Lesson 55 The Structure of the Universe

Name..

Class..Plymstock School Physics Department

Module G485.5 Modelling the Universe

student booklet

Lesson 52 The Structure of the Universe

Objectives

(a) describe the principal contents of the universe, including stars, galaxies and radiation;

(b) describe the solar system in terms of the Sun, planets, planetary satellites and comets;

Outcomes

Be able to describe the principal contents of the universe, including stars, galaxies and radiation.

Be able to describe the solar system in terms of the Sun, planets, planetary satellites and comets.

Write your own definitions of these Keywords:

Universe

Star

Galaxy

Sun

Planet

Moon

Nebulae

Comet

Red giant

White dwarf

Main sequence star

Super red giant

Neutron star

Black hole

Supernova

Binary star

Quasar

Radiation

The Structure of the Universe Research Project

Create a presentation that describes the principal contents of the universe, including:

stars,

galaxies and

radiation

and describes the solar system in terms of the

Sun,

planets,

planetary satellites and

comets.

ALL (E-D) must define each term above

MOST (C-B) will give examples of each in and out of the Solar System as appropriate

SOME will explain the origin of the above elements and create a neat and logical presentation using keywords correctly.

Lesson 53 notes Stars

Objectives

(c) describe the formation of a star, such as our Sun, from interstellar dust and gas;

(d) describe the Suns probable evolution into a red giant and white dwarf;

(e) describe how a star much more massive than our Sun will evolve into a super red giant and then either a neutron star or black hole;

Outcomes

Be able to describe the formation of a star, such as our Sun, from interstellar dust and gas.

Be able to describe the Suns probable evolution into a red giant and white dwarf.

Be able to describe how a star much more massive than our Sun will evolve into a super red giant and then either a neutron star or black hole.

The Hertzsprung-Russell diagram and the evolution of stars

The Hertzsprung-Russell diagram can be used to show the evolution of stars. Two paths are shown:

(a) Figure 1 for stars of similar mass to the Sun ( 3 solar masses)

Lesson 54 questions Stars

Name

( /14)%

Class..

ALL

1.Describe and explain the stages which take place in the birth of a Main Sequence star.

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[Total 5 marks]

2.When a star ceases to be Main Sequence, it may evolve in several different ways.Explain the circumstances which will lead to the formation of a neutron star.

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[Total 4 marks]

3.(i)A star of mass 7 1030 kg becomes a neutron star of radius 10 km. Calculate the average density of the neutron star, assuming that 50% of the original stars mass has been lost.

density = .. kg m3

[3]

(ii)State how the density of a neutron star compares to that of materials commonly found on Earth.

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[2]

[Total 5 marks]

Lesson 55 notes Astronomical distances

Objectives

(f) define distances measured in astronomical units (AU), parsecs (pc) and light-years (ly);

(g) state the approximate magnitudes in metres, of the parsec and light-year;

(h) state Olbers paradox;

(i) interpret Olbers paradox to explain why it suggests that the model of an infinite, static universe is incorrect (HSW 7);

Outcomes

Be able to define distances measured in astronomical units (AU), parsecs (pc) and light-years (ly);

Be able to state the approximate magnitudes in metres, of the parsec and light-year;

Be able to state Olbers paradox.

Be able to interpret Olbers paradox to explain why it suggests that the model of an infinite, static universe is incorrect.

Be able to convert distances from metres to parsecs to light-years.

Radar

A radio pulse can be sent out and the time taken for the reflected pulse to be received is recorded. If we know the speed of electromagnetic radiation in free space and the time between transmission and reception the radar pulse enables us to find the distance of the object.

Parallax

The difference in direction of a star viewed from the two ends of a line with a length equal to the radius of the Earths orbit is called the PARALLAX of the star.

Stars that are close to the earth have a larger parallax than ones far away. In other words their position in the sky against far away stars when viewed from the Earth changes significantly as the Earth orbits the Sun.

By significantly we mean a fraction of a second of arc. In the example shown Centauri (distance 1.33 parsecs) has a parallax of 0.75 of arc.

Astronomical unit

One Astronomical unit (AU) is defined as the mean distance of the Earth from the Sun (1.5x1011 m)

The light year

This is the distance that light travels in free space in one year = 9.5x1015 m

The Parsec

The radius of Earths orbit = 1.5x1011 m, and therefore the distance is found from:

tan(1) = 1.5x1011/d so d = 3.06 x1016 m

1 parsec is the distance at which an object subtends an angle of one second using the radius of the Earths orbit as the baseline.

