Black holes are some of the most fascinating objects in the universe.
They are formed entirely from gravity, simple in appearance but hiding mysteries that challenge the laws of physics.
While scientists have learned a lot about the outer regions of black holes, their inner workings remain a puzzle.
A new study, published in Physical Review Letters, questions a long-standing theory about how black holes behave internally.
The research was conducted by an international team of scientists from Denmark, Italy, New Zealand, and the Czech Republic. Their findings suggest that our understanding of black holes, based on a widely accepted model called the Kerr solution, might need to be revised.
The Kerr solution, derived from Einstein's theory of General Relativity, is the standard model for describing rotating black holes.
It portrays black holes as regions of warped spacetime with two key features: an outer horizon, beyond which nothing -- not even light -- can escape, and an inner horizon, which surrounds a ring-like singularity where the rules of physics break down.
This model has been effective at explaining observations of black holes so far.
However, the study points out a major issue.
For years, scientists knew that the inner horizon in static black holes (those not spinning) would experience an infinite buildup of energy. Now, the researchers show that even in more realistic, spinning black holes, the inner horizon becomes unstable over time. Energy builds up exponentially until it reaches a massive value, potentially reshaping the black hole's structure.
"This means black holes may not settle into the stable shape described by the Kerr solution over their lifetimes," says Stefano Liberati, a professor at SISSA in Italy and one of the study's authors. "Our findings suggest the Kerr model may not fully explain the black holes we observe."
The researchers say this instability could have profound effects on the overall geometry of a black hole. While it's unclear exactly what happens after this energy buildup, it's possible that the black hole undergoes significant changes, challenging long-held assumptions.
"This study shows that the interior dynamics of black holes could radically change how we understand these objects, even from the outside," says Raúl Carballo-Rubio, a researcher at the University of Southern Denmark.
These findings open new doors for studying black holes. By understanding their internal dynamics better, scientists hope to refine their models and even connect these discoveries to potential observations of physics beyond Einstein's General Relativity.
The researchers emphasize that while their work raises big questions, it also offers exciting opportunities. Exploring the unstable interiors of black holes may eventually unlock some of the universe's greatest mysteries.