WASHINGTON --- Astronomers have observed a swoosh of hot, ionized gas streaming toward the extremely dense object at the center of the Milky Way, bending sharply around it and slingshoting out the other side.
The speed of the ionized gas is so great that the tremendous gravitational pull of the dense galactic center, which is thought to be a black hole with a mass millions of times that of our sun, is unable to suck it in. Instead, it swings the ionized gas around it in a hyperbolic orbit and through a ring-shaped cloud of cool molecular gas that encircles the galactic center.
The findings represent 10 years of observations by a team led by Farhad Yusef-Zadeh, associate professor of physics and astronomy at Northwestern University, using the Very Large Array radio telescope in Socorro, N.M. He presented the results at the annual meeting of the American Astronomical Society.
Optical telescopes cannot see through the interstellar gas and dust within the disk-shaped galaxy, so scientists rely on radio telescopes and infrared telescopes to study the galactic center -- a maelstrom of awesome power that contains what Zadeh calls the galactic zoo of unusual and highly energetic phenomena -- 25,000 light years from Earth. The new finding adds yet another strange denizen to the zoo, but also may provide astronomers with a new set of clues to the nature of the mysterious black hole candidate.
"Stars basically follow the gravitational force, whereas this ionized gas follows a coherent flow that responds not only to gravitational pull but also to non-gravitational effects such as stellar winds, tidal forces and magnetic fields," Zadeh said.
Taken together with other observations, the flow may help clarify the three-dimensional picture of the whirlpool at the galactic center. Zadeh discussed his findings along with a German group that took infrared images of the motion of stars near the galactic center and a group from Harvard University that used radio telescope data to study the motion of the black hole.
Heated to more than ten thousand degrees, the gas stream exists as a plasma, its molecules stripped of their electrons to an ionized or electrically charged state. It hurtles around the galactic center at a closest distance of a fraction of a light year at more than two million miles per hour, Zadeh said.
"We dont know what its coming from, but something must have accelerated it to such high velocity," he said. "One thing thats obvious: this gas is not going to stick around for a long time. In a few thousand years, its outta here."
Zadeh's collaborators are Doug Roberts of the University of Illinois at Urbana-Champaign and John Biretta of the Space Telescope Science Institute in Baltimore.
EDITORS: FULL-COLOR FIGURE CAN BE VIEWED AND DOWNLOADED AT:
http://www.nwu.edu/univ-relations/media/Images/ionized_gas.JPG
Prints also available from Northwestern or at the meeting from Dr. Zadeh.
CAPTION FOR GRAPHIC:
Drawing of swirling gas at the center of the Milky Way. The hot, ionized streamer is shown as a smooth swoosh swinging past the black hole at the galactic center; cooler molecular gas is dotted. Blue regions are moving toward Earth, red regions are moving away from us.