Hot gas spirals inward, falling onto an invisible superdense object. Such a disk resembles a giant whirlpool, but it is often tilted: its axis does not align with the rotation axis of the central body. The gravity of the massive object makes the disk wobble slightly, like a spinning top losing its balance. For the first time, physicists have derived an equation describing this tilt with all the subtleties of general relativity.
Earlier calculations simplified the problem by assuming slow rotation. The new work covers any speed — from moderate to extreme, including so-called naked singularities. These are objects without an event horizon, where spacetime curvature becomes infinite but is not hidden behind a 'surface of no return.' It turns out that for naked singularities, the disk bends into a characteristic hump — where the gas rotation nearly stops. A black hole has no such hump.
This difference is not just a mathematical curiosity. The disk's tilt alters the X-ray glow that telescopes capture. By analyzing the spectrum and polarization, astronomers can peer into the heart of a galaxy and determine whether they are dealing with a black hole or a more exotic object. The method is not foolproof, but combined with other data, it becomes a powerful tool.
Naked singularities have not been discovered yet, but if they exist, they spin faster than any possible black hole.
In Alastair Reynolds's novel 'Revelation Space,' mysterious objects with naked singularities serve as a key to the secrets of vanished civilizations.