Gas cloud in sight
Astronomers have discovered a pool of hot, ionized gas in our galaxy. It streams towards the extraordinarily dense object at the center of the Milky Way, then turns sharply around this object and finally shoots out the other side in a catapult-like manner. The gas is moving so fast that even the massive gravitational pull at the dense center of the galaxy (probably a black hole millions of times the mass of our Sun) cannot suck it up. Rather, it is propelled in a hyperbolic trajectory past the center by an annular cloud of cool molecular gas surrounding the center.
The findings are based on ten years of observations by a group led by Fahrrad Yusef-Zadeh, associate professor of physics and astronomy at Northwestern University. The scientists used the Very Large Array radio telescope in Socorro, New Mexico. Yusef-Zadeh presented the results at the American Astronomical Society Annual Meeting.
With optical telescopes, scientists cannot see through interstellar gas or interstellar dust in the Milky Way. So they rely on radio and infrared telescopes to study the galactic center, 25,000 light-years from Earth. The new results could give astronomers a new set of clues about the nature of the mysterious center that may really be a black hole.
"Basically, stars follow the force of gravity, with this ionized gas forming a coherent stream that responds not only to gravity, but also to other influences, such as stellar winds, tidal forces, and magnetic fields," said Yusef-Zadeh.
Together with other observations, the stream may help clarify the three-dimensional vortex picture at the center of the galaxy. Yusef-Zadeh discussed his findings with a German group of scientists who had imaged the moving stars near the center using an infrared camera, and with a group from Harvard University who had used radio telescope data to study the black hole's motion.
The gas stream, several thousand degrees hot, is in the form of a plasma. According to Yusef-Zadeh, the gas is zipping around the galactic center at over 3 million km/h within a fraction of a light-year.
"Something must have accelerated the gas to such a high speed. We just don't know what yet,” Zadeh remarked. One thing is clear: the gas won't stay there for long. It'll be here in a few thousand years."
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