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Quasars vs. Stars: What are the Differences?

written by: Reeja Mathew•edited by: RC Davison•updated: 5/23/2010

Quasars are a relatively new member to the zoo of cosmic objects astronomers study, having been first discovered in the 1950's. Many questions are still unanswered about quasars and sometimes they are confused with stars. This article discusses the difference between stars and quasars.

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    Quasars And Stars : What are They ?

    Quasars and stars are two very different groups of celestial objects. Scientists differ in their opinion about exactly what quasars are. Quasars are star like point sources with immense energy and much greater red shifts, whereas the stars are self illuminating celestial objects with energy outputs much less than that of quasars.

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    Difference in Evolution

    Stars in Milky Way 

    Life of Stars:

    The primordial matter generated from the big bang resulted in the formation of hydrogen rich clouds, which collapsed under their own gravitational pull. This process continued until the temperature and pressure inside the core of the clouds become high enough to start a nuclear fusion reaction, and thus stars were born. The hydrogen will fuse into helium, the process continues until the star runs out of the hydrogen and then it will begin burning the helium. Eventually the star will bloat to red giant stage. Depending upon its initial size it will eventually become a white dwarf ,and finally cool to a black dwarf, or become a supernova, which finally ends up either as a neutron star or a black hole. The image above shows a star cluster which resides outside of the Milky Way galaxy.

    A Gamma Ray Quasar 

    Life of Quasars:

    Based on the studies conducted, scientists now believe that quasars are nuclei of distant active galaxies. Many of the galaxies are believed to have a central massive black hole, which attracts matter into it. This matter forms an accretion disk around these black holes. Due to frictional heating from collisions these particles have as they rotate about the black hole, they will reach extremely high temperatures. so high that the nuclei of these galaxies out-shine all of the rest of the stars in that galaxy. Besides that, as the matter is devoured by these black holes, enormous amount of energy will be released by the matter falling into the black hole, which then radiates as cosmic jets along the south and north poles of these black holes.

    An alternative theory is that quasars are actually part of some new type of galaxy. As we are not completely aware of the processes which occur during the formation of a galaxy, some scientists believe that these quasars may be the initial stage of galaxy formation. In 1959 the first quasar was detected, which is named – 3C 273, in the constellation Virgo. In 1963, T. Matthews and A. Sandage detected a large redshift in the spectrum of 3C 273, indicating that the object was possibly a distant galaxy. The image above shows a quasar.

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    Difference in Luminosity

    Basically stars are self illuminating bodies, which create energy through nuclear fusion reactions. But even the most studied star that is our Sun, has a very low luminosity compared with the quasars. Quasars, or quasi-stellar radio sources are point sources, which are visible because of the material they pull in. Quasars may have the highest luminosity among all objects in the universe, which makes them visible through telescopes even though they are at extremely large distances from the Earth. The average luminosity of the Sun is 3.839 x 1026 W whereas the luminosity of a bright quasar is around 10 42 W.

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    Difference in Shift in Spectral Lines

    The spectrum obtained from the quasars indicate very high values of red shift, which points to that fact that not only are they very far from us, but they are moving away from us at a very fast pace. They are the biggest known sources of energy among cosmic objects. Most of these quasars are billions of light years away from us. So the light took billions of years to reach the Earth, which means that what we are observing is a light from an ancient object. Whereas the stars in our galaxy are very close compared to the distance of quasars. Unlike quasars, the shift in spectral lines is different among stars in that is some show blue shift (they are moving toward us) whereas some others show red shift.

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    Quasars have a size comparable with that of our solar system. But scientists still find it difficult to explain the source of such an enormous amount of energy. Differences between stars and quasars are only a few, but there may arise more when the mysteries surrounding quasars are fully resolved.