Black holes in magnetic monopoles

We study magnetically charged classical solutions of a spontaneously broken gauge theory interacting with gravity. We show that nonsingular monopole solutions exist only if the Higgs-field vacuum expectation value $v$ is less than or equal to a critical value ${v}_{\mathrm{cr}}$ which is of the order of the Planck mass. In the limiting case, the monopole becomes a black hole, with the region outside the horizon described by the critical Reissner-Nordstr\"om solution. For $v<{v}_{\mathrm{cr}}$ we find additional solutions which are singular at $r=0$ but which have this singularity hidden within a horizon. These have nontrivial matter fields outside the horizon, and may be interpreted as small black holes lying within a magnetic monopole. The nature of these solutions as a function of $v$ and of the total mass $M$and their relation to the Reissner-Nordstr\"o solutions are discussed.

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