Distances between galaxies are usually measured in light years or Mega parsecs (Mpc).

1 Parsec = 3.06x1016 m = 2.04x105 AU = 3.26 light years

1 Mega parsec (Mpc) = 3.26x106 light years = 3.097x1022 m

The parallax of a number of stars is shown in the following table:

Star

Parallax

(" of arc)

Distance (l.y)

Star

Parallax

(" of arc)

Distance (l.y)

A Centauri

0.750

4.3

Vega

0.133

25

Barnard's Star

0.545

6.0

Arcturus

0.097

34

Sirius

0.377

8.6

Aldebaran

0.054

60

Procyon

0.285

11.4

Castor

0.001

570

At distances much greater than this the parallax method becomes impossibly difficult to measure. Remember that 1" of arc is the angle subtended by a human head almost of a kilometer away. Therefore the parallax of Castor is the same as the angle subtended by a human head at a distance of almost 750 km!

Another method for measuring larger distances had to be found.

Cepheid variables

The solution came early in the twentieth century as a result of studies of a variable star (one whose brightness changes with time) in the constellation of Cepheus.

The brightness of the star varied in a particular way (see Figure 3) and in 1912 Miss Henrietta Leavitt of Harvard College observatory discovered an important connection between the period and brightness. This is now known as the period-luminosity relationship. Many other stars were found to vary in a similar way and the group of stars was called Cepheid variables. (There are actually two types of Cepheid variable but we will just consider one type here).

The period-luminosity relation means that if you can measure the period of a Cepheid variable you can find its luminosity. Knowing how bright the star really is and then measuring how bright it appears to be will then give the distance of the star from the Earth. The discovery of Cepheid variables in the Andromeda nebula (M31) enabled its distance from Earth (over two million light years) to be found.

Two ways of presenting the period luminosity law are shown by the graphs in Figure 4.

Olbers Paradox

Lesson 56 Astronomical distances

Name

( /8).%.

Class..

ALL

1.The average orbital radius of Jupiter is approximately 5.2 AU.Calculate the orbital radius of Jupiter in metres.

radius = ...................... m

[Total 1 mark]

MOST

2.(a)Suggest why many stars within our galaxy do not conform with Hubbles law.

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[2]

(b)Estimate the age of the Universe, giving your answer in seconds. Show your working and take the Hubble constant to be 75 km s1 Mpc1.

age = .............................. s

[3]

[Total 5 marks]

ALL

3.Large distances in the Universe may be measured in parsecs. Explain what is meant by a parsec.

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[Total 2 marks]

Lesson 57 - The Red Shift

Objectives

(j) select and use the equation

= v

c

(k) describe and interpret Hubbles redshift observations;

(l) state and interpret Hubbles law (HSW 1 & 2);

(m) convert the Hubble constant H0 from its conventional units (km s-1 Mpc-1) to SI (s1);

Outcomes

Be able to select and use the equation

= v

c

Be able to describe Hubbles redshift observations;

Be able to state Hubbles law (HSW 1 & 2);

Be able to describe and interpret Hubbles redshift observations;

Be able to state and interpret Hubbles law (HSW 1 & 2);

Be able to convert the Hubble constant H0 from its conventional units (km s-1 Mpc-1) to SI (s-1);

The Doppler Effect predicts that radiation from sources that are towards us will be shifted towards shorter wavelengths (the blue end of the spectrum in the case of visible light) and towards longer wavelengths (the red end of the spectrum) if they are moving away from us.

Observations of the spectra of galaxies show that the light coming from many of these is shifted significantly towards the red and this shows that they are moving away from us at high speeds, many tens of thousands of kilometres per second. This shift towards the red is called the Red Shift and is very good evidence for the expansion of the Universe and for the origin of the Universe in the Big Bang.

If the Doppler shift of lines within their spectra can be measured their speed of recession can be calculated. The speed (v) relative to the observer on the Earth is given by:

Velocity of galaxy (v) = c/ where is the wavelength of a line in the spectrum on Earth, is the shift in wavelength and c is the speed of light.

A diagrammatic version of the shift of two absorption lines for three galaxies together with their speeds of recession is shown in the following diagram. The comparison spectrum of an element on Earth, at rest compared with the observer, is shown above and below each galactic spectrum.

