The Andromeda galaxy  


Written by: Anna-Karin Erlandsson, Caroline Norén and Helene Fherm

Teacher: Roger Andersson

The History

When it is a starry night, you can be able to see a sign called Andromeda. Next to it you can see a light spot.

I think that many of they who have lived at the Northern Hemisphere, have looked at the starry sky and wondered what this spot is.

The oldest, still extant drawing of the Andromeda galaxy is from 964 AD. It is a map of the starry sky, made by the astronomer Abderrahaman al-Sulfi.

In the 18 th century a man named Charles Messier made a list of diffuse sky objects. He called the spot next to Andromeda M31 and listed it as a nebula, because he didn’t see any stars in it.

At that time, nobody knew that there were other galaxies.

But more than one hundred years later, in 1923, Edwin Hubble started to study the “nebula”. He used a 100-inch reflector telescope and he succeeded in identify stars within it. Subsequently he discovered that there were blue stars in the arms of the galaxy. This created theories, that it was a galaxy.

In 1924 Hubble proved that the Andromeda wasn’t a part of the Milky Way. He compared luminous intensity of cepheid-variables within M31 with they in the Milky Way. He found out that they in M31 were fainter, accordingly they were farther away.

Another man, Walter Baade made further observations. He wanted to see what’s in the center of the galaxy.

He thought that the bright stars in the center were blue, because the stars in the arms of the galaxy were.

But he found out that the stars in the middle were red giants. In 1943 he succeeded in taking pictures where hundreds of stars in the middle could be seen.

When Baade directed his telescope from the center and outwards, he saw that there were blue giants in the arms of the galaxy, and there were red giants between them.

Up to now they have discovered about 300 crowds of stars within the galaxy, and the galaxy has a mass of between 300-400 billion stars. The Andromeda galaxy is twice as massive as the Milky Way.

Around the Andromeda there is eight small galaxies, most of them is elliptical and contains mostly old stars. But in some of them there is young stars, gas and dust.

Like all other spiral galaxies, the Andromeda has a stellar disk with young stars. Around this disk you can find the halo. It consists of older stars; most of them is situated in crowds.

In the galaxy, there are lots of ball-shaped crowds of stars.

Two men from Japan, Yoshihiko Satio and Masanori Iye studied these crowds of stars, and they suspect that the Andromeda has swallowed another galaxy.

The Japanese examined the content of metal in the stars. The found out that the content of metal falls off from the middle and out. That was natural, because the stars in the middle have been formed of material that has been part of previous stars.

But they discovered that there were more crowds of stars with a medium content of metal, than they expected. This indicates that these crowds of stars have had a different development than the others.

The Japanese examined the way these stars move in the galaxy. They found out that the stars that is less than 20 000 light-years away from the nucleus rotated normally.

  The stars that were further away from the nucleus rotated more or less random. And it was just this special kind of stars that rotated randomly.

Satio and Iye’s theory is that the Andromeda galaxy collied with a smaller galaxy, when it was still young.

The Andromeda has two nucleuses in the center. The bigger one is considered to be the real nucleus, and the smaller one is a rest of the galaxy that collided with the Andromeda.

Quite recently they have found a warp in the stellar disk of the Andromeda. This is the most serious case of warp in a spiral galaxy that we know about.

A possible explanation is the eight galaxies around the Andromeda. They can be able to affect the stellar disk with their gravity.

The first observations were made with a big digital camera. It showed that the inner part of the stellar disk was an almost perfect ellipse. But the form is more irregular in the outer parts.

The whole galaxy is faintly S-shaped, one side bends upwards and the other bends downwards.  


The Present

The Andromeda galaxy is definitely that galaxy which we on Earth have studied most 1.

One of the reasons to that is that it is our closest, large galaxy.

   Together with the Milky Way and about thirty other smaller galaxies it forms the "Local group".

    Another reason to why it has been studied so much is that it is quiet similar to the Milky Way. Just like our own galaxy it is a spiral galaxy of the type Sb.

The Andromeda galaxy has a diameter of 200.000 lightyears 1 , which is about double so long compared to the diameter of the Milky Way. The mass of the  Andromeda galaxy is 3-4 * 10 11 solarmasses 1 , which is about double as much than the mass of our galaxy.

