The Hidden Lives of Galaxies NSTA 2001 Jim Lochner and Gail Rohrbach, NASA

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The Universe and Galaxies
Friday, February 20, 2004
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The Universe and Galaxies

• What is the universe?
• Everything physical that exists in space and
  time. Sum of all matter and energy that exists
  now, in past, and future. There is only one
  universe.
• How do we measure distances?
• light years distance light travels in 1 year
• Speed of light 3 x 108 m/s
• 1 ly 9.5 x 1015m how do we get this ?

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Some familiar terms

• Star large ball of gas that emits light
• One example?

• Galaxy collection of millions or billions of
  stars bound together by.?

Gravity!
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Brief History

• Sun is 93 million miles from Earth
• It takes light about 8 minutes to reach Earth
• The 3 closest stars besides the sun are in the
  constellation Alpha Centauri 4.3 light years
  away!
• We see their light 4.3 years afterwards!
• We see the universe now as it
• was in the past.

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Earth to Sun and to Alpha Centauri
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Galaxy stellar region
Stellar Region
Sun (solar system too small to be seen on this
scale)
30 light-years
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What is a Galaxy?
Galaxy
a massive collection of stars, gas, and dust
kept together by gravity
200,000 light-years
Andromeda galaxy, nearest galaxy to Milky Way
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What is a Galaxy?
If our solar system was the size of a cell
in the human body, our galaxy would still measure
over one mile across.
(a human cell is 0.00005 meters across)
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What galaxy do we live in?

• Hint it is also a candy bar!

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Milky Way Galaxy

• Our own galaxy, the Milky Way, is about 105,000
  light-years in diameter.
• How long would it take to go from one end to the
  other if we were to travel at the speed of light?

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Milky Way Galaxy

• Narrow band of light in the sky
• Consists of clouds of gas dust
• Interstellar matter the gas and dust in between
  the stars in a galaxy these are materials for
  new stars

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Features of a Galaxy
Milky Way Galaxy
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Spiral Galaxies

• Disk-shaped
• Have spiral arms that contain gas and dust to
  form new stars
• Have bluish tint
• younger stars are
• bluer in color

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Elliptical Galaxies

• Egg-shaped
• No arms, little gas and dust
• Older than spiral galaxies
• Have reddish tint
• Wide range of sizes
• Dwarf smaller than spiral
• Giant 200,000 ly in diameter

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Irregular Galaxies

• No set shape
• Some have little gas and dust, others are clouds
  of intergalactic matter that have never given
  birth to stars

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Summary of Galaxies
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What kind of galaxy?
spiral
elliptical
irregular
spiral
irregular
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Gravity and clusters

• Gravity holds galaxies together
• Galaxies are not spread out evenly
• Cluster group of galaxies bound by gravity
• Super clusters clusters of galaxies largest
  structures in the universe
• Can be 100 million light years across

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Model your own galaxies!

• In groups of two, complete the Model your Own
  Galaxies activity
• When you are done
• Rinse the beaker and toothpick
• Dry them with a paper towel and put them back

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Homework

• Finish write-up for Model your own Galaxies
  activity
• Read pp. 531-534

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Spirals vs. Ellipticals

• Final type of galaxy depends on initial rate of
  star formation
• - If stars form quickly, then galaxy becomes
  elliptical. Stars form within initial
  distribution of gas,and follow their initial
  orbits.
• - If stars form later, the gas has time to
  collapse into a disk. Most stars from within the
  disk. The galaxy becomes a spiral.

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Formation via Galaxy Mergers

• In clusters, galaxies can pass close to one
  another.
• Galaxies can become distorted, and often merge.
• Mergers often lead to giant elliptical galaxies
  at the heart of large clusters.

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Spirals in Grazing Encounter
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Antennae Galaxies