Black holes shed light on galaxy formation

For example, scientists are only beginning to accurately measure the speed at which a black hole rotates, a property called spin. This value is crucially important for understanding black holes. Scientists can completely characterize the motions of a black hole if its mass and spin are known.

The mystery of matter
“We know of no other object that is as simple as a black hole except for an elementary particle such as an electron,” said Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics.

Scientists have been measuring black hole masses for more than 30 years, but clocking the spin of one has proved much more difficult. Last fall, however, a team led by McClintock and his colleague Ramesh Narayan announced they had reliably measured the speed of one black hole 35,000 light-years away. They calculated the spin to be an astounding 950 spins per second — just below the theoretical rotation limit of 1,150 spins per second.

“We expect to determine a dozen black hole spins during the next several years,” McClintock told SPACE.com.

The questions keeping black hole researchers up at night aren’t necessarily new. Some have been around since black holes were first predicted.

“The single biggest mystery is: What is the state of matter at the center of a black hole?” Ghez said. “Our physical description of the universe breaks down at the center of a black hole.”

For example, current black hole theory states that gravitational forces inside a black hole reach infinity. But this almost certainly can’t be correct.

Infinity falls short
“Any time things go to infinity in physics, we know we haven’t gotten it right,” Ghez said in an e-mail interview.

The center of a black hole is known as the singularity. Theory predicts it is far smaller than an atom, yet contains all the mass and rotation of a star. Even for scientists who study black holes for a living, this idea is still mind-boggling.

“Can you imagine your car, the Earth, the Sun, or a billion suns being crushed by gravity to a point too small to view with any microscope?” McClintock said. “How can all the forms and matter around us, and the atoms of which they are composed, disappear into a massive, spinning point?”

Many scientists suspect that fundamental black hole questions like these won’t be answered until quantum mechanics and general relativity, the theories that describe how gravity works at the smallest and biggest scales of the universe, are reconciled.

“What really happens at the black hole event horizon? Or in the central singularity? Solving that would likely require, or lead to, some fundamental new physics, perhaps on par with general relativity theory itself,” said George Djorgovski of Caltech.

New ground and space-based instruments expected to go online in the coming years could help answer some of these questions and, in doing so, reveal something fundamental about the universe.

“Historically, any time we have learned something new about gravity, our understanding of the universe has been changed in profound ways," Reynolds said. "There is no reason to believe that this time would be any different.”

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