Galaxies, Big Bang

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Galaxies, Big Bang

• Fri., April 27
• Mon., April 30

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Galaxies

• Galaxies contain millions or billions of stars.
• Galaxy - a collection of stars, dust, and gas
  bound together by gravity
• Because stars age at different rates, a galaxy
  may contain many types of stars.

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Galaxies

• Gravity holds galaxies together in clusters.
• Galaxies are not spread evenly throughout space.
• Cluster - a group of stars or galaxies bound by
  gravity
• The Milky Way galaxy and the Andromeda galaxy are
  two of the largest members of the Local Group, a
  cluster of more than 30 galaxies.
• Clusters of galaxies can form even larger groups,
  called superclusters.

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• We live in the Milky Way galaxy.
• Edwin Hubble divided all galaxies into three
  major types spiral, elliptical, and irregular.
• Most of the objects visible in the night sky are
  part of the Milky Way galaxy.
• Scientists use astronomical data to piece
  together a picture of the Milky Way galaxy.

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• The Milky Way is a spiral galaxy.
• Our galaxy is a huge spiraling disk of stars,
  gas, and dust.
• Our solar system is located within a spiral arm.
• The nucleus of the galaxy is dense and has many
  old stars.
• Interstellar matter - the gas and dust located
  between the stars in a galaxy.

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Galaxies

• Elliptical galaxies have no spiral arms.
• Elliptical galaxies are spherical or egg shaped.
• They contain mostly older stars and have little
  interstellar matter.
• Because older stars are red, elliptical galaxies
  often have a reddish color.

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Galaxies

• All other galaxies are irregular galaxies.
• Irregular galaxies lack regular shapes and do not
  have a well-defined structure.
• Some irregular galaxies may be oddly shaped
  because the gravitational influence of nearby
  galaxies distorts their spiral arms.
• galaxies

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Evolution of galaxies

• Quasars may be infant galaxies.
• In 1960, a faint object was matched with a strong
  radio signal. This object was called a quasar.
• quasar quasi-stellar radio sources very luminous
  objects that produce energy at a high rate and
  that are thought to be the most distant objects
  in the universe
• Each quasar has a huge central black hole and a
  large disk of gas and dust around it.

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Evolution of Galaxies

• Galaxies change as they use up their stores of
  gas and dust
• Galaxies also change as a result of collisions.
• As galaxies approach each other, mutual
  gravitational attraction changes their shape.
• Collisions of gas and dust may cause new stars to
  begin forming. horsehead nebula

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The Universe

• Universe - the sum of all space, matter, and
  energy that exist, that have existed in the past,
  and that will exist in the future.
• We see the universe now as it was in the past.
• It takes time for light to travel in space.
• The farther away an object is, the older the
  light that we receive from that object.
• Most of the universe is empty space
• Space is a vacuum with no air and no air
  pressure.

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Expansion of the Universe

• The universe is expanding. expansion
• Observations of spectral lines from other
  galaxies indicated that they were moving away
  from us
• Red shift an apparent shift toward longer
  wavelengths of light caused when a luminous
  object moves away from the observer
• Blue shift an apparent shift toward shorter
  wavelengths of light caused when a luminous
  object moves toward the observer red/blue shiftl

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The Big Bang Theory

• Expansion implies that the universe was once
  smaller.
• Long ago, the entire universe might have been
  contained in an extremely small space.
• All of the matter in the universe appears to
  expand rapidly outward, like a gigantic explosion
• Scientists call this hypothetical explosion the
  big bang. bang

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Big Bang Evidence

• Cosmic background radiation supports the big bang
  theory.
• Cosmic background radiation is a steady but very
  dim signal from all over the sky in the form of
  radiation at microwave wavelengths.
• Many scientists believe that the microwaves are
  dim remnants of the radiation produced during the
  big bang.

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Big Bang Theory

• Radiation dominated the early universe.
• According to the big bang theory, expansion
  cooled the universe enough for matter such as
  protons, neutrons, and electrons to form.
• Processes in stars lead to bigger atoms.
• Once hydrogen atoms formed, stars and galaxies
  began to form, too.
• All elements other than hydrogen and helium form
  in stars.

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Whats Next

• The future of the universe is uncertain.
• The universe is expanding, but the combined
  gravity of all the mass in the universe is also
  pulling the universe inward.
• The competition between these forces leaves three
  possibilities
• 1. The universe will keep expanding forever
• 2. The expansion of the universe will gradually
  slow down, and the universe will approach a limit
  in size.
• 3. The universe will stop expanding and start to
  fall back in on itself

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Whats Next

• The fate of the universe depends on mass.
• If there is not enough mass, the gravitational
  pull will be too small to stop the expansion.
• If there is just the right amount of mass, the
  expansion will continually slow down, but will
  never stop completely.
• If there is too much mass, gravity will
  eventually overcome expansion and the universe
  will contract.

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Technology Advances

• New technology helps scientists test theories.
• Powerful telescopes and other sensitive equipment
  help scientists study the universe.
• Scientists make observations to test theories and
  develop new explanations.

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• Scientists use mathematics to build better
  models.
• Theories can be expressed in mathematical form.
• Mathematical models can be used to help test
  theories that are not easily observed.

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Dark Matter

• There is a debate about dark matter.
• There is more matter in the universe than what is
  visible.
• Scientists call this dark matter.
• Dark matter may be planets, black holes, or brown
  dwarfs (starlike objects that lack enough mass to
  begin fusion.)