  We have discovered at x-ray and radio wavelengths large-scale moving jets
from the microquasar XTE J1550-654. Plasma ejected from near the black hole
traveled at relativistic velocities for at least four years. We present direct
evidence for gradual deceleration in a relativistic jet. The broadband spectrum
of the jets is consistent with synchrotron emission from high energy (up to 10
TeV) particles accelerated in shock waves formed within the relativistic ejecta
or by the interaction of the jets with the interstellar medium. XTE J1550-654
offers a unique opportunity to study the dynamical evolution of relativistic
jets on time scales inaccessible for active galactic nuclei jets, with
implications for our understanding of relativistic jets from Galactic x-ray
binaries and active galactic nuclei.