    The Andromeda galaxy consists of about one trillion of stars 2. Around the galaxy circling more than ten, smaller galaxies; so-called satellitegalaxies 1. The two biggest satellitegalaxies are called M32 and M110.


M32 3

  Because of the interaction between M32 and the Andromedagalaxy the structure of the Andromeda galaxy’s arms is disturbed. In the areas that are closest to M32 it is hard to discern where the arms begin and end 1.

    Something interesting with the Andromeda galaxy is that it seams to be two nuclei 1. About that the scientists have two theories:

    The first one is that the Andromeda galaxy has eaten up a smaller galaxy which has coming in it’s way.

The second theory is that the two nuclei in fact are one large nucleus, which on some spots is darkened by some dark materia so that it looks like two nuclei.                         


The two nucleus 4

    Another exciting thing with the galaxy is some early data from the Hubble-telescope. X-rays reveals that it may be a black hole-candidate in the nucleus of the Andromedagalaxy. The black hole weight about 30 millions solarmasses and has a

temperature of one million degrees, which is very cold for a black hole.


An X-ray picture. The blue spot is the black hole. 5


The Andromeda galaxy has an absolute magnitude of –21, but because of the distance between the Milky Way and the Andromeda galaxy, which is about 2,9 million lightyears 1 , the apparently magnitude is not more than 3,4. However this is enough for us to see it without a telescope. If you would like to see it, you shall look at the constellation Andromeda, where it appears as a faint lightspot.

1.        The fact is taken from

2.        The fact is taken from the work of reference “Stora Focus”

  1. The picture is taken from
  2. The picture is taken from
  3. The picture is taken from

The Future

The Andromeda galaxy is approaching our own galaxy, The Milky Way, with a speed about 300,000 miles per hour (m/h taken from an article by James Gatlin).

What we still do not know is whether the Andromeda galaxy has a head-on-collision in store or a just simple touch by the side. Astronomers are trying to find that out at the moment, by deciding Andromeda's tangential motion across the sky.

If the Andromeda galaxy were to hit us straight on, the Milky Way wood sees to exist, and the pinwheel galaxy we call home would together with Andromeda create an enormous elliptical galaxy.

But this would lie very, very far in the future, approximately 5 billion years. Since we know that the Sun has an estimated time to burn, it is not shore if the Sun still is alive at this time. If not Earth will be a cold, lifeless rocky planet. Perhaps the human raze has found another planet to live or has colonized a space station.

The collision in hand would take several billion years to run its course, so even if humans have a new planet it will be really hard to understand what it is that is happening.

By studying other collisions in space and by using computers astronomers have the possibility to assemble a few snapshots of the collision and have a small preview of what might happen to our own galaxy.

Rules to ”A trip to the Andromeda galaxy”

We think this game is for people that are ten years old or elder.

  • Playingpieces
  • 1 die
  • questioncards
  • 1 playingboard
  • All the players throw the die. That player that got the lowest number of dots begins.
  • He/she throws the die; 1 and 2 =1 step forward, 3 and 4 =2 steps forward and 5 and 6 = 3 steps forward. Go so many step that the die shows.
  • Then the player at the left side of the first player takes a quetsioncard and read it. The first player shall now answer the question. If he/she gives the right answer he/she shall go two steps forward, but if he/she give the wrong answer he/she musts go two steps back.
  • Then it is the player’s at the left side of the first player turn to throw the die.
  • Like that it goes until one of the players reaches the Andromeda galaxy and by that wins the game.

Remember to look out for the Asteroid-belt and black holes!

Questions to ”The trip to the Andromeda galaxy”

1. What is the Earth called with another           name?

  Answer: Tellus

2. Which galaxy is the Andromeda galaxy coming closer to?

Answer: the Milky Way

3. Say all the planets in our solar system.

  Answer: Mercurius, Venus, Earth, Mars, Jupiter, Saturnus, Uranus, Neptunus and Pluto (not necessarily in that order)

4. What is an object’s brightness called with another word?

Answer: magnitude

5. Between which planets in our solar system is the Asteroid-belt situated?

  Answer: Mars and Jupiter

6. What is the Andromeda galaxy called with another name?

  Answer: M31

7. What is the sun for kind of object? 

    A. a planet  B. a star  C. a comet

    Answer: a star

8. Which is the closest star to the  Earth?

  Answer: the sun

9. If you are travelling in the space,  what are you travelling in/on?

  A. a spaceship  B. a bike  C. an aeroplane

  Answer: A

10:What are the Large Magellanic Cloud and the Small  Magellanic Cloud?

A. Galaxies  B.nebuloses

Answer: A

11. What is a telescope?

  1. large binoculars  B. a telephone

C. glasses

     Answer: A

12. When was the Universe formed according to the “Big Bang”-theory?

A. for 15.000 years ago  B. for 15 million years ago  C. for 15 billion years ago

  Answer: C

13. What is our galaxy called?

  Answer: the Milky Way

14. How far is it to the Andromeda galaxy?

  A. less than 10 miles B.10 miles

  C. more than 10 miles

  Answer: C

15. Which is the visual brightness of   the Andromeda galaxy?

  A.-3,4 B.3,4 C.9,6

  Answer: B

16. What is a shooting star?

      Answer: a meteor

17. Which element is most common on Earth?

  A.oxygen  B.hydrogen  C.carbon

  Answer: A

18. Which element is most common in the space?

  A.oxygen  B.hydrogen  C.carbon

  Answer: B

19.Which galaxy was discovered first?

  Answer: the Andromeda galaxy

20. Which of this galaxies is a satellitegalax to the Andromeda galaxy?

  A. LMC B. SMC C. M32

  Answer: C

21. What calls that diagram that shows the development  of the stars?

  Answer: the HR-diagram ( the Hertzsprung-Russell-diagram)

22. What calls that spherical structure that surrounds a galaxy?

  A. halo B. shell C. envelope

  Answer: A

24. How many days does Mars need to get travel once around the sun?

  A. 187 B. 687 C. 387

  Answer: B

25. Which one of the planets has a big, red spot?

  Answer: Jupiter

26. How many planets are there in our solar system?

  Answer: 9

27. What kind of Galaxy is the Andromeda galaxy?

  Answer: A Spiral Galaxy

28. What does a comet consist of?          

  Answer: Ice

29. Roughly, how old is the sun?

  Answer: 5 billion years

30. Who discovered that M31 is a galaxy?

  A. Albert Einstein B. Bill Clinton C. Edwin Hubble

Answer: C

31. Does Pluto have any moons?

Answer: Yes (Charon)

32. Is Andromeda bigger then our galaxy?

  Answer: Yes

33. What is a light-year?

  Answer: It’s the distance that the light travels during one year

34. How many moons does Jupiter have?

  A. 16 B. 4 C. 82

  Answer: A

35. What colour does a very hot star have?

Answer: Blue

36. Where on the Earth do you have to be to see the Andromeda galaxy?

  Answer: The northern hemisphere

37. A supernova, what is that?

  Answer: An exploding star

38. What happens during a solar eclipse?

  Answer: The moon passes between  the Earth and the Sun

39. What is dark matter?

  Answer: Matter that doesn’t emit any light

40. Which of the planets in our solar system is the smallest (in size)?

  Answer: Pluto

Our own thoughts

We chosed to work with the Andromeda galaxy because we wanted to know more about it. We found a lot more information about it then we believed we would do.

We didn’t just learn about the Andromeda galaxy but also about our own galaxy, the Milky Way, and about space in general.



Work of reference - Stora Focus couldn’t find the ISBN number

Stjärnhimlen, en utförlig astronomisk guide –  Robert Burnham- Köneman

ISBN: 3829055072

På resa i universum, galaxerna – Lademann couldn’t find the ISBN number

Historian om Hubble-teleskopet, universum i fokus – Stuart Clark ISBN: 9151833891

Vetenskapens värld, universum – Ian Nicholson, Patrick Moore couldn’t find the ISBN number


The Internet:


We searched at nasa's homepage and at

Written by: Anna-Karin Erlandsson  Nv2a

                  Helene Fherm  Nv2c

                  Caroline Norén  Nv2c


                  Roger Andersson Teacher

                  Västerhöjdsgymnasiet, Skövde, Sweden