  Electromagnetism appears to have the potential to alter the fate of
relativistic gravitational implosion. Coulomb forces, for example, can in
principle prevent the ultimate collapse of charged matter to a singularity.
Also, half a century ago, Mael Melvin noted that magnetic forcelines do not
collapse under their own gravity, no matter how strong the latter may be.
Instead, magnetic fields seemed capable of stabilising themselves against
gravitational self-contraction. Intrigued, Melvin wondered whether magnetism
could also support against the realistic collapse of charged matter. Here, we
look back into these issues by means of two complementary scenarios. The first
reconsiders Melvin's highly idealised "magnetic universe" and reaches the same
conclusion, namely that magnetic fields do not self-gravitate. The second is a
realistic collapse scenario, like that of magnetised massive compact stars.
Looking for answers to Melvin's question, we find that magnetic fields do show
a generic tendency to support against relativistic gravitational implosion. The
magnetic effect in question involves the curvature of the host space, it grows
stronger as the collapse progresses and the triggering agent is the field's
tension. In other words, the reason is the elasticity of the field lines and
their inherent tendency to react against anything that distorts them from
equilibrium. In this case, the distorting agent is the ever increasing
curvature of the collapsing host space.
