Certificate programme in Science: Astronomy Core Module 4 Cosmology

1
Certificate programme in Science Astronomy (Core
Module 4)Cosmology

• Dr Lisa Jardine-Wright,
• Institute of Astronomy, Cambridge University

2
Lecture Overview

• Jones Lambourne
• Chapters 6.6 8.5
• Measuring The Age of the Universe
• Distance estimators
• Parallax
• Angular size
• Standard Candles
• Velocity Measurements
• Combining Distance Velocity

3
(No Transcript)
4
Measuring Distances

• How do we measure distances?
• Distance ladder
• Parallax

5
Measuring Distances

• How do we measure distances?
• Distance ladder

6
Measuring Distances

• How do we measure distances?
• Distance ladder
• Parallax
• Angular Size

7
(No Transcript)
8
Measuring Distances

• How do we measure distances?
• Distance ladder
• Parallax
• Angular Size
• Standard candles
• Can be thought of as bright beacons which act as
  reference points.

9
Cepheid Variable Stars

• Cepheids are special stars
• because they blink, whats
• more they blink at a rate that
• is precisely related to their
• brightness.
• If we can measure the rate that they are blinking
  then we can infer how bright they are.
• Then we compare how bright they look to us and
  how bright they are as calculated from their
  blink rate.
• Distance

10
Why Do Cepheids Pulse?

• A cepheid is a young star which is burning
  brightly.
• He2 is more opaque and wont let the radiation
  escape, so the radiation heats the gas within the
  star
• Heating increases the pressure of the gas and
  this pressure pushes layers of the star outwards,
  increasing its size and luminosity
• As it expands it cools and becomes transparent
  again.

11
(No Transcript)
12
Measuring the Distance

• First of all we measure the light curve for the
  cepheids in our distant galaxy to calculate the
  period of its pulses.
• The period of our distant Cepheid is then
  compared it to observations of Cepheids in the
  local Universe to calculate its luminosity

13
Brightness -vs- Blink Rate
14
Final Step Distance

• We now know the real luminosity, L of the Cepheid
  and we know the flux, F of light that we measured
  from Earth ? distance.
• Light energy from the Cepheid is emitted in all
  directions.
• Flux is the amount of energy that crosses a
  square metre at a given distance, d.

d
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Practical Cepheid Variables

• Using some real light curves for Cepheid
  Variables we will measure the distances to the 4
  galaxies to which they belong.

20
Measuring Velocities

• How do we measure the velocities of distant
  galaxies?
• Redshift - The astronomical Doppler effect

21
Spectra

• Different chemicals absorb and emit light of
  different colours or wavelengths.

22
Measuring Redshifts Velocities

• The wavelength of the emission and absorption
  lines from elements in our galaxy are redshifted
  due to their velocity away from us.
• If we can measure how much they are redshifted we
  can calculate their velocity
• ? wavelength of line, ?0 wavelength of line
  in the Lab, v velocity of the galaxy and c
  speed of light

23
Example

• ? 3962, ?0 3933.7, c 3 x 105 km/s

24
Practical Hubbles Law

• Using real data
• Estimate distance using angular diameter
• Estimate velocity from redshift.
• Calculate Hubbles constant.

25
Hubbles Law