For very high speeds the simple formula cannot be used and the effects of special relativity have to be allowed for.

It is important to realise that the Doppler shift will depend on the original wavelength and so lines in the red end of the spectrum will be shifted more than those towards the violet end.

Hubbles Law

Hubble measured red shift and distances and plotted these on a graph:-

Olbers paradox was solved by Hubbles discovery because an expanding universe means that the amount of light from a receding galaxy reaching the Earth per second is reduced and also the fact that it is red shifted means that it has less energy when it reaches us! Therefore, the more distant a galaxy, the less of a contribution it makes to the total amount of light here on Earth and hence it is dark at night because the Universe is expanding!

Converting Units

You can convert the value of H to SI units as follows:

Take the Hubble constant H to be 70 kms-1 Mpc-1

and one light year to be 9.46x1015 m

One Parsec = 3.26 light years = 3.0857x1016 m

therefore 1 Mpc = 3.0857x1022 m

So 70 kms-1Mpc-1 = 70x103/ 3.09x1016x106 = 2.27 x 10-18 ms-1m-1

Lesson 58 questions Redshift

Name.

( /31).%..

Class

ALL

1.The mean density of the Universe, 0, is thought to be approximately 1 1026 kg m3.Calculate a value for the Hubble constant H0.

H0 =......................................................... s1

[Total 2 marks]

2.State Hubbles law and define any symbols used.

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[Total 2 marks]

3.Describe Olbers paradox and explain how the work of Edwin Hubble provides an answer.

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[Total 5 marks]

4.In 1929 Edwin Hubble showed that the Universe was expanding by studying the light from stars and galaxies. Explain how.

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[Total 5 marks]

5.(a)Suggest why many stars within our galaxy do not conform with Hubbles law.

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[2]

(b)Estimate the age of the Universe, giving your answer in seconds. Show your working and take the Hubble constant to be 75 km s1 Mpc1.

age = .............................. s

[3]

[Total 5 marks]

MOST

6.Astronomers are searching for planets which orbit distant stars. The planets are not visible from the Earth. Their existence is revealed by the stars motion which causes a shift in the wavelength of the light it emits.A large planet P is shown orbiting a star S in the Fig. 1. Both the star and the planet rotate about their common centre of mass C.

C

S

P

light to Earth

Fig. 1

When measured from a stationary source in the laboratory, a spectral line has a wavelength of 656.3 nm.The light from star S is examined over a period of 74 hours. The change in wavelength for the same spectral line is recorded. The velocity has been calculated and the data shown in Fig. 2.

time / h

/1015 m

velocity / m s1

1

6.7

3.1

6

38.1

17.5

12

66.0

30.3

19

76.0

34.9

23

69.1

31.7

29

43.8

20.1

35

6.8

3.1

41

32.2

14.8

48

66.0

30.3

55

76.0

34.9

61

62.5

28.7

67

32.2

14.8

74

6.1

Fig. 2

(i)Use the Doppler equation relating with velocity v to calculate the change in wavelength for the final velocity of 6.1 m s1.

change in wavelength = .........m

[3]

(ii)Plot a graph of the stars velocity against time using the grid in Fig. 3. The first seven points are already completed. The data required from Fig. 2 are repeated beneath the grid.

0

10

20

30

40

10

20

30

40

10

20

30

40

50

60

70

80

time

velocity / m s

1

/ h

Fig. 3

[2]

time / h

velocity / m s1

41

14.8

48

30.3

55

34.9

61

28.7

67

14.8

74

6.1

(iii)Draw a curve through all the points on the graph.

[1]

(iv)On Fig. 1, mark a point on the stars orbit that would correspond to a velocity of zero on the graph. Label this point X.

[1]

(v)Use your graph to estimate the time T for the planet to make one complete revolution around the star.

time .........................h

[1]

(vi)The mass M of the star is estimated to be 4 1030 kg. Calculate the radius of the planets orbit using the relationship below.

r =

3

2

2

4

GMT

radius = .....................m

[2]

[Total 10 marks]

7.The mean density of the Universe, 0, is thought to be approximately 1 1026 kg m3.Calculate a value for the Hubble constant H0.

H0 = ...........................s1

[Total 2 marks]

Lesson 59 notes The Expanding Universe

Objectives

(n) state the cosmological principle;

(o) describe and explain the significance of the 3K microwave background radiation (HSW 1).

