Education.com
Try
Brainzy
Try
Plus

Quasars Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 18, 2011

How Distant?

The sizes of the quasars, as well as estimates of their energy output, have been determined according to the Hubble relation between red shifts and distances. All quasars show significant red shifts in the absorption lines of their spectra. This has led most astronomers to surmise that they are billions of light-years away from us.

Suppose, however, that the red shifts are being misinterpreted? Are quasars actually local objects of modest size that are thrust outward from the nucleus of our galaxy at tremendous speeds? This is an interesting theory, but it is not widely accepted. If quasars are being ejected from our galaxy, then it is reasonable to suppose that they are ejected from other galaxies too. In such a case, some of the quasars ejected from other galaxies should be observed as approaching us. This would give such objects a pronounced blue Doppler shift. However, no quasar has ever been found that exhibits a blue shift in its spectral lines.

Another attempt has been made to prove that quasars are “local.” Albert Einstein showed, in the formulation of his general theory of relativity, that a powerful gravitational field can produce a red shift in the spectrum of the light coming from the source of the gravitation. This effect has been observed and measured, so scientists know that Einstein’s theory is correct. Can the red shifts in the spectral lines of quasars be explained in terms of the relativistic effect of gravitation? A super dense object with extreme gravitation near its surface could produce a large red shift. This remains an open question. Still, an affirmative answer would not constitute conclusive proof that quasars are “local.”

Recent observations of quasars using the HST have begun to resolve the riddle. Evidence is accumulating to support the theory that quasars are among the most distant objects we can see in the Cosmos and that they therefore present a picture of the Universe as it was when it was much younger than it is now. This gives astronomers a way to look back in time to whatever extent they want simply by observing galaxies and quasar objects at various distances as indicated by their red shifts.

A severe blow was dealt to the local quasar theory when scientists calculated that the first quasar that was discovered, called 3C4S , would have to have a mass the same as the Sun, be only 10 km (6 mi) in diameter, and be in the Earth’s atmosphere in order to account for the radiation intensity it possesses. Even if 3C4S has thousands of times the mass of the Sun, calculations show that it still must reside within our Solar System, and this obviously is not the case. The derivations in these terms for other quasars give similar results.

The determination of the distances to quasars represents a good example of the devil’s-advocate method of lending support to a theory by discrediting all its plausible refutations. The quasars, even after attack by the devil’s-advocate scientific method of inquiry, appear to be distant and energetic cosmic phenomena.

View Full Article
Add your own comment

Ask a Question

Have questions about this article or topic? Ask
Ask
150 Characters allowed