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					      Astronomy

Introduction to the universe
     How old is the Universe?
• Age is estimated to be between 12-14
  billion years old with closest figures
  around 13.7 billion.
• Our solar system is about 4.5 billion years
  old.
• The age of the universe is estimated in
  two main ways.
  – Studying globular clusters
  – Observing the most distant objects (quasars)
              Globular Clusters
• Very dense clouds of           • ½ size of sun = 20 billion
  stars of stars.
• All stars in cluster form at   • Sun = 9 billion
  the same time.
• Stars have a life span         • 2 suns = 800 million
  dependent on their size
  (smaller stars burn
  longer)                        • 10 suns = 20 million
• The oldest cluster is
  estimated to be between
  11-18 billion years old.
Distant objects/ expanding universe
• Quasars are very bright distant objects.
• Because light travels at a finite speed,
  they are seen as they existed billions of
  years ago.
• The light from some of the most distant
  quasars is from when the universe was
  only a billion years old.
               The Big Bang
• It is thought that in the beginning, all of the
  matter in the universe was compacted into a
  very dense object only millimeters across.
• After a great explosion all of that matter
  expanded and traveled outward into space.
• Minor differences in densities made some
  objects have more gravity than others and
  attract more matter to themselves eventually
  forming stars/galaxies etc.
   Limitations of the Big Bang
• Based on the shape of the universe which
  is unknown but hypothesized to be flat.
• Does not explain what was (or is now)
  outside the universe.
• Does not state a cause for the Big Bang.
    The present and future of our
             universe
• Today objects are still speeding through space
  from the initial explosion of the big bang.
• It was once thought that the universe would
  oscillate (expand and contract) but recent
  theories suggest that the universe may expand
  forever.
• This is based on information that suggests the
  universe has increased in its acceleration
  outward instead of slowing down.
• It is believed that this is caused by dark energy
  which basically means there is a vacuum outside
  of our universe.
        Objects in the Universe

• The universe is mostly empty space dotted
  with galaxies.
• Galaxies are large systems that contains
  mostly stars. Other objects in a galaxy
  could include gas, dust, asteroids, planets,
  comets, stars at different stages of their
  life cycle etc.
                 Galaxies
• Galaxies come in three main shapes
  – Elliptical
  – Spiral
  – Irregular
  Our galaxy is called the milky way and is a
    spiral galaxy that is approximately 100,000
    light years in diameter.
Elliptical galaxy
Spiral galaxy
Spiral galaxy
Irregular galaxies
      Objects in the Universe
• Inside galaxies you would find things like
  – Stars in different stages of their cycles
  – Gas/dust
  – Planets
  – Asteroids
  – Meteoroids
  – Comets
                  Star cycles
• Many objects in the universe are stars at
  different stages in their “life” cycles.

• Stars go through different stages in their life
  cycles depending on their mass.

• There are three categories of stars in respect to
  mass
   – Low to medium mass
   – High mass
   – Super high mass
 Low-Medium Mass Star Cycles
• A Low-Medium mass
  star is formed in a
  Nebula.
• A nebula is a large
  cloud of dust and gas
Part of a nebula rotates
  and contracts into a
  hot dense clump that
  emits
  energy/light=Star
Low-Medium Mass Star Cycles
• After a low/medium mass star is formed it
  burns anywhere from 100 billion to 10
  billion years. Smaller stars burn longer.
• When a star is burning it’s fuel is
  hydrogen. When a star starts to run out
  of hydrogen it burns up its helium…at this
  stage a low/medium mass star turns into a
  Red Giant.
Low-Medium Mass Star Cycles.
              • At the Red Giant
                stage a low/medium
                mass star cools and
                expands.

              • The outer layers
                starts to drift off into
                space.
Low-Medium Mass Star Cycles
              • After the red giant
                stage, a Low/medium
                mass star’s outer
                layers form a
                Planetary Nebula.
              • The core of the dying
                star is in the middle of
                its drifting outer
                layers.
Low-Medium Mass Star Cycles
              • After most of the
                outer layers have
                drifted away, a
                low/medium mass
                star forms a small
                white dwarf.
              • A white dwarf radiates
                any remaining heat
                until it cools into a
                black dwarf.
Low-Medium Mass Star Cycles
• A the Black Dwarf stage just the small
  core remains.
• This core is mostly carbon and emits no
  energy
Low-Medium Mass Star Cycle
       High Mass Star Cycle
• A high mass star is also “born” in a nebula
  (like all stars) but burns for a shorter
  period of time (a few hundred million)
• After burning its fuel it turns into a Red
  Supergiant.
High Mass Star Cycle
          • The remains of the
            star quickly contract
            and explode in what's
            called a Supernova
High Mass Star Cycle
          • The dense remains of
            the core of the high
            mass star form a
            rapidly spinning
            neutron star or pulsar.

          • Pulsars are small,
            dense and emit
            radiation beams from
            their core.
High mass Star Cycle
Super High Mass Star Cycle
             • A super high mass
               star follows a similar
               cycle to the high
               mass stars but it ends
               its life as a black hole.
             • A black hole is the
               small extremely
               dense remains of a
               super high mass star
               with extremely strong
               gravitational pull.
Super High Mass Star Cycle