A fusor is a term proposed to the IAU by Gibor Basri, Professor of Astronomy at the University of California, Berkeley, to help clarify the nomenclature of celestial bodies. Under his definition a fusor would be "an object that achieves core fusion during its lifetime." This definition included any form of nuclear fusion so the lowest possible mass of a fusor was set at roughly 13 times that of Jupiter, at which point deuterium fusion becomes possible. This is significantly smaller than the point at which sustained fusion of hydrogen becomes possible, around 60 times the mass of Jupiter. Objects aren't considered "stellar" until around 75 times the mass of Jupiter, when gravitational contraction, i.e., contraction of the object due to gravity, is halted by heat generated by the internal nuclear reaction.