The upper limit to the mass of a white dwarf (equals 1.4 times the mass of the sun).
theoretical limit below which a low-mass star can evolve into a white dwarf at the end of its life. Its value is 1.4 solar masses.
The theoretical upper limit at which a stellar remnant can form a white dwarf. Beyond this value (~1.4 solar masses) the electron degeneracy pressure is unable to withstand gravitational collapse and the electrons are forced into the nucleus where they combine with protons to form a dense sea of neutrons. The remnant star is then a neutron star.