Certificate programme in Science: Astronomy Core Module 2 Galaxies

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Certificate programme in Science Astronomy (Core
Module 2)Galaxies Quasars

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

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Course Overview.

• Session 1
• Introduction to the physics of astronomy
• Session 2
• Structure of the Milky Way
• Session 3
• Rotation of the Milky Way
• Session 4
• Evolution of the Milky Way
• Session 5
• Normal Galaxies
• Session 6
• The Cosmic Distance Scale (Frank Flynn)

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Course Overview cont

• Session 7
• Radio Astronomy (Frank Flynn)
• Session 8
• Active Galaxies Quasars (Carolin Crawford)
• Session 9
• Clusters of Galaxies (Carolin Crawford)
• Session 10
• Dark Matter
• Session 11
• The Formation of Galaxies
• Session 12
• Galaxy Formation Cosmology

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Lecture Overview

• Overview of content
• Units, sizes scale
• Observational techniques
• Electromagnetic spectrum
• Absorption
• Emission
• Doppler Shift
• Magnitudes Distance modulus
• Physical measures
• Forces, Potentials
• Newtons laws
• Distance, velocity acceleration
• Circular motion

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Hubble Deep Fields
Ultra Deep Field
Deep Field
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Elliptical Galaxies
M32
M49
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Spiral Galaxies
M31
M74
NGC 4622
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Irregular Galaxies
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Merging Galaxies
Cartwheel
Antennae
M81 M82
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Astronomical Sizes

• Astronomical sizes, masses and distances are
  extremely difficult to imagine.
• ME 6 x 1024 kg
• RE 6,400 km
• How many days would it take to walk around the
  Earth if our walking speed 6 km / hr ?
• How fast is the Earth spinning at its surface (in
  km / s) given that it does one rotation in 24
  hours?

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Important Units

• Parsecs, pc 1 pc 3.086x1016 m
• Astronomical Units, au 1 au 1.496x1011 m
• Speed of Light, c c 3x108 m/s
• Solar Masses, M? M? 2x1030 kg
• Light Years 1 Lt yr 9.47x1015 m
• 1 pc ? Lt yrs
• 1 au ? pc

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2.i Electromagnetic Spectrum
Radio 10km - 30cm
Far-IR 1mm - 6µm
Visible 800nm 390nm
X-rays 1nm 6pm
Microwaves 30cm 1mm
Mid-IR 6µm - 3µm
UV 390nm 1nm
?-rays 6pm gt
Near-IR 3µm 800nm
km 103m
cm 10-2m
µm 10-6m
mm 10-3m
nm 10-9m
pm 10-12m
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Spectra

• White light can be split into its component
  colours or wavelengths
• Spectrum

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Measuring Velocities

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

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Spectra

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

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Example

• ? 3962,
• ?0 3933.7,
• c 3 x 105 km/s

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2.iii Distance Modulus

• Flux can be related to luminosity
• Using this inverse square relation astronomers
  can assign an absolute magnitude to any star.
• Absolute Magnitude apparent magnitude at 10 pc
• Apparent magnitudes between 1 -gt 6

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2.iii Distance Modulus

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2.iii Distance Modulus

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3.i - 3.ii Forces at Work in the Universe

• To understand the Universe in which we live we
  need to understand the balance of forces and
  energy within it.
• Gravity
• Pressure
• Kinetic energy
• Potential energy
• Thermal energy
• All our calculations make use of two very simple
  theories or ideas

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Two Basic Theories

• 1.Newtons three laws of motion
• i) Everything continues in a state of rest unless
  acted upon by an external force
• ii) Force mass x acceleration
• F m a
• iii)For every action (force) there is an equal
  and opposite reaction (force).
• 2. Energy cannot be created or destroyed.

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Equilibrium

• What is meant by equilibrium?
• All the forces in the system are balanced.

