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

Education Activities To Accompany Chandra Data Analysis Software

The Care and Feeding of Quasars

The most plausible explanation for these most implausible objects appears to be, oddly enough, similar to models that exist for binary X-ray stars in our own galaxy. The idea is that matter under the influence of an intense gravitational field loses energy and releases enormous quantities of radiation in the process. Just as water goes over Niagara Falls, losing its potential energy while providing us with power to drive electric generators, so can material fall into a stellar gravitational field and emit light.

Currently, the most popular model is that material near the quasar falls into a black hole. But doesn't a black hole swallow everything around it? This is a very common misconception, and the answer is no. Only material very close would inevitably be sucked into this type of object. In fact, if the Sun were suddenly to become a black hole, the orbit of the Earth would not change at all.

How much energy is released depends on the strength of the gravitational field, and how much mass is fed into the hole. (The black hole really doesn't have a surface, but the material continues to yield energy to the outside world until it passes a place known as the Schwarzschild radius, named after the German astronomer who worked out its properties nearly a century ago.)

Activity 5: How can we get the vast quasar energy from a black hole?

1. The Schwarzschild radius (RS) is the minimum distance from the center of a black hole (or any other object for that matter) that an object must be the gravitational force of the black hole to guarantee that the object will collide with the center of mass of the black hole. Assuming that the attracted mass's gravitational potential energy can be approximated by E = Gm1m2/R, determine the magnitude of the Schwarzchild radius (use CGS units) for a black hole of 109 solar masses.
[Note: G = 6.7 x 10-8]
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2. We can estimate the energy output of the black hole by determining the gravitational potential energy lost by a mass m as it travels towards the black hole. Let's say that a mass equal to that of our sun is located an infinite distance from a black hole of 109 solar masses. Over one year, mass m is gravitationally accelerated to RS of the black hole. If the black hole has only accelerated mass m, how much energy does the black hole emit?
Assume that the gravitational potential energy of the planet can be approximated by E = Gm1m2/RS.
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Thus, our picture becomes this: an intense gravitational field provides the pull that sweeps about one star the size of our Sun each year into its confines. The energy released provides the x-rays, radio waves, and optical light that we see coming from the quasar. The variability is explained by the small size of the object; even though it shines more brightly than hundreds of entire galaxies, it occupies a volume no larger than our solar system.

But lest we rest on our laurels, 3C273 had yet one more trick up its sleeve, one that threatened to wreck this entire model [next] [back]

Last updated: 04/04/08


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