Active Galaxy Pop-Up Text
Active Galaxies
A galaxy is a spinning collection of stars, gas, and dust held together by gravity. A typical galaxy has billions of stars, and some have trillions of stars. Galaxies come in many different shapes, but what they are made of and how they are held together is the same for all of them.
Most galaxies have a dense core of stars at the center. In the core the stars are very close together. In some galaxies, the core is so bright that it shines with the power of trillions of suns. These are called active galaxies. It is believed that a supermassive black hole is at the center of these galaxies. Active galaxies are so bright they can be seen clear across the visible universe.
Orbiting around the core of the galaxies are millions of other stars and a lot of matter in the form of gas. The matter swirling around the black hole forms a disk of material that glows brilliantly because it is heated by friction and other forces inside the disk. Surrounding the disk is a doughnut-shaped ring of gas and dust called the torus. The torus is very thick. The inside part glows brightly because it is heated by the matter around the black hole. But because it's so thick, it's cold and dark on the outside.
In some active galaxies, jets of very hot gas move away from the core on either side of the galaxy at extremely high speeds, almost at the speed of light. These jets look like long, narrow tubes or cones that are perpendicular to the disk. The jets eventually slow to a stop because of friction with gas that lies outside the galaxy. When this happens, the jets billow out to form giant clouds of matter.
GLOSSARY
- Active Galaxy: a galaxy with a super-massive black hole at its center that is sending out huge amounts of energy from a tiny core region.
- Black Hole: an object so small and dense (tightly packed together) and with gravity so strong that nothing, not even light can escape it.
- Core: the central part of a galaxy. Most galaxies have a supermassive black hole in their cores.
- Galaxy: a giant collection of stars, gas, and dust held together by their own gravity.
- Jets: thin beams of matter and energy that look like long, narrow tubes
blown out of the center of an active galaxy.
- Supermassive black hole: a black hole that has millions or billions of times the Sun's mass.
- Torus: a doughnut-shaped object. In an active galaxy, a doughnut-shaped ring of gas and dust orbit the central black hole.
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