Quasi-Stellar Objects (Quasars)
Quasi-Stellar Objects (Quasars)
If you look at the Andromeda Galaxy tonight (assuming it's visible), you are looking at a galaxy that is 2.3 million light-years away. The light that reaches your eye left the galaxy 2.3 million years ago, so in a sense, you are looking at the galaxy when the Universe was 2.3 million years younger. That's a short time on cosmic scales, but what about the farthest objects we see that are billions of light-years away? At that distance, even galaxies become too dim to see easily.
In 1960, astronomers discovered mysterious, starlike objects that emitted radio waves. Previously, radio light was observed from clouds of gas or supernova remnants in our Galaxy, but this was the first instance in which radio light emanated from what astronomers thought was a star. Everything about the object was strange; even its spectrum was unrecognizable. Two years later, a second similar object was discovered, and in 1963 astronomers realized that they were looking at the familiar hydrogen spectral lines. But the lines were shifted toward the red end of the spectrum by 16%, the largest shift to the red that had been observed to date.
This shift of light into the red is called redshift, and it is a measure of the speed with which an object is moving away from us. Like a train whistle that changes pitch as the train pulls away from us, light is Doppler-shifted to the red (or blue) end of the spectrum if the object is moving away from (or coming toward) us.
Forty years later, astronomers have deduced that these quasi-stellar objects, or quasars, are just tremendously bright galaxies. The energy source responsible for this incredible luminosity is the heating and colliding of gas as it spirals into a supermassive black hole at the core. A quasar, then, is just a galaxy with a supermassive black hole at its core, generating immense amounts of energy hundreds of times more luminous than the Milky Way.
Just as we see a slightly earlier Universe when we look to Andromeda, we see a much younger Universe when we look at quasars, which lie billions of light-years away. Could the active quasars represent an era in the earlier Universe when all galaxies were more active and luminous? Astronomers are answering these questions as they study the origin of our Universe.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott