Technology Review: physics arXiv blog: 2010 March 15

String theory implies that black holes can come in all kinds of forms and flavours, according to a cosmologist who has catalogued all known types.

String theory is physicists' best guess at a unified theory of all interactions but it comes with some strange predictions. One of these is that spacetime consists of ten dimensions rather than just the four we're familiar with. And that raises some interesting questions.

One of them is what shape singularities can form in this higher dimensional space. In four dimensions, the only solution is spherical and that's the type of black holes cosmologists have imagined all over the universe.

But in higher dimensions, there are all kinds of other solutions. We've looked at the possibility of black rings but today Maria Rodriguez at the Max Planck Institute for Gravitational Physics in Golm, Germany, compiles a catalogue of all know species of black hole.

It turns out there's a whole managerie of other black hole solutions. Here are just a few: the black saturn, the black helical ring, the di-ring, the black bowtie and the bicycling black ring as well as the more general blackfolds.

While these solutions may exist mathematically, they may or may not exist in the real Universe. In fact, Rodriguez is able to work out certain criteria that a solution must meet for it to have a hope of existing in the real world. For example, a black ring can only exist if there is enough centrifugal repulsion to prevent it from collapsing.

*On the black hole species (by means of natural selection)*arXiv.org > hep-th > arXiv:1003.2411v1 > 2010 March 11

Maria J. Rodriguez wrote:Recently our understanding of black holes in D-spacetime dimensions, as solutions of the Einstein equation, has advanced greatly. Besides the well established spherical black hole we have now explicitly found other species of topologies of the event horizons. Whether in asymptotically flat, anti-deSitter or deSitter spaces, the different species are really non-unique when D > 4. An example of this are the black rings. Another issue in higher dimensions that is not fully understood is the struggle for existence of regular black hole solutions. However, we managed to observe a selection rule for regular solutions of thin black rings: they have to be balanced i.e. in vacuum, a neutral asymptotically flat black ring incorporates a balance between the centrifugal repulsion and the tension. The equilibrium condition seems to be equivalent to the condition to guarantee regularity on the geometry of the black ring solution. We will review the tree of species of black holes and present new results on exotic black holes with charges.