  The frozen star is a non-singular, ultracompact object that, to an external
observer, looks exactly like a Schwarzschild black hole, but with a different
interior geometry and matter composition. The frozen star needs to be sourced
by an extremely anisotropic fluid, for which the sum of the radial pressure and
energy density is either vanishing or perturbatively small. Here, we show that
this matter can be identified with the string fluid resulting from the decay of
an unstable $D$-brane or a brane-antibrane system at the end of open-string
tachyon condensation. The string fluid corresponds to flux tubes emanating from
the center and ending at the Schwarzschild radius of the star. The effective
Lagrangian for this fluid can be recast into a Born-Infeld form. When the fluid
Lagrangian is coupled to that of Einstein's Gravity, the static, spherically
symmetric solutions of the equations of motion are shown to be the same as
those describing the frozen star model. Frozen stars can therefore be viewed as
gravitationally back-reacted BIons. The Born-Infeld Lagrangian provides a
complete set of equations that describe the dynamics of the frozen star in a
generic state, which is not necessarily static nor spherically symmetric.
Additionally, this description provides a new physical perspective on the
structure of the frozen star in terms of the corresponding electric fields and
charges. The electric field is sourced by a point-like charge at the center of
the star, while its outer layer is equal and oppositely charged. The electric
force between the charges is offset because the mass of the star is fixed.