(a) explain that the standard (hot big bang) model of the universe implies a finite age for the universe (HSW 1, 2, 7);(b) select and use the expression age of universe 1/H0;

Outcomes

Be able to state the cosmological principle;

Be able to describe the significance of the 3K microwave background radiation (HSW 1).

Be able to select and use the expression age of universe 1/H0;

Be able to explain the significance of the 3K microwave background radiation (HSW 1).

Be able to explain that the standard (hot big bang) model of the universe implies a finite age for the universe (HSW 1, 2, 7);

The cosmological principle

The cosmological principle says that if you looked at the universe in any direction it would look the same over very large distances. Our view of the Universe is the same as anybody (anything!) elses as the density over large distances is constant. i.e. the Universe is isotropic (the same in all directions) and homogeneous (uniform density).

Cosmic microwave background - the Echo of the Big Bang

The Universe is thought to have begun some 13.7 thousand million years ago with an enormous explosion that we call the Big Bang. The temperatures at that time were unimaginably huge but as time passed since the Big Bang the Universe cooled. The temperature in deep space dropped and dropped. The background radiation moved into the infrared and the cooling continued.

The photons produced in the Big Bang have continued cooling ever since. The temperature of deep space has now reached 2.725K and the temperature will carry on falling as long as the universe continues expanding.

In 1948 George Gamow, Ralph Alpher, and Robert Herman predicted that the remains of this radiation should still be observable even after such an enormous time.

In 1965 two American astronomers, Arno Penzias and Robert Wilson were using the antenna at the Bell laboratories in New Jersey (see photo credit Bell Laboratories) for scanning the sky when they found that there was a background "noise" (like static in a radio). This uniform signal was in the microwave range with a wavelength of about 7 cm and seemed to come from all parts of the sky. Penzias and Wilson tried to get rid of this annoying background interference. They ejected the pigeons living in the horn of the antenna and even cleaned out their droppings but still the signal persisted. (Modern estimates for the peak intensity of this radiation give a wavelength around 2mm).

By pointing the telescope in a variety of directions they concluded that the interference wasn't radiation from our galaxy or extraterrestrial radio sources and because it remained constant throughout the year it couldn't have come from the solar system or even from a 1962 above-ground nuclear test, because in a year that fallout would have shown a decrease.

Finally they realised that it was not random noise causing the signal but something that pervaded the whole Universe. This was the cosmic background radiation with a temperature of around 2.7K and was given an evocative name the echo of the Big Bang. It is the residual radiation predicted by Gamov and others and is the result of the Universe cooling from the unimaginably hot state over the intervening 13000 million years. The detection of the CMB supports the Big Bang idea of the Universe because the cooling of the Universe after the Big Bang would suggest an expansion over many millions of years.

We can detect the radiation produced by this temperature in our homes. It has been estimated that about 1% of the background hiss on your television set is due to the after effects of this enormous fireball.

Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery.

The age of the universe

Since v = H0d

v/d = H0

v=d/t

d/td = H0d

1/t = H0

t = 1/H0

This t is the time it has taken for the galaxies to expand into the space they occupy now. And since all galaxies seem to be accelerating away from every other galaxy it follows that if we rewind back to the beginning they would have all started at the same point.

The best value for the age of the universe is 13+/- 1 billion years. The error comes from our ability to measure the velocity and position of distant galaxies from their luminosity and Redshift.

Lesson 59 questions - The Expanding Universe

Name

( /24)..%.

Class.

ALL

1.State the Cosmological Principle.

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[Total 2 marks]

2.Describe the important properties of the cosmic microwave background radiation and how the standard model of the Universe explains these properties. Explain their significance as evidence for the past evolution of the Universe.

In your answer, you should make clear how your explanation links with the evidence.

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[Total 5 marks]

3.State Hubbles law and define any symbols used.

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[Total 2 marks]

4.In 1929 Edwin Hubble showed that the Universe was expanding by studying the light from stars and galaxies. Explain how.

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[Total 5 marks]

5.(a)Suggest why many stars within our galaxy do not conform with Hubbles law.

............................................................................................................

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[2]

(b)Estimate the age of the Universe, giving your answer in seconds. Show your working and take the Hubble constant to be 75 km s1 Mpc1.

age = .............................. s

[3]

[Total 5 marks]

6.Describe the important properties of the cosmic microwave background radiation and how the standard model of the Universe explains these properties. Explain their significance as evidence for the past evolution of the Universe.

