A black hole is an amazing phenomenon. It is invisible because it does not even allow light to escape. Nevertheless, it can be imaged. It concentrates mass in a very small part of space – so small that the conventional laws of physics lose their meaning. Nevertheless, physicists are getting closer and closer to its secrets. One of them is what a black hole looks like inside. Black, it is clear, is not there. Quite the opposite. Inside, all the mass and energy that cannot escape the event horizon are concentrated. If one could see in a black hole, one would have to notice a lot of brightness there.

Or not? In fact, the common idea is that a black hole is one thing above all: empty. All the mass is concentrated in its center, where it comes to the formation of a singularity, a hole in the space-time. But is this really so? The authors of a new study doubt it. They say: Black holes are in reality gigantic hairballs, as cats like to choke them out of their digestive organs. Well, that’s not exactly what the study says – the comparison is mine.

Actually, with their paper the authors try to end the debate about Stephen Hawking’s famous information paradox. It arose from Hawking’s conclusion that all data that enters a black hole can never leave it. This conclusion is consistent with the laws of thermodynamics, but contrary to the fundamental laws of quantum mechanics. “String theory has shown us that all the mass of a black hole is not sucked into the center,” said Samir Mathur, lead author of the study and a professor of physics at Ohio State University. “The black hole tries to squeeze things together up to a certain point, but then the particles get stretched out on these strings, and the strings start to stretch and expand, and you get a kind of ball of yarn that expands and fills the whole black hole.”

“The bigger the black hole is, the more energy is sucked into it, and the bigger the ball of yarn gets,” Mathur said. A 2004 study he authored found that string theory, could be the solution to Hawking’s paradox. With this hairball structure, the hole radiates like any normal body, and there is no mystery. But the inner structure of the hole changes. In recent years, therefore, other physicists have tried to reconcile Hawking’s conclusions with the old picture of the black hole, in which the black hole can be thought of as empty space with all its mass at the center. One theory, the wormhole paradigm, holds that black holes could be one end of a bridge in the space-time continuum, meaning that anything that enters a black hole could reappear at the other end of the bridge – the other end of the wormhole – at some other place in space and time. However, for the wormhole picture to work, some of the low-energy radiation would have to escape at the edges of the black hole.

Mathur and colleagues now show that black holes would not radiate as they do in this case. The researchers also examined physical properties of black holes, including topology changes in quantum gravity, to determine whether the wormhole paradigm would work. “In each of the versions proposed for the wormhole approach, we found that the physics was not consistent,” Mathur said. “The wormhole paradigm tries to argue that in some sense you can still think of the black hole as actually being empty when all the mass is in the center. And the theorems we prove show that such a picture of the hole is not possible.”

So if you ever crash into a black hole, you can expect that every single subatomic particle that makes you up will be distorted into a long string that, along with many others, will form the hairball that makes up the black hole. What happens if the universe chokes out this mass sometime (maybe from a white hole?) is left to your imagination.