FREE ESSAY ON QUASARS AND ACTIVE GALAXIES

QUASARS AND ACTIVE GALAXIES

Amy A. Zeleznik
Peter Anderson
GSC 158
11 November 1999
Quasars and Active Galaxies
The astronomical world is full of phenomena beyond the average person's imagination. The
technical tools and analytical methods astronomers use are very complex. The enormous
numbers and distances are mind boggling. Theories behind astronomical phenomena are based
on yet another theory. In order to understand the concept of quasars and active galaxies,
one must first have a feel for the astronomical numbers involved. Secondly, a basic
knowledge of the tools of the trade, and finally, a working knowledge of astronomical
jargon. Once there is a working knowledge of the aforementioned factors, then there is
the chance that one could be able to assimilate the complex theoretical properties that
are used to discuss quasars and active galaxies.
In order to understand the large numbers used to express the vast distances discussed in
astronomy, one needs to relate these numbers to everyday life. During everyday
conversation, people may say things like "the national debt is trillions of dollars,"
"the lottery is up to 31 million dollars," or "John Doe is a billionaire." An astronomer
might say that "one astronomical unit equals 93,000,000 miles or that a light-year is
5,870,000,000,000,000 miles." The human comprehension level of all of these terms is
probably nowhere near the actual truth behind how large these numbers really are. To
obtain a feel for these gigantic distances used by astronomers, Astronomy Magazine
writer, John P. Wiley says it may be helpful to keep in mind that it takes thirty-one
years to count to one billion at the rate of one number per second. He also puts a voyage
to a galaxy that is a billion light-years away into perspective by calculating how long
it would take to get there in a vessel speeding along at 18,000 miles an hour. The trip
would take 37 trillion years. When discussing galaxies and quasars, billions are the
smallest numbers used (56,57). 
The theory of how quasars are created is based on the idea that the universe is
expanding. Among astronomers, the popular consensus is that the Earth is in an expanding
universe in which the laws of physics will hold true beyond this planet as well. G. Mark
Voit, an astronomer at the Space Telescope Science Institute, believes that the beginning
of the universe was a time when many galaxies would be visible to the naked eye because
the universe was more condensed than it is in present day. In the centers of many
galaxies would be radiant objects that looked like stars but seemed brighter than all of
the stars in its galaxy. Contemporary astronomers call these star-like objects quasars
and believe their presence more plentiful during the early formation of the universe
(41). A professor of astronomy at the University of Wales states that "Quasars were . . .
more prevalent in the epoch of high galaxy density, when the universe was younger and
more crowded than it is now" (Disney 57). The quasars seen today are billions of
light-years away indicating that they have already come and gone, and they no longer
exist. A galactic collision is a probable catalyst for the birth of a quasar. It is
possible that the diminishing population of quasars is due to the expansion of the
universe. Disney reports that the Hubble Telescope reveals that "about three quarters of
the host galaxies appeared to be colliding with or swallowing other galaxies" (56). As
the galaxies spread further apart, there were fewer collisions among them. The distance
provides less swirling matter and gasses, and gives the galaxy room to settle and mature.
The minimized violence of collisions during galactic evolution is theoretically related
to the decline of quasars (Disney 56,57; Peterson 60; Voit 42).
Stephen Hawking's Universe shows that initial quasar discovery was dependent on a
combination of spectroscopy and radio astronomy. A brief description of spectroscopy is
when a ray of light is split into the colors of a rainbow through a spectrum, energy is
emitted or absorbed by the colors. Astronomers use the spectra of light to determine
temperature, velocity, and more. The majority of astronomers believe that if the spectra
of a point of light has a significant redshift, then the object is a good candidate for a
quasar. A redshift symbolizes a motion-induced change in wavelength, indicating that an
object is very far away, and rapidly moving away from the observer's line of sight
(Chaisson 71,93). If the object is extremely distant, and can be seen as a point of
light, then it must emit an enormous amount of energy (Bartusiak 56; Disney 53). With the
use of radio astronomy, it was determined that a star named 3C273, located in the Virgo
constellation, was emitting radio waves. Normal stars, however, do not emit radio waves
(Hawking). Because of this unusual phenomenon, the visible light spectrum of 3C273 was
analyzed by Maarten Schmidt, an astronomer at the Mount Palomar Observatory in
California. He was bewildered when he found a sixteen percent redshift "due to the
expansion of the universe." The redshift indicated an object approximately two billion
light-years away. "Given the distance and the observed brightness of the object, Schmidt
calculated that it had to be emitting several hundred times more light than any galaxy"
(Disney 53,54). Through the use of spectroscopy, 3C273 was deemed a quasar rather than a
star. 
The question of how a quasar could radiate so much energy, yet be relatively small was on
the minds of astronomers and physicists. General relativists brought up the idea of
gravitational collapse as a possible explanation. A catastrophic gravitational collapse
of an object such as a star in a galaxy would cause a tremendous gravitational pull. The
name astronomers have given this particular gravitation pull or collapse is a black hole
(Hawking). The black hole is an eating machine that causes the gasses and matter within
the vicinity to "grow searingly hot and [radiate] enormous amounts of energy" (Voit 43).
Science writer, Steve Olsen describes a black hole as ". . . the most exotic things in
the universe - objects that pack the mass of millions or billions of suns into a volume
no larger than our solar system" (50). Computer simulations are used to demonstrate how
galactic collisions could produce gravitational effects pulling enormous masses of gas
toward the center of the galaxies. The huge concentration could turn into a black hole,
". . .and matter swirling into the hole would generate prodigious amounts of radiation"
(Peterson 60). The extremely energetic, quasi-stellar object or quasar is thought to be
powered by supermassive black holes and the active galaxy is where these phenomena
reside.
These quasars and active galaxies that are billions of light-years away have been found
using radio astronomy and a technique called spectroscopy. Modern technological tools,
such as ground-based telescopes, space telescopes like Hubble, and the Very Long Baseline
Interferometry Space Observatory (VSOP), have also proven useful analytical tools for
astronomers. Black holes and quasars are interdependent theories. The explanation of
black holes leads to an explanation for quasars. These phenomena lead astronomers to
believe that there may be places in the universe where the laws of physics may break
down, opening doors to new theories for future astronomers (Hawkings).
Bibliography
Works Cited
Bartusiak, Marcia. "Outsmarting the Early Universe." Astronomy 26.10 (1998): 55-59.
Chaisson, Eric., and Steve McMillan. Astronomy Today. 3rd ed. Toronto: Prentice-Hall,
1999.
Disney, Michael. "A New Look at Quasars." Scientific American 278.6 (1998): 52-57.
Hawking, Stephen. "Universe." PBS Home Video. BBC-TV, 1997.
Olsen, Steve. "Black Hole Hunters." Astronomy 27.5 (1999): 48-55.
Peterson, Ivars. "The Birth of Twin Quasars." Science News 137.4 (1990): 60.
Voit, G. Mark. "The Rise and Fall of Quasars: Dormant Monsters May Lie Sleeping in Nearby

Galaxies." Sky & Telescope 97.5 (1999): 40-46.
Wiley, John P. Jr. "A Googolplex of Galaxies." Astronomy 27.5 (1999): 56-57.