Cosmic engine takes XMM-Newton by surprise
BY EMILY BALDWIN
ASTRONOMY NOW
Posted: April 15, 2008

ESA’s X-ray satellite, XMM-Newton, is taken by surprise by a rare type of galaxy, from which it has detected a higher number of X-rays than previously thought possible.

XMM-Newton has allowed astronomers to stare into the far reaches of the Universe at quasars, vast cosmic engines that pump energy into their surroundings. It is thought that an enormous black hole drives each quasar, and as matter spirals into the black hole, powerful radiation and magnetic fields present in the region eject some of the gas back into space. This outflow has a profound effect on its surrounding galaxy, creating turbulence in its gas and hampering star formation. Understanding the behaviour of quasars, therefore, is an important step to understanding the early history of galaxies.

Artist impression of a BAL quasar. Credit: ESA (Image by C. Carreau).

About 10-20% of all known quasars are termed BAL quasars, or ‘broad absorption line’ quasars, which harbor a thick cocoon of gas surrounding them. Most researchers believe that gas flows away from a BAL quasar along the equatorial direction of the accretion disc, with little X-ray emission, indicating that there is enough gas to absorb most of the X-rays given out from the region near the black hole. But according to the new research, some BAL quasars are behaving differently, spewing out material along their polar axes, at right angles to the accretion discs. Four of these misbehaving quasars were targeted again, and two of them were found to be emitting more X-rays than anticipated, indicating that there is no veil of absorbing gas surrounding these particular quasars, adding another twist to their evolutionary story.

“Perhaps there can be both equatorial outflows and polar outflows simultaneously from these objects,” says Junxian Wang of the University of Science and Technology, China, who lead the research. “But we need more data so that we can look into the details of the X-ray emission.” The research team plan to follow up this work by monitoring more BAL quasars over a longer period of time, but interim computer simulations suggest that the polar outflows, like the gas ejected from the accretion disc, are also material falling in, turned away by fierce radiation before it comes near the black hole. Only future observations, combined with computer modelling, will provide more answers to the formation and evolutionary processes of these giant cosmic engines.