The end of a black hole’s evolution may be a mind-bending kind of space-time independent of time. A new study proposes a method to tell how far any black hole is from reaching this end state.

Black holes are some of the weirdest things in the universe. They occur when mass is packed into a tiny volume, squished to its ultimate density.

Though observations suggest black holes are prevalent in the universe, scientists still don't really understand what goes on inside them. The equations of general relativity usually used to understand the physics of the universe break down in these cases.

"It is really beyond the physics we know," said Juan Antonio Valiente Kroon, a mathematician at Queen Mary, University of London. "To understand what happens inside a black hole, we need to invent new physics."

Mercifully, the physics for the end state of a black hole is somewhat simpler. A solution to the equations of general relativity was found that produced a situation called "Kerr spacetime." Scientists now think Kerr spacetime is what happens when a black hole has reached its final evolutionary state.

"Mainly the equations of relativity are so complex that for relativistic systems, the only way you can probe these equations is by means of computer," Valiente Kroon told "Solutions like this Kerr solution are really exceptional. The Kerr solution is one of the few explicitly known solutions to general relativity that have a direct physical meaning."