Two types of stellar hazards can create higher-than-normal levels of ionizing radiation:
solar flares and
cosmic rays.
Solar flares release tremendous amounts of electromagnetic energy (including harmful ultraviolet rays and X-rays), as well as highly charged protons and electrons. The effects are comparable to a radioactive blast from one hundred million billion tons of TNT (compared to the 20,000-ton equivalent blasts that destroyed Hiroshima and Nagasaki). Fortunately, while
solar flares aren't rare, they are predictable.
An unprotected creature exposed to radiation from a
solar flare is treated as "severely irradiated" for the purposes of determining the radiation's effects (see Table: Radiation Exposure).
Cosmic rays, unlike
solar flares, cannot be predicted. Consisting of subatomic particles
moving at relativistic speeds, these rays can penetrate miles of solid mass (though extremely few get through the Earth's atmosphere without colliding with other atoms or molecules, effectively rendering them harmless). In space, these subatomic particles can cause severe cell
damage, even genetic
mutation.
An unprotected creature exposed to radiation from a
cosmic ray shower is treated as "highly irradiated" for the purposes of determining the radiation's effects (see Table: Radiation Exposure).