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Quasars & Active Galaxies
Quasars are peculiar objects that radiate as much energy
per second as a thousand or more galaxies, from a region
that has a diameter about one millionth that of the host galaxy. It is as if a
powerhouse the size of a small flashlight produced as much light as all the
houses and businesses in the entire L.A. basin!
Comparison of a normal galaxy, active galaxy and quasar.
Quasars are intense sources of X-rays as well as visible light.
They are the most powerful type of X-ray source yet discovered. Some quasars are
so bright that they can be seen at a distance of 12 billion light years.
The power of a quasar depends on the mass of its central supermassive black
hole and the rate at which it swallows matter. Almost all galaxies, including
our own, are thought to contain supermassive black holes in their centers.
Quasars represent extreme cases where large quantities of gas are pouring into
the black hole so rapidly that the energy output is a thousand times greater than
the galaxy itself.
A galaxy with a somewhat less active supermassive black hole is called an Active Galaxy and
its black hole is
called an "Active Galactic Nucleus" or AGN. Our Milky Way
Galaxy and our neighbor, the Andromeda Galaxy, are examples of normal
galaxies, where the supermassive black hole has very little gas to capture.