Bending a black hole can juice it up. In extra dimensions, a black hole behaves like a fluid and a solid at the same time, and flexing the solid form may generate an electric field.
Although these effects exist only in the theoretical realm, the underlying equations could help us puzzle out some of the real-world properties of the hot, superdense matter that existed right after the big bang.
In our four-dimensional universe – three of space and one of time – black holes occupy single points in space-time. String theory says that if you add a fifth dimension, the black hole becomes a black string. Adding a sixth yields a sheet, or a “black brane”.
This multidimensional universe has a boundary, which when described mathematically looks a lot like the equations for quark-gluon plasma, a primordial form of matter that can be created fleetingly in particle accelerators but which can be too chaotic to study directly. Effects at this boundary also apply to black brane behaviour, which means branes can be used to glean the properties of quark-gluon plasma.
But describing black branes requires Einstein’s equations, which are complex and unwieldy, says Joan Camps at the University of Cambridge, who was not involved in the new work. So one trick is to try to describe them as ordinary materials.
Previously, physicists showed that black branes follow the mathematics of fluid dynamics, which in turn allowed them to accurately predict the viscosity of quark-gluon plasma.
Now Jay Armas of Copenhagen University in Denmark and colleagues have shown that black branes can behave like solids as well. If the black brane has an electric charge, bending it converts mechanical stress into an electric field, as in piezoelectric materials. Armas hopes the results will yield further insights into quark-gluon plasma.
“This kind of black hole can be approximated by materials,” Camps says. “This is new progress, and it’s progress that you can formulate in terms of ordinary concepts.”