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Section I: Introduction
Section II: 6 Activities
Section III: Summary

Education Activities To Accompany Chandra Data Analysis Software

Faster Than a Speeding Bullet…

3C273 Optical Spectrum
Radio "map" of 3C273
larger image
It is hard to convey the excitement that the discovery of the quasars generated in the early 1960's. Maarten Schmidt's picture even appeared on the cover of TIME magazine. But there was much skepticism regarding their true nature as well. Not only were the energy requirements enormous if the quasars were really distant objects, but something else was observed in the 1970's that made the whole puzzle even more unbelievable. It seemed like some material in the jet was moving at 6 times the speed of light, which violated all our ideas about the nature of time and space. Look at the following radio "map" of 3C273 taken by researchers at the Owens Valley Radio Observatory and the National Radio Astronomy Observatory.

Look at the little blob of material that is moving outward. It appears to change its position by .002 arc-seconds in 3 years.

Activity 6: How fast is the jet material moving?
  1. How far has the blob in the figure appeared to have moved in three years?
    Click Here for the Solution
    Click Here for Detailed Hints
  2. What must its velocity be for this to be true?
    Click Here for the Solution
    Click Here for Detailed Hints

    This result clearly violates basic laws of physics. Light, which moves at the constant known as the speed of light, represented by c, is the fastest that light can travel, making one light year, the distance that something moving at the speed of light would cover in one year, the distance that light must travel in one year. So how do we explain the observation?

    How can this be? Several models have been proposed, but the most likely idea has the blob moving not across our line of sight, but rather almost along it. But this seems even more preposterous, because it would have to move even further to get to the position we observe! However, the state of affairs is easily seen with the aid of the following diagram.

    3C273 Optical Spectrum

    Imagine that the blob emits the photon (Photon 1) that we see at the top of the radio map at point O. It starts traveling the enormous journey in a straight line towards Earth, and the photon reaches point B after 100 years. Thus, B is 100 light years from O. Meanwhile, the blob, moving at almost the speed of light in the direction of A, gets to A after 101 years. At A, the blob emits a photon (Photon 2), as it has been doing all along, of course, toward the Earth. This second photon also travels in a straight line towards earth. Photon 2's path is parallel to photon 1's path, while the actual source (ie "blob") continues on its own path at the angle shown in the diagram. At this point, by looking at the triangle OBA, the blob appears to be 8 light years from B. But the photon emitted from the blob at A is actually only one year behind the original photon observed at B. So from the point of view of the Earth, the blob appears to emit light originally from the direction toward B, and once that light finally gets to us, after billions of years, the light from A will be one year behind.

Our model is saved! But how the jet get formed to begin with? [next] [back]

Last updated: 03/21/08


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