Planck mass
In physics, the Planck mass, denoted by mP, is the unit of mass in the system of natural units known as Planck units. It is approximately 0.0217651 milligrams—about the mass of a flea egg. The Planck mass is the maximum allowed mass capable of holding a single elementary charge.
It is defined so that
where c is the speed of light in a vacuum, G is the gravitational constant, and ħ is the reduced Planck constant.
Particle physicists and cosmologists often use an alternative normalization with the reduced Planck mass, which is
The factor of simplifies a number of equations in general relativity.
The Planck mass is nature’s maximum allowed mass for point-masses (quanta) – in other words, a mass capable of holding a single elementary charge. If two quanta of the Planck mass or greater met, they could spontaneously form a black hole whose Schwarzschild radius equals their Compton wavelength. Once such a hole formed, other particles would fall in, and the black hole would experience runaway, explosive growth (assuming it did not evaporate via Hawking radiation). Nature’s stable point-mass particles, such as electrons and quarks, are many, many orders of magnitude lighter than the Planck mass and cannot form black holes in this manner. On the other hand, extended objects (as opposed to point-masses) can have any mass.
...
Wikipedia