Čerenkov radiation

From Halopedia, the Halo wiki

Cherenkov radiation is a type of radiation emitted by plutonium, such as in HORNET mines, when transitioning from Slipspace to realspace[1]. It is extremely long-ranged, reaching across light-minutes.

It also seems that components of the MJOLNIR armor produces Cherenkov radiation, as the Recon Armor's design specifically reduced the amount of radiation emitted for stealth purposes[2].

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