NASA's Chandra X-ray Observatory has tracked for the first t

by Steve Roy of Marshall Space Flight Center

A series of images from NASA's Chandra X-ray Observatory has tracked for the first time the life cycle of large-scale X-ray jets produced by a black hole. As the jets evolved they were observed to travel at near light speed for several years before slowing down and fading.

"Watching these jets slow down and disappear is like watching a time-lapse movie of the rise and fall of the Bronze Age," said Stephane Corbel of the University of Paris, lead author of a Science magazine paper describing the results. "Since they came from a stellar black hole in our galaxy, we have been able in a few years to watch developments that would take thousands of years to occur around a supermassive black hole."

Astronomers have been using Chandra and radio telescopes to observe two opposing jets of high-energy particles emitted following an outburst detected by NASA's Rossi X-ray Timing Explorer in1998 from XTE J1550-565, a double star system. The X-ray jets, which require a continuous source of trillion-volt electrons to remain bright, have been moving at about half the speed of light. Four years later they are more than 3 light years apart and slowing down. One of the jets has recently been observed to fade.

"The ejection of jets from stellar and supermassive black holes is a common occurrence in the universe, so it is extremely important to understand the process," said John Tomsick of the University of California, San Diego the lead author of an Astrophysical Journal paper describing the research. "For the first time, we have observed a jet from the initial explosion until it faded."

The observations indicate that one jet, the eastern jet, is moving along a line tilted toward Earth whereas the western jet is tilted away from Earth. This alignment explains why the eastern jet appears to have traveled farther than the western one. However, with this alignment, the eastern jet should be brighter than the western one, while during 2002 the western jet was actually three times brighter.

"This poses a puzzle. The simple model for jets doesn't explain what we are seeing," said Phil Kaaret of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author of another upcoming Astrophysical Journal paper on XTE J1550. "Either the black hole may somehow be feeding more energy into the western jet, or that jet has run into a dense cloud.

As jets plow through the interstellar gas, the resistance of the gas slows them down like air resistance slows down moving objects on Earth. Although all jets are assumed to decelerate in this way, the observations of XTE J1550-564 mark the first time jets have been caught in the act of slowing down. The observed deceleration underscores the value of black holes in our galaxy for studying similar processes that occur in quasars and active galactic nuclei.

XTE J1550-564, which is about 17,000 light years from Earth, was observed with Chandra's Advanced CCD Imaging Spectrometer and the High Energy Transmission Grating instruments. Radio data used in this study were obtained by the Australia Telescope Compact Array.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.