Kerr vs Schwarzschild Black Holes
Schwarzschild: the simplest black hole model
The Schwarzschild solution describes an idealized black hole that is non‑rotating and uncharged. It’s the cleanest starting point for learning ray tracing and gravitational lensing because it is spherically symmetric.
Kerr: rotating black holes
The Kerr solution describes an idealized rotating black hole. Rotation breaks perfect spherical symmetry and introduces new structure (including frame dragging and the ergosphere). Many real astrophysical black holes are expected to have some rotation, so Kerr physics is important—just also mathematically more complex.
Frame dragging
In Kerr spacetime, the rotation of the black hole “drags” spacetime itself. A common intuition is: close to the hole, even if you try to “stand still,” spacetime has a preferred swirling direction.
For images, the practical consequence is that light paths can be skewed: the lensing is not perfectly symmetric in the same way as Schwarzschild.
Ergosphere
The ergosphere is a region outside the event horizon where frame dragging is so strong that no observer can remain stationary relative to distant stars. It is not the same as the event horizon.
You may see it discussed alongside the Penrose process (energy extraction) in advanced treatments. If you’re early in the learning path, focus first on horizons, photon spheres, and lensing.
What you should expect in visuals and simulations
Many educational renderers (including simpler black hole “image warp” simulators) approximate lensing with a Schwarzschild-like model, because it already captures the core: strong bending, rings, repeated structure, and a shadow region.
- Black hole image simulation (good for lensing intuition)
- Gravitational lensing (chapter)
- Event horizon vs photon sphere vs singularity
FAQ
- Are real black holes Kerr or Schwarzschild? Likely closer to Kerr (rotating), though the amount of spin varies and modeling depends on environment.
- Does rotation change the event horizon? Yes—Kerr horizons differ from the Schwarzschild case and come with additional structure (like the ergosphere).
- Do Kerr black holes always look “different” in pictures? Often the biggest visible differences are asymmetries in lensing and brightness, especially with realistic accretion disks and viewing angles.