  Double-lobed radio galaxies a few 100s of kpc in extent, like Cygnus A, are
common at redshifts of 1 to 2, arising from some 10 per cent of the most
powerful Active Galactic Nuclei (AGN). At higher redshifts they are rare, with
none larger than a few 10s of kpc known above redshift z~4. Recent studies of
the redshift evolution of powerful-jetted objects indicate that they may
constitute a larger fraction of the AGN population above redshift 2 than
appears from a simple consideration of detected GHz radio sources. The radio
band is misleading as the dramatic (1+z)^4 boost in the energy density of the
Cosmic Microwave Background (CMB) causes inverse Compton scattering to dominate
the energy losses of relativistic electrons in the extended lobes produced by
jets, making them strong X-ray, rather than radio, sources. Here we investigate
limits to X-ray lobes around two distant quasars, ULASJ112001.48+064124.3 at z
= 7.1 and SDSSJ1030+0524 at z=6.3, and find that powerful jets could be
operating yet be currently undetectable. Jets may be instrumental in the rapid
build-up of billion Msun black hole at a rate that violates the Eddington
limit.
