The black hole X-ray transient XTE J1550-564 has undergone a strong outburst in 1998 and two relativistic X-ray jets have been detected years later with the \it Chandra X-ray observatory ; the eastern jet was found previously to have decelerated after its first detection .
Here we report a full analysis of the evolution of the western jet ; significant deceleration is also detected in the western side .
Our analysis indicates that there is a cavity outside the central source and the jets first traveled with constant velocity and then were slowed down by the interactions between the jets and the interstellar medium ( ISM ) .
The best fitted radius of the cavity is \sim 0.31 pc on the eastern side and \sim 0.44 pc on the western side , and the densities also show asymmetry , of \sim 0.034 cm ^ { -3 } on the east to \sim 0.12 cm ^ { -3 } on the west .
The best fitted magnetic fields on both sides are \sim 0.5 mG .
Similar analysis is also applied to another microquasar system , H 1743-322 , and a large scale low density region is also found .
Based on these results and the comparison with other microquasar systems , we suggest a generic scenario for microquasar jets , classifying the observed jets into three main categories , with different jet morphologies ( and sizes ) corresponding to different scales of vacuous environments surrounding them .
We also suggest that either continuous jets or accretion disk winds , or both may be responsible for creating these cavities .
Therefore X-ray jets from microquasars provide us with a promising method of probing the environment of accreting black holes .