Presence of a massive black hole can be also determined by something other than a dusty 'doughnut' which is also called a torus, NASA researchers claimed.

The ten-year-old "doughnut theory" states that black holes are similar but they are surrounded by a doughnut-shaped dusty structure called Torus. Dependent on the course of the doughnut in space in relation to the black hole and course of observation, black holes' appearance differs.

To put the ten-year-old theory to test, the researchers observed as many as 170,000 supermassive black holes using NASA's Wide-field Infrared Survey Explore (WISE).

They, they measured the grouping of the galaxies that consist hidden as well as visible black holes. They found that the galaxies containing hidden black holes were more clustered together than those that that contained visible black holes.

The researchers also concluded that a black hole's presence could also be determined by something other than a Torus, at least in some circumstances. But, the details remained a mystery.

Lin Yan, from NASA's Infrared Processing & Analysis Center, said, "Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery." He added that the new findings showed that the doughnut theory doesn't provide all the answers.

The detailed research published in the most recent edition of Astrophysical Journal.