the one moving away.
    It is not clear what causes the jet’s x-ray emission, thermal bremsstrahlung, or  inverse Compton emission, a phenomenon where rapidly moving electrons “share” energy with radio photons. The additional energy is enough to boost the radio photons to x-ray level. The greater sensitivity of new and improved x-ray observatories, such as AXAF, should be able to solve the puzzle of the jet’s x-ray emission.