  Repulsive gravity has its origin in the 1939 article of Oppenheimer and
Snyder which describes a collapsar, that is an idealized star of
non-interacting material (dust) collapsing under its own gravity. The stellar
material has a final state resembling a football, that is a significant part of
it is concentrated in a thin surface shell. An interior pressure is exerted by
the strong gravitational field, equivalent to a negative mass. However, the OS
solution has been misunderstood, the shell's position being incorrectly
identified with the "event horizon" in black-hole theory. While half the
material is concentrated in a shell occupying a small fraction of the radius,
some material is spread throughout the interior, unlike the concentration in a
black hole's singularity. We deal with the singularity in density at the shell
surface, by including Fermi pressure of degenerate electrons for a shell
density comparable to a solar mass-sized white dwarf. Because the high-density
region is concentrated in a shell, instead of at the centre as in a black hole,
our conclusion is that repulsive gravity enables the existence of supermassive
white dwarfs.
