A foe is a unit of
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...
equal to 10
44 joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force appli ...
s or 10
51 erg
The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...
s, used to express the large amount of energy released by a
supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...
. An acronym for "
power_of.html" ;"title="Exponentiation.html" ;"title="en to the Exponentiation">power of">Exponentiation.html" ;"title="en to the Exponentiation">power offifty-one ergs", the term was introduced by Gerald E. Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work".
[
]
Without mentioning the foe, Steven Weinberg proposed in 2006 "a new unit called the bethe" (B) with the same value, to "replace" it.
["Following the death of Hans Bethe last year, I have proposed a new unit called the bethe, where 1 B is 1051 ergs or 1044 J. This would replace the unit of 1051 ergs, which is commonly used by those studying supernovae – a field in which Bethe worked. Ian Mills, president of the consultative committee on units of the International Committee for Weights and Measures, has concurred and agreed that the bethe can be used." ]
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's current luminosity is the same as its average luminosity over its lifetime, it would release 3.827
W × 3.1536
s/
yr × 10
10 yr ≈ 1.2 foe. One
solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
has a
rest mass energy of 1787 foe.
See also
*
Orders of magnitude (energy)
This list compares various energies in joules (J), organized by order of magnitude.
Below 1 J
1 to 105 J
106 to 1011 J
1012 to 1017 J
1018 to 1023 J
Over 1023 J
}
, -
, 1050
,
, ≳1050 J
, Upper limit of 'apparent'/isotropic energy ...
References
Units of energy
Supernovae
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