Particle creation leading to Hawking radiation is produced by the changing
gravitational field of the collapsing star. The two main initial conditions in
the far past placed on the quantum field from which particles arise, are the
Hartle Hawking vacuum and the Unruh vacuum. The former leads to a time
symmetric thermal bath of radiation, while the latter to a flux of radiation
coming out of the collapsing star. The energy of Hawking radiation in the
interior of the collapsing star is negative and equal in magnitude to its value
at future infinity. This work investigates the backreaction of Hawking
radiation on the interior of a gravitationally collapsing star, in a
Hartle-Hawking initial vacuum. It shows that due to the negative energy Hawking
radiation in the interior, the collapse of the star stops at a finite radius,
before the singularity and the event horizon of a black hole have a chance to
form. That is, the star bounces instead of collapsing to a black hole. A
trapped surface near the last stage of the star's collapse to its minimum size
may still exist temporarily. Its formation depends on the details of collapse.
Results for the case of Hawking flux of radiation with the Unruh initial state,
will be given in a companion paper II.Comment: 8 pg