Galaxies

=The Galaxies - //' To Infinity and Beyond'//=


 * Below is an image from:** [|**http://shareme.com/images/large/Free_Galaxy_Screensaver-2579.jpg**]

A galaxy is a group of millions of stars, dust and gas held together by gravity. Galaxies are scattered throughout the universe. As far as scientists know there may be 100 billion galaxies!!! Galaxies range in their diameter from around 9 trillion killometers to about less than a billion km.

Scientists classify galaxies into the following group:


 * Spiral:** A spiral galaxy is shaped like a disc with a bulge in the centre. Clouds of dust and gas lie throughout the disc. Spiral galaxies are rich in gas and dust particles, which is often visible layers of dust when viewed from the top or bottom. The Milky Way falls under this category.

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Elliptical galaxies varies in different shape from round to flattened globes. A the name says it, elliptical means that the shape could either be flat or spherical. The light from an elliptical galaxy is brightest in the centre and gradually becomes fainter toward its outer region where the bright ness of the light is quite dull.
 * Elliptical galaxies:**

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A barred spiral galaxy is exactly like a spiral galaxy: it is shaped like a disc without a bulge in the centre. Instead of a bulge it has a bar shaped structure as its nucleus. Bar galaxies are not that common but there are many stiil to be discovered.
 * Barred Spiral Galaxies:**

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Irregular galaxies are very rare. It does not have any lines of symmetry. One way irregular galaxies are formed is when galaxies collide or come close to one another, when this happens their gravitational forces interact and thus an irregular galaxy is formed.
 * Irregular galaxies:**

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The Andromeda galaxy is the biggest galaxy of those which are near the Milky Way. It has twice as many stars as the Milky Way. it has a bright disc which emits 10% of the total light emitted by the galaxy. It is 2.2 million light-years away and it has a diameter of about 165,000 light-years and contains at least 200 billion stars. In its core, scientists have discovered about 500 red giants which makes the galaxy bigger than predicted. It has a diameter of 200000 light years. The Andromeda galaxy was discovered by Hubble. The Andromeda galaxy is the Milky Ways neighbouring galaxy. It is known as the 'Andromeda Spiral' / 'M31.' It covers an area of the sky which is supposedly 5 times the diameter of the Earth's moon!!! It is moving towards the Milky-way, our galaxy at the rate of 9 million kilometres per day and it it is predicted that the 2 galaxies will meet in 2.5 billion years. Scientist have discovered that the Andromeda galaxy contains two nuclei which means it has consumed another galaxy before.

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The Milky way is our home galaxy which contains the Sun, earth, the Solar System and around a hundred billion stars. It includes huge clouds of dust particles and gasses. The Milky Way is a spiral Galaxy and so the Milky Way Galaxy is shaped like a thin disc with a bulge in the centre. Stars, dust and gasses lie in the bulge of the Milky Way. The flat part of the Milky Way's disc contains many young stars which were small, irregularly shaped groups of stars which is now called galactic clusters. The bulge and disc is clustered around a cirlce of stars known as the halo. The halo contains very old stars which are heavy and spherical shaped which are called globular clusters.
 * The Milky Way:**

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The diameter of the Milky Way Galaxy is about 100,000 light-years. A light-year is the distance that light travels in one year--about 9.46 trillion kilometres. Therefor the diameter of the Milky way is approximately 946000 trillion kilometres!!! The Milky Way is about 10,000 light-years thick at the central bulge and much flatter toward the edges of the disc. Our solar system is located in the outskirts of the Galaxy, about 25,000 light-years away from the centre. Most scientists estimate that the total mass of the Milky Way is more than 100 billion times that of the sun most of which are in the centre.

All stars and star clusters in the Milky Way orbit the centre of the Galaxy. The clouds of dust and gases in the Milky Way Galaxy prevent us from seeing very far into its centre. However scientist still have discovered that central region gives off enormous amounts of energy. Studies with radio and telescopes have also revealed that a powerful gravitational force seems to come from the exact centre of the Galaxy. Some scientists believe that the Milky Way Galaxy's centre is a massive black hole.

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Below is an image from: [] Different galaxies give off many kinds of radiation, including gamma rays, infrared rays, radio waves, ultraviolet light, visible light rays. Scientists study this radiation with optical and radio telescopes, and other instruments. Scientists have discovered that almost all galaxies are moving away from each other at super fast speeds. In addition the galaxies farthest from the earth appear to travel the fastest. Thus most scientists believe the universe is expanding constantly. Scientists have also proposed a theory about the origin of galaxies. The Big Bang theory states that masses of gas formed soon after the universe began to expand billions of years ago. According to the theory, scientists believe that the gravity slowly condensed these masses into galaxies. No new galaxies have been formed since then, and so all galaxies are about the same age.


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