A foe is a unit of energy equal to 1044 joules or 1051 ergs, used to measure the large amount of energy produced by a supernova.[1]
The word is an acronym derived from the phrase [ten to the power of] fifty-one ergs.[2] It was coined by Gerald Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work".[3]
This unit of measure is convenient because a supernova typically releases about one foe of observable energy in a very short period (which can be measured in seconds). In comparison, if the Sun had its current luminosity throughout its entire lifetime, it would produce 3.827×1026 W × 3.1536×107 s/yr × 1010 yr ≈ 1.2 foe.