Naked black-hole hearts live in the fifth dimension: Lehner has now proposed another situation where naked singularities might exist: in the extra dimensions proposed by string theory. The rub is that this time, they aren't unusual.
To understand why, think of black holes as points in the four dimensions we experience - three of space and one of time. These become "black strings" when extended into a fifth dimension of space (see diagram).
Black strings are unstable and break up into smaller black holes like a stream of water splitting into droplets. Lehner showed that at the point where a smaller black hole pinches off from the stream, the black hole's radius is zero, which means its density is infinite. In other words, it is a naked singularity. Lehner showed this will happen any time you have a black string.
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