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Galaxies and Beyond |
Galaxies are large groups of stars held together by gravity. The stars move and orbit the center of the galaxy. A galaxy may contain around 200 billion stars. Galaxies are classified by their shapes. Spiral galaxies have a whirlpool-like shape with a lot of dust. Elliptical galaxies have a football or basketball shape with very little dust. Irregular galaxies do not have a recognizable shape. The galaxy our solar system is in is a spiral galaxy called the Milky Way. Our solar system is located on one of the spiral arms of the galaxy.
We know that galaxies are moving away from each other by studying the color shifts of light in the electromagnetic spectrum. Galaxies move away from each other because the space between the galaxies is expanding. The increase in wavelength due to space expanding is called expansion redshift.
According to the big bang theory the universe has been expanding ever since it was first created from an extremely tiny, dense atom at a high temperature. The temperature and pressure produced an explosion that sent matter out in all directions. As the matter cooled it formed clumps that became stars and galaxies and even our solar system.
Some objects in the solar system shine brighter than trillions of Suns. They are quasars. A quasar is an extremely bright and distant high-energy source. Their distance from the Earth means that quasars are very old. They may be early stages of galaxies or connected to black holes.
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