Education Activities To Accompany Chandra Data Analysis Software 3C273
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] Click
Here for the Solution Click
Here for Detailed Hints
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. Click
Here for the Solution Click
Here for Detailed Hints
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]
