Black holes, the cosmic giants, have long captivated scientists and the public alike. Their extreme density creates a point of no return, the event horizon, beyond which nothing, not even light, can escape. But these cosmic behemoths lie even more extreme objects – extremal black holes.

For half a century, extremal black holes were considered impossible. This belief came from a 1973 hypothesis on Black hole discovery by Stephen Hawking, John Bardeen, and Brandon Carter, stating that black hole surface gravity couldn't reach zero in a finite time frame, a condition necessary for an extremal black hole to form.

In a recent study, Mathematicians Christoph Kehle of MIT and Ryan Unger of Stanford and UC Berkeley challenged this long-held assumption. They demonstrate that nothing in our current understanding of physics prevents the formation of extremal black holes.

"This is a beautiful example of math giving back to physics," said Elena Giorgi, a mathematician at Columbia University.

Kehle and Unger stumbled upon this discovery while studying the formation of charged black holes. They realized their calculations allowed for black holes with any charge-to-mass ratio, including the extreme case of maximum charge.

The two scientists created a model where a non-rotating, uncharged black hole was bombarded with pulses from a charged particle field. By carefully tuning the frequency and intensity of these pulses, they could increase the black hole's charge faster than its mass, ultimately creating an extremal black hole.

Their work also addressed a long-standing fear – that forming an extremal black hole would create a 'naked singularity', a hypothetical object without an event horizon, which many physicists believe cannot exist.

Kehle and Unger's model showed that exceeding the extremal threshold would simply prevent the black hole from forming instead of a naked singularity.

While this mathematical proof doesn't guarantee the existence of extremal black holes in the universe, it opens up tantalizing possibilities.

"Just because a mathematical solution exists... doesn't necessarily mean that nature will use it," said physicist Gaurav Khanna of the University of Rhode Island. "But if we somehow find one, that would really make us think about what we are missing."

The implications of finding an extremal black hole are profound. It could revolutionize our understanding of the universe and push the boundaries of physics. Kehle and Unger are now focusing on the more mathematically challenging task of proving the existence of extremal black holes with maximum spin, a feat that could be even more revealing.

This discovery is a stark reminder that the universe is full of surprises. It compels us to keep exploring, questioning, and remaining open to the possibility that even our most firmly held-scientific beliefs may be overturned.

The universe, it seems, is a whole of wonders waiting to be unveiled by those brave enough to venture into the extreme.

The original story is published in  Quanta Magzine