Čerenkov radiation

Čerenkov radiation (also spelled Cerenkov or Cherenkov) is electromagnetic radiation emitted when a charged particle (such as a proton) passes through an insulator at a speed greater than the speed of light in that medium. The characteristic "blue glow" of nuclear reactors is due to Čerenkov radiation. It is named after Russian scientist Pavel Alekseyevich Čherenkov, the 1958 Nobel Prize winner who was the first to characterize it rigorously.

During transitions from Slipspace to normal space, or vice versa, the glow of Cherenkov radiation emitted by a ships fissile materials, such as plutonium, can give its presence away to enemy forces. It also seems that components of the MJOLNIR armor produce Cherenkov radiation, as the Mark VI MJOLNIR Powered Assault Armor/R variant's design specifically reduced the amount of radiation emitted for stealth purposes.

Contradictions
Cherenkov radiation only occurs in a medium such as air or water because the speed of light in the medium is slowed. An electron cannot go faster the the speed of light in a vacuum, so this phenomena cannot happen in space as mentioned in the book Halo: Ghosts Of Onyx.