Black strings: Black holes with extra dimensions
If black holes sound ominous, look out for their big, bad cousins: black strings. These are the five-dimensional analogues of black holes that might exist if our universe has hidden extra dimensions.
Thu, Sep 23, 2010 at 01:33 PM
BEYOND 3-D: Five-dimensional black strings evolve into black holes connected by black string filaments, in this computer simulation. (Photo: Pretorius/Lehner)
Meet the bizarro universe version of a black hole: a black string.
These hypothetical objects might form if our universe has hidden extra dimensions beyond the three of space and one of time that we can see, scientists say. A new study of five-dimensional black strings offers a glimpse into how these strange objects might evolve over time — if indeed they exist at all.
While it's difficult to visualize a five-dimensional object in our three-dimensional space, black strings would be cylindrical, researchers said. Think of a three-dimensional spherical black hole that's copied and stacked out in one direction to create an oblong shape.
"One of the problems that comes with thinking about higher dimensions is it's hard to even picture these things," said researcher Luis Lehner of the Perimeter Institute for Theoretical Physics, the University of Guelph and the Canadian Institute for Advanced Research, all in Canada.
Like black holes, black strings would be created when matter is squished so dense that the curvature of space-time becomes so large that even light cannot escape.
Lehner and colleague Frans Pretorius of Princeton University in New Jersey used a computer simulation to study how black strings would behave. Their results are detailed in a recent issue of the journal Physical Review Letters.
Holes and strings
The simulations reveal that a black string probably wouldn't be stable for long. Any small perturbation or deformation of its shape would set off a cascading pattern. [Animation of a black string]
Say, for example, the cylinder was squeezed slightly in its center, giving it the shape of an hourglass. Gravity would then tug at the neck, causing it to stretch out until the object becomes a set of spherical black holes connected by a filament of black string. Then, on the string segment, smaller black holes would likely form like beads on a wire, in a process that would go on repeating.
While the simulations would have required too much computer power to trace this process too long, the researchers say they can guess what the end point might be from the three generations they were able to observe. For certain models, small perturbations to the extra dimensions would probably cause all the black holes and strings to ultimately merge into one giant black hole.
While the idea of extra dimensions may sound wacky, physical theories suggest it's a distinct possibility. Just how many hidden dimensions exist depends on the theory, but some versions of the popular string theory, for example, postulate we live in a 10- or 11-dimensional universe.
"If there are extra dimensions they might be very, very small – little curled up dimensions" that would not be visible in our macroscopic three-dimensional space, Pretorius told LiveScience.
If this is the case, we may not be able to recognize the hidden dimensions in everything, including black holes.
"The things we know of as black holes might really be black strings but we can't see the other dimensions," Pretorius explained.
And black holes aren't the only possible black objects that could exist in higher-dimensions. Another hypothetical black object is a black Saturn, which would look like a spherical black hole surrounded by a donut-shaped torus. Or there might be black rings, which would simply be ring-shaped.
"Strings versus rings depends largely on the type of extra dimensions you have," Pretorius said.