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For Fully Mature Black Holes, Time Stands Still

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 SPACE.com. "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."

Kerr spacetime is time-independent, meaning that nothing in Kerr spacetime

changes over time. In effect, time stands still. A black hole in such a state

is essentially stationary.

"One could say once it has reached this stage, there are no further processes

taking place," Valiente Kroon said.

In their new study, Valiente Kroon and Thomas Backdahl, his colleague at Queen

Mary, have calculated a formula to determine how close a black hole is to

reaching the Kerr state.

This can happen very quickly even in seconds depending on the object's

mass.

To apply the formula, scientists would examine the region around a black hole

called its event horizon. Once mass, or even light, passes within the event

horizon of a black hole, it cannot escape the black hole's gravitational

clutches.

The researchers think their development could aid scientists who are building

computer simulations of black holes and aiming to align them with observations

of actual black holes.

Astronomers think most galaxies, including our own Milky Way, host supermassive

black holes in their centers. Some researchers suspect that these are actually

Kerr black holes.

Valiente Kroon and Backdahl detail their work in the Jan. 19 issue of the

journal Proceedings of the Royal Society A.