Researchers Identify Black Holes of the Ocean

Huge eddies of water swirling in the ocean are the mathematical equivalent of black holes; they are so tightly shielded by their circular water path that nothing caught within them can escape.

Researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) and the University of Miami used satellite images to study some of the largest ocean eddies on Earth. At more than 90 miles (150 kilometers) in diameter, the eddies are so big that before now their boundaries have been undetectable.

But writing in the Journal of Fluid Mechanics, study authors George Haller, a professor of nonlinear dynamics at ETH Zurich, and Francisco Beron-Vera, a research professor of oceanography at the University of Miami, present their new mathematical technique for mapping the boundaries of the enormous eddies.

The biggest challenge in their research was finding what the authors call "coherent water islands" amid turbulent seas. Difficulty was increased by the whirlpooling motion the of the eddies, which makes them a chaotic environment where water is constantly churning.

Haller and Beron-Vera were able to effectively restore order to the chaos by isolating coherent water islands from a sequence of satellite observations.

Much to their surprise, the coherent eddies behaved like black holes. The researchers were able to observe a point around the eddies equivalent to a phenomenon called a photon sphere in a black hole. Photon spheres are created when light is far enough from the perimeter of the black hole that instead of being drawn down the black hole in a spiral, the light forms a circular orbit around the black hole itself.

Similar closed barriers around certain ocean eddies were identified by Haller and Beron-Vera.

"In these barriers, fluid particles move around in closed loops - similar to the path of light in a photon sphere. And as in a black hole, nothing can escape from the inside of these loops, not even water," the researchers wrote in a statement. "It is precisely these barriers that help to identify coherent ocean eddies in the vast amount of observational data available."

Several of the eddies the researchers identified in the Southern Ocean contained and transported the same body of water without leaking for an entire year.

Haller said the very fact that such coherent water orbits exist amidst complex ocean currents is surprising.

"Mathematicians have been trying to understand such peculiarly coherent vortices in turbulent flows for a very long time," said Haller.