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10. Stars and galaxies
| 10.11 |
Galaxy properties
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| Like all form in the Universe, the vast majority of galaxies into a few common shape patterns, that then vary according to size and general features such as rate of change of position, rotation rate, distance, general attraction or repulsion to or from other galaxies. | ||
| The most common shape varieties of galaxies | ||
| The four main classes of galactic shapes are: | ||
| (1) Spiral |  |
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| These galaxies resemble pin wheels, with spiral arms trailing out from a brighter centre. The largest galaxies appear to be Spiral in shape and almost always have companion smaller galaxies ( sometimes called pygmy galaxies). | ||
| (2) Barred spiral |  |
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| Here the spiral arms trail from the ends of a central bar around 30% of galaxies are spirals or barred spirals. All barrel spiral galaxies are in pairs, with the barrel effect being created from the gravitation pull of the second galaxy. | ||
| (3) Elliptical | |
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| These galaxies do not have spiral arms. About 60% of galaxies are elliptical, varying in shape from almost spherical (like a soccer ball) to very flattened (like a football). Elliptical galaxies are usually very small, and most often the "pygmy" type galaxies that cluster around much larger galaxies. | ||
| (4) Irregular |  |
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| About 10% of galaxies are irregular with no definite shape. | ||
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