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.