What Is a Quasar?

Quasar is the term given to distant astronomical objects that emit tremendous amounts of energy. The term was originally derived as a shortening of the "quasi-stellar radio source" since little was known about them at the time other than the fact that they were powerful emitters of radio frequency energy. The energy output of quasars is exceeded only by the short outburst of a supernova or short duration gamma ray bursts. The quasar, however, is not a short duration astronomical event, but continues to output a steady stream of powerful radiation for millions or even billions of years. Although there are no quasars anywhere near our galaxy, it is now though to be quite likely that the Milky Way itself may have once been a quasar.

Telescopes are Time Machines

The wavelengths of light and other electromagnetic radiation that we detect from quasars is quite noticeably shifted toward red, which implies that quasars are speeding away from the Earth at very high velocities and are therefore among the most distant objects in our universe. Because of the great distance between us and all known quasars, it has taken billions of years for their light to reach our observatories, meaning that they represent objects that most likely no longer exist in the state in which we now observe them. In other words, what we see when we look at quasars are object from the distant past of our universe. Astronomers can literally see into the past.

What is a Galaxy?

To better understand quasars according to the most current scientific thoughts on the subject, we must first talk about the formation of galaxies. A galaxy is a collection of millions and millions of stars that are grouped together. Galaxies are often shaped like giant spiral pinwheels like our own Milky Way galaxy. The reason for this common characteristic is that in the center of each galaxy is an incredibly strong gravitational force that seeks to pull all the surrounding stars into it. As stars are pulled inward, they also preserve any existing angular momentum they had and much like the water swirling around the drain in a bathtub, the stars spiral around the galaxy's center of gravity giving it a pinwheel shape.

How Galaxies are Formed

But, we need to go back further in the life-cycle of a galaxy. Galaxies start out as vast accumulations of gases and dust. The gases are spread out over an area of space that is almost incomprehensibly large. Within this massive dust cloud, there are areas where the material is thicker and areas where there is less of it. Areas of higher dust concentrations develop their own gravitational pull and begin, over time, to pull more and more space dust into a smaller and smaller space. Eventually, these celestial dust balls become compacted under their own weight and as they continue to draw in more and more mass from the surrounding gas clouds, they eventually turn into stars. This happens over and over again throughout the massive dust cloud until it is full of stars.

The Creation of Black Holes in Young Galaxies

The entire accumulation also has a center of gravity that tends to try to pull the gas, dust, and even forming stars toward the center as well. So much matter gets pulled to the center that its gravitation force makes it collapse in on itself forming a black hole. Because the area surrounding this black hole is already densely packed with the inflowing gas and even the mass of entire stars, it grows quickly in astronomical terms. As matter is siphoned into the black hole it releases very large amounts of energy. With ordinary, mature galaxies, like the Milky Way, the rate at which material is drawn into the central black hole is greatly diminished since the thickest clouds and greatest bunching of forming stars have already fallen in or have been pushed away and only a relatively slow procession of distant material is being consumed in the galaxy's central black hole.

Self-Extinguishing Quasars

In a very young galaxy, however, the dust clouds are thick and there is a lot more matter in the region near the center. It is thought that this constant accretion of relatively high amounts of matter being ripped apart by extremely powerful gravitational forces of the central black hole that results in the extraordinary, and continuous release of radiation that we call a quasar. According to research by Steve Roy and Megan Watzke using data from NASA's Chandra X-ray Observatory, the energy of the quasar itself is now thought to create a kind of super solar wind that actually pushes away dust from itself and eventually decreases its own fuel supply until it can no longer sustain the energy output that is the principle characteristic of a quasar.

Summary: What is a Quasar?In short then, and leaving out a lot of more in-depth information, a quasar is young galaxy still full of thick dust and gas clouds near its central black hole. The constant accretion of these clouds and other stellar materials into that central black hole is the cause of the extremely high and sustained outpouring of radiation that we see with our radio telescopes and call quasars.

Sources:
NASA/Jet Propulsion Laboratory (2005, August 7). NASA's Spitzer Finds Hidden, Hungry Black Holes. ScienceDaily. Retrieved December 8, 2009, from http://www.sciencedaily.com­ /releases/2005/08/050805104705.htm

NASA. Quasars. Retrieved December 1, 2009 from http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level2/quasars.html

Steve Roy and Megan Watzke (2006, March 23). NASA's Chandra Finds Evidence for Quasar Ignition. Retrieved December 2nd from http://www.nasa.gov/centers/marshall/news/news/releases/2006/06-034.html