For the first time, astronomers have tracked the life
cycle of X-ray jets from a black hole. A series of images
from NASA’s Chandra X-ray Observatory revealed the jets
traveled 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 VII and the
French Atomic Energy Commission in Saclay, lead author of the
paper in the Oct. 4 issue of the journal Science. “Since the
jets came from a stellar black hole in our galaxy, we
watched, in only a few years, developments that would have
taken thousands of years to occur around a supermassive black
hole in a distant galaxy,” he said.
Astronomers have been using Chandra and radio telescopes to
observe two opposing jets of high-energy particles emitted
following an outburst, first detected in 1998 by NASA’s Rossi
X-ray Timing Explorer, from the double-star system XTE J1550-
564. The X-ray jets, which require a continuous source of
trillion-volt electrons to remain bright, were observed
moving at about half the speed of light (approximately 93,000
miles per second). Four years later, they are more than three
light-years apart, slowing down and fading.
“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. He is
the author of an Astrophysical Journal paper scheduled for
January 2003 publication describing the research. “For the
first time, we have observed a jet from the initial explosion
until it slowed and faded,” he said.
The observations indicate that one jet, the eastern jet, is
moving along a line tilted toward the Earth, whereas the
western jet is pointed away from the Earth. This alignment
explains why the eastern jet appears to have traveled farther
from the black hole than the western one. However, with this
alignment, the eastern jet should be brighter than the
western one, while 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 J1550-564. “Either the black hole may somehow be
feeding more energy into the western jet, or that jet has run
into a dense cloud,” he said.
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 believed 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 small, stellar black holes in our galaxy for studying
similar processes that occur in distant 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 for the Office of Space Science,
Washington, 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.
Images and additional information about this result are
available at:
