  The electromagnetic radiation by quark-gluon plasma in strong magnetic field
is calculated. The contributing processes are synchrotron radiation and
one--photon annihilation. It is shown that in relativistic heavy--ion
collisions at RHIC and LHC synchrotron radiation dominates over the
annihilation. Moreover, it constitutes a significant part of all photons
produced by the plasma at low transverse momenta; its magnitude depends on the
plasma temperature and the magnetic field strength. Electromagnetic radiation
in magnetic field is probably the missing piece that resolves a discrepancy
between the theoretical models and the experimental data. It is argued that
electromagnetic radiation increases with the magnetic field strength and plasma
temperature.
