NASA's WISE Takes a Bite Out of the Black Hole 'Doughnut' Theory

NASA's Wide-field Infrared Survey Explorer (WISE) surveyed more than 170,000 supermassive black holes, and their findings have taken a bite out of astronomers' long-held "doughnut" theory.

Active, supermassive black holes at the hearts of galaxies are characterized by how they feed on surrounding gas material that fuels their growth. They tend to fall into two categories: those that are hidden by dust, and those that are exposed.

The universally accepted theory is that every black hole is surrounded by a dusty, doughnut-shaped structure called a torus. Depending on how every one these "doughnuts" are oriented in space, the black holes will take on various appearances. For instance, if the doughnut is positioned so that we see it edge-on, the black hole is hidden from view, whereas if it's observed from above, below or face-on, the black hole is clearly visible.

However, the new WISE results do not support this theory.

Researchers measured the clustering of the galaxies containing both hidden and exposed black holes, or the degree to which the objects clump together across the sky.

After studying more than 170,000 active black holes, the findings suggest that something other than a doughnut structure may play a role in a black hole's appearance - though astronomers do not yet know what it may be.

"Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery," Lin Yan of NASA's Infrared Processing and Analysis Center, based at the California Institute of Technology in Pasadena, said in a statement. "We hope our work will inspire future studies to better understand these fascinating objects."

If the unified model were true, black holes obscured from view would cluster the same way exposed ones do. But the results showed the galaxies with hidden black holes are more clumped together than those of the exposed black holes, forcing scientists to rethink their previous theory.