass > 1.4 * Sun) or a black hole (mass > 10 * Sun).

Average-Mass Protostar

• Average-mass protostar:
  • Main sequence star
  • Red giant
  • Planetary nebula
  • White dwarf.

Spectral Data and Star Stage

• Star primarily composed of helium: Red giant
• Star with a lot of Argon: Red supergiant

Black Holes

• Black hole definition:
  • Dense core left behind after a supernova. Gravity is so strong that not even light can escape and warps space-time
• Detecting black holes:
  • Observe X-rays given off by debris and objects that it pulls in.

Hertzsprung-Russell Diagram

• Vertical axis: absolute magnitude (brightness)
• Horizontal axis: spectral class (temperature)

Star Types

• Top Left: Brightest hottest stars.
• Top Right: Red Giants.
• Bottom Left: White Dwarfs.
• Bottom Right: Dimmest coolest stars.

Doppler Effect

• Doppler effect: When an object emits waves and is moving, the apparent frequency changes.
• Redshifts: Indicate an object is moving away.
• Blueshifts: Indicate an object is moving toward.

Expanding Universe

• Evidence for the universe's expansion.
  • Most distant objects in all directions show red shift based on Hubble's Law
• Hubble's Law: $v = H<em>0D$ where $v$ is the velocity of recession, $H</em>0$ is Hubble's constant, and $D$ is the distance.

Big Bang Theory

• Big Bang: Model for the formation of the universe.
  • Quarks -> Protons -> Atoms -> Stars -> Planets -> Galaxies
• Occurred approximately 13.7 billion years ago.
• Evidence supporting the Big Bang theory:
  • Cosmic background radiation.
  • Hubble's Law.
  • Redshift. $E=hv$
• Elements heavier than lithium come from stellar evolution (fusion in stars and supernovas).