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Black hole outburst looks 'faster than light'
By Richard Stenger (CNN)
(CNN) -- Resembling cannon shots from a ship at night, one toward shore and the other away, two X-ray jets streaming from a black hole have been observed during their entire trajectories for the first time. The milestone, accomplished with one of the most powerful space telescopes, could help explain the behavior of a variety of mysterious objects that populate the universe. The Chandra X-ray Observatory captured the evolution of the cosmic jets, which spurt from everything from dense stars to black holes to active galactic cores. "For the first time, we have observed a jet from the initial explosion until it slowed and faded," said John Tomsick of the University of California, San Diego, one of several scientists who announced the findings Thursday. "The ejection of jets from stellar supermassive black holes is a common occurrence in the universe, so it is extremely important to understand the process," he said. The jets seemed to start out faster than the speed of light, then slow down as they collided with interstellar gas and dust, much as air resistance decreases the speed of objects moving through the atmosphere. "Initially the jets have been launched at a velocity close to the speed of light. Due to an optical illusion, the jet pointed toward us appeared to move faster than the speed of light," University of Paris astronomer Stephane Corbel said. "Then the jets propagate into the interstellar medium and gradually slow down to velocities slower than the speed of light," said Corbel, lead author of a report on the matter in this week's journal Science.
In the Chandra images, the outbursts brighten when they run into clouds of gas and dust, their kinetic energy converting into X-ray radiation. They then fade as the interstellar medium slows then to a crawl. The initial burst was spotted by another NASA X-ray space telescope in 1998. Four years later, the jets are more than three light-years apart. They came from a binary or double star system known as XTE J1550-564. Astronomers think that the system consists of a black hole that siphons gas from a companion star, which fuels the X-ray jets. XTE J1550-564 is about 17,000 light-years away in the constellation Norma. While complete, the jet show has confounded astronomers. In the images, the jet on the right is the one heading away from our direction. Due to the perspective, it should be dimmer than the one on the left. Yet the opposite is true. "This poses a puzzle. The simple model for jets doesn't explain what we are seeing. Either the black hole may somehow be feeding more energy into the western [right] jet or that jet has run into a dense cloud," said team scientist Phil Kaaret of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The center manages the Chandra space telescope for NASA, which unveiled the new images Thursday at the space agency headquarters in Washington, DC.
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