Education Activities To Accompany Chandra Data Analysis Software 3C273
Of Time and the Universe
The Moving Finger Writes; and having writ,
Moves on: nor all your Piety nor Wit
Shall lure it back to cancel half a line,
Nor all your Tears wash out a Word of it. Omar Khayyam, 11th century
When the nature of the galaxies finally came to light about 75 years ago, people were awed by the serene grandeur that these "island universes" presented. Stately in their motions, rotating once every 100 million years, they presented a picture of eternal tranquility. In fact, a popular cosmological model up to the 1960’s was the Steady-State Theory, which posited an unchanging, eternal, infinite space where new and old objects stood side by side, uniformly spread together throughout the far reaches of the universe. The discovery of the quasars sounded the death knell for this idea. Indeed, the implications of these observations were so bizarre that many astronomers refused to believe the interpretation that we have just presented, and instead sought to explain the red shift (which implied vast distances and hence stupendous energy output) by other means. All these ideas failed, and rather reluctantly for many, scientists had to accept the picture we have painted here.
When hundreds of other quasars were found, one fact stared us in the face: the nearest quasar remained 3C273, some 2.5 billion light years away from us. Where were the more nearby ones? Why weren't they distributed uniformly in space?
The answer seems clear: the quasars evolve in time. Remember that we see 3C273 as it was billions of years ago because of its incredible distance. Thus, if a nearby quasar once existed, say, in M31, we would be seeing it as it was a mere million or so years ago. But suppose the quasar turns into a galaxy after a while. If quasars were a product of the early universe, only the most distant ones would be visible, since we would be looking at them at a time when they were active. So it is quite possible that if someone were to observe our Milky Way from close to 3C273, they would see our galaxy as a quasar, since the light from the Milky Way would be 2.5 billion years old! And from their vantage point, 3C273 would be a nearby, and quite possibly normal, galaxy.
So quite literally, the quasars are cosmic time machines, leading us back into the early history of the universe, which is quite different from the regions of space that we see today in our neighborhood. They portray a story of vast storehouses of energy that seethe in x-rays, opening our eyes to the cosmic history that is part of our common heritage.
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