Galaxies

Introduction

The stars are not scattered about the universe in an accidental way. They are grouped in galaxies. All the stars we can see at night take part of our milky way. There are billions of galaxies in the universe. And each galaxy consists of milliards of stars. Most galaxies radiate light continuously, but you also have galaxies which are more active… More about this, in this part of our homepage.

General information

When the moon is not shining at night then it is possible to see a fluffy strip of light. This is a galaxy. Through a telescope you can see that a galaxy consists out of a lot of stars, that is some milliards of stars (of course the galaxies differ among themselves). These stars seem to be packed up closer together. This only seems so, because the galaxy is so endlessly far away from us.

The shape

A galaxy looks like a rather flat disc with a swelling in the middle. (Click here for a picture)

The milliards of stars in the galaxy are scattered over the disc. The whole galaxy turns around the centre but not all at the same speed. The stars which are close to the centre are moving faster than the stars which are on the edge of the disc.
The galaxies can be classified according to their real veritably shape. Roughly spealing there are two shapes: spiral and elliptic. Our Milky Way is spiral shaped. All the other spiral systems have almost the same shape, structure of stars, groups, gasses and matter. However, close to the galaxy Adromeda, one of our "neighbours" in the universe, there are two much smaller galaxies. These are elliptic galaxies and it is striking that they mainly consist of old stars, while spiral systems have more young stars.

Active galaxies

There are some galaxies, which do not belong to a certain group. These have often a spiral shape and have special characters. An example is the galaxy "Wheel", of which the centre s lost by a collision.

There is also a type spiralshaped galaxies, with a very bright kernel and weak shining arms. Carl Seyfert was in the 40's the first who has studied these galaxies. That is why these galaxies are called the galaxies of Seyfert. Because the centre of these galaxies are so bright, some people can think it are stars.

The galaxies of Seyfert have a very powerful source of energy in the centre. But there is also another type. These are called radiogalaxies, so-called because they send out radiowaves very powerful. These radiowaves do not come from the centre, but from the double lobs, spaceareas on both sides of the galaxy. The diameter of the lobs reacht out for more lightyears then the galaxy himself.

Groups of galaxies

Just like the stars in the universe form groups in galaxies, so do galaxies form groups. For example: our Milky Way is situated rather close to two other galaxies. These three galaxies belong to a group of about 30 galaxies, which is called the Local Group.
This group contains three big spiralshaped galaxies: The Milky Way, M33 and Andromeda. M33 is situated 2,4 milllion lightyears away from us, about 200.000 lightyears further as Andromeda.
Two of the little ellipticshaped galaxies are encircled by millions of stars. These are spherical groups.
The only big ellipticshaped galaxy in the Local Group, Maffei I, has probable the same weight as the Milky Way. This galaxy is situated 3,3 million lightyears away from us.
The Local Group is a rather small group of galaxies. The closest bigger group contains 1000 to 2000 galaxies. The centre is the powerful active galaxy M87.
Most groups contains around the 100 to 400 galaxies.

Quasars

This part is about quasars. It is a very complex subject, but we have tried to explain it as simply as possible.

Quasars looks like foggy blue stars of which the radiation of light varies greatly. The quasars also radiate very powerful radio signals. This is the more striking because these quasars radiate more radio signals than normal galaxies and this leads to the presumption that these bodies are very big. But the highly varying radiation of light proves that the diameter must be much smaller than that of an average galaxy. So the quasars are (relatively) very small (about the size of a solar system), but they radiate the energy of hundreds of galaxies together.

Now the question is, what power supply is the cause of this. There is only one possible solution, and that is a gigantic black hole. A black hole comes into being when old stars completely collapse. It is an area in space with very high gravitation, that absorbs all the matter like a cosmic hoover. A black hole is surrpunded by a very fast turning disc of hot gas. The matter that is attracted by the gravitation, absorbs very much energy. This energy is released again when the matter finds its way through the black hole.

Big Bang | Stars | Nebulas | Galaxies | TMR-1C