Astronomers have debunked the well-known Kerr hypothesis regarding rotating black holes.

A black hole is formed either as a result of the "collapse" of a massive stellar core (a stellar-mass black hole), or from the merging of heavy objects (such as pairs of neutron stars), along with the subsequent absorption of a vast amount of matter, including other black holes (supermassive black holes at the centers of galaxies).

What happens to all that mass inside, and what occurs within a black hole concerning space-time: astrophysicists are boldly attempting to calculate and understand it mathematically. Most scientists rely on Albert Einstein, who in his General Theory of Relativity explained how the Earth and other planets orbit around the Sun, and how the entire Solar System orbits around the black hole at the center of our galaxy (it is important to clarify that this rotation occurs around a common center of gravity, the center of mass).

According to Einstein, the essence of the matter is that any mass-bearing substance distorts the fabric of space-time. When it concentrates in one location, a "funnel" is created there, into which everything is drawn, like a whirlpool. Based on this, astrophysicists strive to continue to illustrate this scenario inside the so-called event horizon — the conditional "surface" of the black hole.

In 1963, New Zealand mathematician Roy Kerr proposed his version. He calculated the physics of a rotating black hole, which aligns closely with what is observed in space: most stars rotate around their axes, suggesting that their collapsing cores should behave similarly. Moreover, everything in galaxies is known to swirl around. Interestingly, astrophysicists recently calculated that our central galactic black hole, Sagittarius A*, spins almost at the limit of its physical capabilities.

But what should happen inside? In Kerr's black hole, the event horizon is not the only or final horizon. It is merely a point of no return. From there, nothing can escape, but space-time still exists up to a certain limit. There are even suspicions that a person could survive after crossing the event horizon of Sagittarius A*: according to some hypotheses, they would not be torn apart immediately, while others suggest they would remain intact.

An inner second horizon of the black hole is proposed — the so-called Cauchy horizon (a term introduced by Penrose and Hawking in 1966). The singularity lies within its bounds. According to scientists, for distant observers, it would appear as a disk lying in the equatorial plane of the black hole. It is generally believed that space-time ceases to exist there, at least in the form we can understand. However, in 2018, mathematicians Michalis Dafermos and Jonathan Luke stated that it does exist there, but "not smoothly enough" for Einstein's equations to operate.

Now, new research from astrophysicists in Denmark, the Czech Republic, Italy, and New Zealand seems to challenge the entire Kerr concept. As they explained in their article for Physical Review Letters, the inner horizon of a black hole cannot endlessly accumulate energy: at some point, a certain limit must be reached, after which the black hole can no longer remain stable. According to the scientists, this means that "consuming" black holes cannot exist for very long. This contradicts observations.

For instance, at Cambridge University, it was established that the black hole at the center of the galaxy M87 (the one that was "first photographed," although in reality, it was just its "shadow") is almost as old as the universe itself: it is over 13 billion years old. It was only possible to "photograph" it because of the glowing matter it "consumes" — the so-called accretion disk. Estimates suggest that every ten years, a mass equivalent to a whole Sun falls into it. Throughout its existence, it has managed to accumulate a mass of more than six billion Suns.