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[Total 5 marks]

Lesson 60 notes - BIG BANG BIG CRUNCH?

Objectives

(c) describe qualitatively the evolution of universe 10-43 s after the big bang to the present;

(d) explain that the universe may be open, flat or closed, depending on its density (HSW 7);

(e) explain that the ultimate fate of the universe depends on its density;

(f) define the term critical density;

(g) select and use the expression for critical density of the universe

= 3 Ho2

8G

(h) explain that it is currently believed that the density of the universe is close to, and possibly exactly equal to, the critical density needed for a flat cosmology (HSW 7).

Outcomes

Be able to describe qualitatively the evolution of universe 10-43 s after the big bang to the present;

Be able to explain that the universe may be open, flat or closed, depending on its density (HSW 7);

Be able to explain that the ultimate fate of the universe depends on its density;

Be able to define the term critical density;

Be able to select and use the expression for critical density of the universe

= 3 Ho2

8G

Be able to explain that it is currently believed that the density of the universe is close to, and possibly exactly equal to, the critical density needed for a flat cosmology (HSW 7).

In the beginning

It is now generally accepted by most astronomers that the Universe as we know it began with an unimaginably huge explosion some 14 000 000 000 years (1.4x1010 years). We call this the Big Bang. The age of the universe is therefore 1.4x1010 years.

Time and space both originated at the same time with the Big Bang. Before that there was no space and no time the Big Bang created space and time. We cannot ask what happened before the Big Bang because before that moment nothing existed no space and no time!

It is interesting to compare time with distance and think of a scale where a distance of one metre represents a thousand million years. The age of the Universe is then represented by a distance of around 14m, a million years by 1 mm and one human lifespan by 0.1m!

The fascination of Cosmology is the ability to look back to the beginning of the Universe and predict what may have happened then.

Moments after the big bang

Time after the Big Bang

Nature of the Universe

Temperature

10-43 s

Grand unification epoch

10-34 - 1010 s

Electroweak epoch Quark epoch

10-10 s

Particle soup dominates

1015 K

1s

Neutrons and protons formed

1010 K

3 m

Helium nuclei formed

109 K

300 000 years

Microwave background fills the universe

6000 K

500 000 years

Temperature falls further. Infra red.

750 K

1 million years

Atoms form. Stars and galaxies exist

The universe becomes transparent

1 billion (109) years

The first stars. Heavy elements form.

18 K (-255 C)

15 billion years

The present day

2.7 K (-270.3 C)

The Big Bang - the beginning of the Universe

As thousands of years passed the Universe cooled from the initial enormous temperatures of the Big Bang (some 1015 K).

At some time in the past, roughly 500 000 years after the Big Bang the Universe became dark. The radiation emitted had passed over the barrier between visible and the infra red. From then there was no light until the primeval matter had condensed into atoms and these had slowly grouped together under gravitational attraction to make the embryo of a star. Eventually the temperature in the centre of these stars had become high enough for nuclear fusion to take place - the first star was born and blazed out into the darkness of space - there was light!

The fate of the Universe closed, flat or open

The fate of the Universe depends on how much matter there is.

Using the Hubble constant H = 70 kms-1 Mpc-1 we have found that the critical density for the Universe is 9.2x10-27 kgm-3. Now actual measurements suggest a density if some 4x10-28 kg m-3. This is too low to prevent a run-aw ay expansion but astronomers believe that a large amount of the mass of the Universe exists as "dark matter", much of which has so far been undetected.

We define a quantity called where:

The quantity = Actual average density of matter in the Universe/Critical density of the Universe The critical density will decide whether the Universe is:

(a) open a run-away expansion (1)

Critical density of the Universe

The Hubble constant (H) is also important in predicting the ultimate fate of our universe, related to the concept of its critical density.

The velocity of recession of a galaxy can be considered as its escape velocity from the rest of the Universe

By Hubbles formula:

Velocity of recession (v) = HR where R is the distance of the galaxy.

But the escape velocity is given by the formula:

Escape velocity (v) = ([2GM/R] so v2 = 2GM/R

where G is the gravitational constant (see Gravitation section)

Therefore:

v2 = 2GM/R = [2G4/3]R3]/R = 8/3[GR2 ]

But from the first equation v2= H2R2 and so:

[We have assumed both constant v and a constant value of the Hubble constant (H) in this simplified calculation.]

If the density of the Universe is greater than this the universe will contract, if it is less it will expand for ever!

