Dolgachev surface

In mathematics, Dolgachev surfaces are certain simply connected elliptic surfaces, introduced by Igor Dolgachev (1981). They can be used to give examples of an infinite family of homeomorphic simply connected compact 4-manifolds, no two of which are diffeomorphic.

The blowup ${\displaystyle X_{0}}$ of the projective plane in 9 points can be realized as an elliptic fibration all of whose fibers are irreducible. A Dolgachev surface ${\displaystyle X_{q}}$ is given by applying logarithmic transformations of orders 2 and q to two smooth fibers for some ${\displaystyle q\geq 3}$.

The Dolgachev surfaces are simply connected, and the bilinear form on the second cohomology group is odd of signature ${\displaystyle (1,9)}$ (so it is the unimodular lattice ${\displaystyle I_{1,9}}$). The geometric genus ${\displaystyle p_{g}}$ is 0 and the Kodaira dimension is 1.

Simon Donaldson (1987) found the first examples of simply-connected homeomorphic but not diffeomorphic 4-manifolds ${\displaystyle X_{0}}$ and ${\displaystyle X_{3}}$. More generally the surfaces ${\displaystyle X_{q}}$ and ${\displaystyle X_{r}}$ are always homeomorphic, but are not diffeomorphic unless ${\displaystyle q=r}$.

Selman Akbulut (2012) showed that the Dolgachev surface ${\displaystyle X_{3}}$ has a handlebody decomposition without 1- and 3-handles.