E6 Galaxies and the expanding universe (HL only)

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E6 Galaxies and the expanding universe (HL only)
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Galactic cluster
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Galactic supercluster
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Galactic motion

• The red-shift in the light from distant galaxies
  shows that they are moving away from us and thus
  the Universe is expanding.

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Doppler calculations

• ?? v
• ? c
• where ?? is the change in wavelength
• ? is the original wavelength
• v is the speed of the galaxy/star
• c is the speed of light (3 x 108 m.s-1)

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Example
?? v ? c

• A hydrogen line has a wavelength of 434 nm. When
  received from a distant galaxy this line has been
  red-shifted to a wavelength of 486 nm. What is
  the recession speed of the galaxy?
• ?? 486 434 52 nm
• ??/ ? 52/434 0.12
• Hence v 0.12c 3.6 x 107 m.s-1

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Hubbles law
The velocity of a galaxys recession is directly
proportional to its distance from the earth V
H0d
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Hubbles Law v H0d

• H0 72 km.s-1Mpc-1
• This value is difficult to measure due to the
  difficulties and uncertainties in measuring the
  distance to distant galaxies.

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Age of the Universe?

• Assuming that the galaxies have moved with an
  approximate constant speed since the big bang,
  the age of the Universe can be estimated from
  time distance/speed
• d/H0d 1/H0
• 1/(72 x 103 m.s-1.Mpc-1)
• 1/(72 x 103 m.s-1) x 106pc
• 1/(72 x 103 m.s-1) x 106 x 3.09 x 1016 m
• 4.29 x 1017 s 13.6 x 109 years

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Formation of atoms

• The early Universe (lt300,000 years) was so hot
  that atoms could not form and only elementary
  particles could exist (n, p and e).
• As the Universe expanded it cooled meaning that
  first atomic nucei could form (after 3 minutes)
  and later electrons could be bound to nuclei to
  form atoms (after 300 000 years)

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Questions
Page 541 Questions 3, 7, 9, 10,