Artist’s drawing of a black hole named Cygnus X-1, which formed when a large star caved in. This black hole pulls matter from the blue star beside it / NASA/CXC/M.Weiss

Despite its name, a black hole is not an empty void. Most black holes form when stars die in a supernova explosion, collapsing under their own gravity. When a star 10 times more massive than the sun dies in a supernova, for example, its mass can be squeezed into a ball with the diameter of New York City. The resulting gravitational field is so strong not even light can escape.

For decades, astrophysicists have wondered whether black holes destroy information -- meaning what falls into them is lost forever. A new model suggests that at the end of their lives, black holes turn into “white holes,” explosively pouring all the material they have ever swallowed into space, Nature reports.

According to the new model, developed by Carlo Rovelli and Hal Haggard from Aix-Marseille University in France, the transformation from a black hole to a white hole would occur right after the initial formation of the black hole. Their model is based on a theory called “loop quantum gravity” -- where gravity and space-time are quantized, woven from tiny-individual loops that can’t be subdivided any further.

As a dying star collapses under its own gravity, it’s surrounded by a boundary called the event horizon: the point of no return, past which nothing can escape the black hole’s gravity. The star will continue to shrink, but eventually it will reach a stage where it can’t get any smaller because the loops cannot compress anymore.

At this point, the loops exert an outward pressure called “quantum bounce,” which transforms the black hole into a white hole. According to the team’s rough estimates, it takes just a few thousandths of a second for a black hole to transform into a white hole. Yet even though the transformation is nearly instantaneous, the researchers say, black holes can still appear to us as lasting billions or trillions of years because their gravity stretches light waves and dilates time.

If that’s the case, then rather than being shrouded by a true, eternal event horizon, black holes would be concealed by a temporary “apparent horizon,” Rovelli says. That’s important, because a true event horizon might violate the laws of physics.

In the 1970s, Stephen Hawking of the University of Cambridge calculated that a black hole should emit radiation out of its event horizon, slowly losing energy and shrinking in the process until it completely disappears. But that means information carried by matter falling into black holes would vanish forever. “There is no escape from a black hole in classical theory," the famed physicist told Nature earlier this year, "but quantum theory enables energy and information to escape.”

Having black holes turn into white holes could solve one of fundamental physics’ most troublesome questions. Their work is available at arXiv.

[Via Nature]