''Fusor'' is a proposed term for an astronomical object which is capable of core fusion. The term is more inclusive than ''
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
''.
Motivation
To help clarify the nomenclature of
celestial bodies
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...
,
Gibor Basri proposed to the
IAU
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
that any "object that achieves core fusion during its lifetime" be called a fusor.
This definition includes any form of
nuclear fusion
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
, so the lowest possible mass of a fusor was set at roughly (
Jupiter masses) at which point
deuterium fusion becomes possible. This is significantly lower than the point at which sustained fusion of
protium (, "regular" hydrogen) becomes possible, around . Objects are considered "stellar" when they are about , when their
gravitational contraction is halted by the heat generated by core fusion, establishing
hydrostatic equilibrium
In fluid mechanics, hydrostatic equilibrium, also called hydrostatic balance and hydrostasy, is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. I ...
, and they become
main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
stars.
[ Fusors would include active ]star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s and many brown dwarf
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
s.
The introduction of the term "fusor" would allow for a simple definition:
* Fusor – An object capable of core fusion
* Planemo
A planetary-mass object (PMO), planemo, or planetary body (sometimes referred to as a world) is, by geophysical definition of celestial objects, any celestial object massive enough to achieve hydrostatic equilibrium, but not enough to sustain ...
– A round non-fusor
* Planet
A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
– A planemo that orbits a fusor
In this context, the word ''round'' is understood to mean "whose surface is very nearly on the gravitational equipotential", and ''orbits'' to mean "whose primary orbit is now, or was in the past around", and ''capable'' implies fusion is possible sometime during the existence of the object by itself.
See also
* Gas giant
A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...
* Mesoplanet
Mesoplanets are planetary-mass objects with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov. Assuming size is defined in relation to equatorial radius, mesoplanets should be approximately 500 km to 2,500 km ...
* Planetar (astronomy)
References
Star types
Definition of planet
{{stellar-astronomy-stub