  In general relativity all forms of energy contribute to gravity and not only
just ordinary matter as in Newtonian Physics. This fact can be seen in the
modified hydrostatic equilibrium equation for relativistic stars pervaded by
magnetic (B) fields. It has an additional term coupled to the matter part as
well as an anisotropic term which is purely of magnetic origin. That additional
term coming from the pressure changed by the radial component of the diagonal
electromagnetic field tensor, weakens the gravitational force when B is strong
enough and can even produce an unexpected change in the attractive nature of
the force by reversing its sign. In an extreme case, this new general
relativistic (GR) effect can even trigger an instability in the star as a
consequence of the sudden reversal of the hydrostatic pressure gradient. We
suggest here that this GR effect may be the possible central engine driving the
transient giant outbursts observed in Soft Gamma-ray Repeaters (SGRs). In small
regions of the neutron star (NS), strong magnetic condensation can take place.
Beyond a critical limit, these highly magnetised bubbles may explode releasing
the trapped energy as a burst of gamma-rays of ~ 10^{36-40} erg.
