Astronomers are rethinking assumptions about black holes, after new evidence punctured holes in the so-called "doughnut" theory of their appearance. So far, scientists had believed the unified theory of active, supermassive black holes sufficiently explained why they could vary widely in how they looked, but results from NASA's Wide-field Infrared Survey Explorer (WISE) have thrown that into disarray.
The unified theory argued for several decades that active black holes are surrounded by a "doughnut" of dust in a torus shape. The way the black hole itself appears depends on the angle at which it's seen, and so how much of that torus is in the way.
Viewed face-on, and the black hole would be clear, the theory's authors suggested. From the side, however, the dust would occlude the black hole.
However, having examined more than 170,000 active massive black holes, a team using WISE data has thrown doubt onto the unified theory.
Lin Yan of NASA's Infrared Processing and Analysis Center (IPAC), based at the California Institute of Technology in Pasadena, Emilio Donoso, now of the Instituto de Ciencias Astronómicas, de la Tierra y del Espacio in Argentina, Daniel Stern at NASA's Jet Propulsion Laboratory in Pasadena, California, and Roberto Assef of Universidad Diego Portales in Chile and formerly of JPL, came up with results that do not match what the existing explanation would predict.
Calculating clustering of hidden and exposed black holes, which should follow the same patterns under the unified model, the team found that hidden examples were actually far denser than those exposed.
Unfortunately, there's no actual explanation for why that's the case, though the astronomers have several leads they're following. One relates to dark matter, bigger halos of which coincide with hidden black holes.
Further investigation of the WISE data is underway, but the assumption is that the unified theory went too far in trying to make the appearance of black holes simplistic. Scientists may now have to backtrack from that and accept more granular differentiation.