Quasars And Active Galaxies

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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

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