  It is well-known that energy-momentum is the source of gravitational field.
For a long time, it is generally believed that only stars with huge masses can
generate strong gravitational field. Based on the unified theory of
gravitational interactions and electromagnetic interactions, a new mechanism of
the generation of gravitational field is studied. According to this mechanism,
in some special conditions, electromagnetic energy can be directly converted
into gravitational energy, and strong gravitational field can be generated
without massive stars. Gravity impulse found in experiments is generated by
this mechanism.