MassM
ReactionMg
ForceMg
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Examples
1.
MassM
2.
MassM
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Examples cont
3.
FrictionF1
ReactionR1
Mass M
ForceWMg
ReactionR2
FrictionF2
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Unbalanced Forces

• Now we use the first example but apply a sideways
  force?
• This causes an acceleration because the force is
  unbalanced (Newtons second law)

1.
Accel a F / M
ForceF
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Example Unbalanced
2.
Accel a (F1-F2) / M
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The Force of Gravity

• All objects are attracted to each other by the
  force of gravity.
• The more mass the objects have the stronger the
  force of gravity between them.
• The force of gravity is a weak force and so is
  only noticeable to us if at least one of the
  masses is extremely large, like the Earth.

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Basics of Gravity
Also, the shorter the distance between the two
masses the stronger the force of gravity.
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Basics of Gravity

• Given the following quantities calculate the
  force of gravity between
• The Earth and the Sun
• M? 2 x 1030 kg
• M? 6 x 1024 kg
• R 1.496 x 1011 m
• The Earth and the Moon
• M? 6.4 x 1023 kg
• R 3,844,000 m

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Gravity, Mass Space-time

• We cannot see how gravity interacts with objects
  it is an invisible force.
• However
• We can think of gravity as a distortion of space
  and time.
• This picture helps us to understand how the force
  of gravity actually works.

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Velocity, Distance Acceleration
Car of mass 1000 kg

• Its velocity, v, is given by the equation
• v 2t3, where t is the time travelled in hours
• Plot a graph to calculate
• Its instantaneous acceleration after 4 hours
• the distance travelled after 3 hours
• Its average velocity after 3 hours

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3.iii Velocity, Distance Acceleration

• a ?v / ?t
• a (15-5)/(6-1)
• a 10/5 2 km/hr2
• 2. s v x t
• area under the curve
• ½3(39) 18 km
• ltvgt s / t
• 18 / 3
• 6 km/hr

v2t3
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Velocity, Distance Acceleration

• a ?v / ?t
• a (42-0)/(7-1.8)
• a 42/5.2
• a 8.07 km/hr2
• 2. s v x t
• area under the curve
• 3.33 squares 3.33 x 10 x 1
• 33.3 km
• ltvgt s / t
• ltvgt 33.3/3
• ltvgt 11.1 km/hr

vt23
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3.iv Keplers Laws Orbits

• 1. Planets describe ellipses with the Sun at one
  focus.
• 2. Vector from the Sun to each planet describes
  equal areas in time.

V1gt V2
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Going Round in Circles

• The force of gravity keeps the planets in orbit
  around the Sun.
• People believed that it was necessary to create a
  fictitious centrifugal force because they
  considered an object in circular orbit to be in
  equilibrium. NOT TRUE
• The mass is accelerating because its velocity is
  always changing.

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Going Round in Circles

• What can we work out about the acceleration of
  the object?
• Horizontally
• Velocity does not change therefore there is no
  acceleration
• Vertically
• Therefore, acceleration is radially inwards of
  size

v sin?
v
v cos?
?
v cos?
v
v sin?
r
?
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Keplers Laws Orbits

• Imagine that the orbits are perfectly circular.
• What can we work out from Newtons laws?

3. Orbital periods about the Sun and the axes of
orbits are connected by
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Gravitational Force and Potential

• Potential
• Plot a graph of the potential between the Earth
  and the Sun between 0.05 au and 1 au
• M? 3x10-6 M? G 1.33 x 1020 M?-1m3s-2
• Measure the gradient of the line at r 0.1, 0.5,
  0.75
• Calculate the force between the Earth and the Sun
  at r0.1, 0.5, 0.75 using

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Gravitational Potential Force
Potential (1000 M?ms-2)
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Graphs Gradients
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Graphs Gradients
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Graphs Gradients
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Graphs Gradients
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Graphs Gradients
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Graphs Gradients
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Graphs Gradients