Stable Singularity Formation for the Keller-Segel System in Three Dimensions

We consider the parabolic-elliptic Keller-Segel system in dimensions d >= 3, which is the mass supercritical case. This system is known to exhibit rich dynamical behavior including singularity formation via self-similar solutions. An explicit example was found more than two decades ago by Brenner et al. (Nonlinearity 12(4):1071-1098, 1999), and is conjectured to be nonlinearly radially stable. We prove this conjecture for d = 3. Our approach consists of reformulating the problem in similarity variables and studying the Cauchy evolution in intersection Sobolev spaces via semigroup theory methods. To solve the underlying spectral problem, we use a technique we recently established in Glogic and Schorkhuber (Comm Part Differ Equ 45(8):887-912, 2020). To the best of our knowledge, this provides the first result on stable self-similar blowup for the Keller-Segel system. Furthermore, the extension of our result to any higher dimension is straightforward. We point out that our approach is general and robust, and can therefore be applied to a wide class of parabolic models.