The Brightest Objects With the Darkest Hearts

from Lake Afton Public Observatory

Few celestial objects have fueled as much controversy or changed the course of astronomical thought as have the enigmatic "little monsters" known as quasars. In a space not much larger than our solar system (which in astronomical terms is just a speck of dust), rages an inferno so powerful as to outshine a trillion suns. What could possibly cause such a tremendous outburst? Where can you find one?

The Discovery of Quasars

In 1962, British astronomer Cyril Hazard discovered an anomalous radio source using an ingenious method of increasing the resolution of existing radio telescopes by employing the moon as a marker. When the moon would pass in front of the radio source (called an occultation) the precise instant the radio signal stopped and then reemerged on the other side of the moon was carefully noted. This allowed the position of the radio source to be pinpointed to a very high degree of accuracy. It turned out that this radio source, then known only as 3C273, could be traced to a single starlike object in the constellation of Virgo. This object, although looking much like an ordinary star, was very peculiar. First, it was emitting a tremendous quantity of radio signals which would vary rapidly, indicating that the object must be relatively small. Secondly, the optical analysis of the object showed a spectrum unlike anything previously encountered. Thus the term Quasar was born. Quasar is derived from the words quasi- stellar radio source, meaning "starlike radio source".

On February 5, 1963, Maarten Schmidt, in a brilliant flash of insight, deciphered the strange spectrum observed. He realized he was looking at normal spectral lines for hydrogen, only the lines were Doppler-shifted so far toward the red end of the visible spectrum as to make them almost unrecognizable. This is the same basic phenomenon as listening to a train receding from you: the pitch of the sound appears to go down toward the low end of the sound spectrum. There was only one possible explanation--this object was receding away from us at almost 30,000 miles (48,000 kilometers) per second! From the accepted picture of the expansion of the Universe, called Hubble's Law, this placed the object at a distance of 3 billion light years. (A light year is the distance that light travels in one year, or about 6 trillion miles (9+ trillion kilometers).)

What is a Quasar?

Simply put, astronomers do not yet know what a quasar is, but they have developed very successful models that can explain many of the observed characteristics.

The first characteristic of a quasar is that the signal from them should vary with periods of perhaps a few hours to a few days. This means that the object itself must be about the size of our solar system. Something cannot vary its signal faster than the signal can travel across it. Since the signal being sent is light, the object must be from a few light hours (the distance light takes to travel in a few hours) to a few light days (the distance light takes to travel a few days) in size.

The second major characteristic is that these relatively small objects emit an incredible amount of light and energy--from around 100 billion to 10 trillion times that of the Sun . The only known culprit for such an outpouring of energy, according to present understanding, could be a very massive, rotating black hole. This black hole would need to have a mass of about 100 million times that of the Sun. Such a massive object would exert such an incredible gravitational influence on anything in its vicinity that it would literally rip everything apart. The "captured" material would then spiral toward the black hole, accelerating and heating to millions of degrees. About 10% or more of its mass would be converted to pure energy, according to the equation E = mc2. The spiraling material would form what is called an accretion disk, or plane of orbiting material, that would not only be super-heated but also charged or ionized. The temperature and charge of the material explain all the types of radiation observed from a quasar.

Where Can You Find a Quasar?

The last characteristic is that of a quasar's so- called "red shift". According to Hubble's Law, the entire universe is expanding. The velocity of the expanding material is proportional to the distance from us. The farther away something is, the faster it is flying away from us. Quasars' characteristic red shift indicate distances of billions of light years. This means that they are the most distant observable objects. It also means that the light that is reaching us from these most distant of objects is billions of years old. For all we know, objects such as quasars do not really exist today. They may be the early stages in the formation of galaxies.

Exploring the Frontier

Quasars give astronomers some of the most challenging and interesting questions yet posed by the mysterious universe in which we live. It is because of the incredible distance to these objects that the evolution and size of the universe can be estimated. Better understanding these "enigmatic little monsters" will require a much closer look at the fringe of our universe with more precise and sophisticated equipment than is available today. But our vision of the edge of the universe, and therefore the most distant past, is improving day by day.

References and Articles

Astronomy Magazine, December 1991.

Time-Life Books, Voyage Through the Universe, "Galaxies".

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