Quasars Confound With X-rays

Author:  Jessica Kloss

Institution:  Princeton University
Date:  May 2008

A recent look into the some of the farthest reaches of the universe has revealed that certain Quasi-Stellar Objects , which are more commonly known as "quasars" , emit more X-rays than researchers previously thought possible, showing that current theories about these mysterious objects still need some work. This discovery, described in a paper published March 20th by JunXian Wang and his team of researchers at the University of Science and Technology of China , Hefei, may help get us one step closer in understanding the inner workings of some of the strangest objects in the universe.

Quasars are like cosmic engines, pumping vast amounts of radiation into space. Researchers widely believe that each quasar is powered by a black hole. According to current computer simulations, the shape of a quasar is roughly like that of a wheel on an axle , the black hole is in the center of the wheel, and the "accretion disc," or the matter swirling into the black hole like water down the bathtub drain, is the wheel.

The friction of the material swirling into the black hole makes the accretion disc heat up and give off powerful radiation. The radiation then causes the quasar to eject into space some of the material falling into the black hole perpendicular to the accretion disc , in other words, this ejected material looks like an axle to the "wheel" of the accretion disc.

Based on information from the satellite XMM Newton, which was specially designed to pick up X-rays outside the interference from the Earth's atmosphere, Wang and his team determined that from a certain angle, a type of quasar called a "broad emission line" quasar (BAL quasar) seemed to give off the same amount of X-rays as normal quasars. This result is unexpected because in general these quasars are characterized by giving off less X-rays than normal quasars, leading researchers to believe, based on computer simulations, that BAL quasars have a cloud of gas around them that absorbs most of the X-rays. Now, Wang said, "Our results can help refine the computer simulations of how these quasars work."

Wang's study included only BAL quasars that were facing us straight on, that is, with the ejected material pointing towards Earth, which limits the number of quasars used. Further, BAL quasars are also relatively rare, making up only one or two out of ten quasars. Because of these factors, the satellite study included only four quasars. While even this small sample showed that the expected cloud of gas must not have been present, more information will help researchers to make better models. As Wang says, "We need more data so that we can look into the details of the X-ray emission," and thereby learn more about these cosmic engines.

Written by Jessica Kloss

Reviewed by Jeff Kost, Pooja Ghatalia

Published by Pooja Ghatalia