Lesson 60 questions

Name

( /38)%..

Class..

MOST

1.Explain why our understanding of the very earliest moments of the Universe is unreliable.

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[Total 2 marks]

2.The future of the Universe may be open, closed or flat. Explain the meaning of the terms in italics, using a graph to illustrate your answer.

size measure

of Universe

age of Universe

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[Total 4 marks]

3.Some Cosmologists have estimated that as much as 90% of the total mass of a galaxy is made up of gas, referred to as dark matter.

(i)Suggest the nature and origin of this gas.

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[2]

(ii)The precise amount of dark matter in the Universe is unknown. Explain how the presence of dark matter affects the average density of the Universe and thus has a role in determining the ultimate fate of the Universe itself.

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[4]

[Total 6 marks]

4.Describe and explain two pieces of evidence which suggest that the Universe did in fact begin with a big bang.

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[Total 5 marks]

5.The ultimate fate of the Universe is not yet clear. The figure below shows a graph where the size of the Universe is represented from the big bang B to the present day P. The graph has been extended into the future by the dotted line ( ).

0

B

P

time

size

measure of

Universe

(i)Calculate a value for the age of the Universe in years. Assume the Hubble constant to be 75 km s1 Mpc1.

age = .. years

[3]

(ii)Describe and explain what final fate for the Universe is represented in the figure above.

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[2]

(iii)The mass of the Universe may be significantly greater than that assumed in the first paragraph of this question.Taking this to be case, sketch a second graph on the figure above using the same scales to show the future evolution of the Universe.

[2]

(iv)Comment upon the implications of your graph for the future of the Universe.

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[1]

[Total 8 marks]

6.Describe how the fate of the Universe depends upon its mean density and explain why this ultimate fate is not yet known.

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[Total 5 marks]

7.The future of the Universe may be open, closed or flat. Explain the meaning of the terms in italics, using a graph to illustrate your answer.

age of Universe

'size measure'

of Universe

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[Total 4 marks]

8.Why is our understanding of the very earliest moments of the Universe unreliable?

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[Total 2 marks]

9.The mean density of the Universe, 0, is thought to be approximately 1 1026 kg m3.Calculate a value for the Hubble constant H0.

H0 = ...........................s1

[Total 2 marks]

EMBED Word.Picture.8

Surface temperature (K): 40000 20000 10000 6000 4000 3000 2000

White dwarfs

Sun

Red giants

Red supergiants

Main sequence

Spectral type: O B A F G K M

Luminosity

(Sun = 1)

10000

1000

100

10

1

10-1

10-2

10-3

10-4

Absolute magnitude

-5

0

+5

+10

+15

Mass > 3 solar masses

Surface temperature (K): 40000 20000 10000 6000 4000 3000 2000

White dwarfs

Sun

Red giants

Red supergiants

Main sequence

Spectral type: O B A F G K M

Luminosity

(Sun = 1)

10000

1000

100

10

1

10-1

10-2

10-3

10-4

Absolute magnitude

-5

0

+5

+10

+15

Figure 1

Figure 2

Mass < 3 solar masses

Sun

Centauri

Distant stars

Distant stars

Earth

Earth

Parallax

Parallax

2

Figure 1

One second of arc

One parsec

Radius of Earths orbit

Earth

Sun

Figure 2

Brightness

Radius

Period

Figure 3

Luminosity (Sun = 1)

106

104

102

1.0

-2.0 -1.0 0.0 1.0 2.0 3.0log period (days)

Population I Cepheid variables

Population I Cepheid variables

0.1 1 10 100

Period (days)

Absolute magnitude

-5

-4

-3

-2

-1

0

+1

Figure 4

Light waves stretched Red Shift

Light waves squashed Blue Shift

Galaxy receding

Galaxy approaching

Bootes

Hydra

Corona Borealis

Velocity 61 000 kms-1

Velocity 39 000 kms-1

Velocity 21 400 kms-1

We now have a linear relationship which has proved very useful while posing some strange conundrums (conundra?!)

How do we account for the galaxies receding faster the further away they are?

Does this point to a time aeons ago where all the galaxies were in one place?

Closed Universe the Big Crunch

Flat Universe expansion but slowing

Open Universe continued expansion

Radius of the Universe

Time since the Big Bang

One galaxy escaping from all the rest

Mass of the rest of the Universe (M)

Critical density = 3H2/8G

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