  Gravitation, the universal attractive force, acts upon all matter (and
radiation) relentlessly. Left to itself, gravity would pull everything together
and the Universe would be nothing but a gigantic black hole. Nature throws
almost every bit of physics - rotation, magnetic field, heat, quantum effects
and so on, at gravity to escape such a fate. In this series of articles we
shall explore systems where the eternal pull of gravity has been held off by
one or another such means.
