In mathematics, Dolgachev surfaces are certain simply connected elliptic surfaces, introduced by 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.
Properties
The blowup X0 of the projective plane in 9 points can be realized as an elliptic fibration all of whose fibers are irreducible. A Dolgachev surface Xq is given by applying logarithmic transformations of orders 2 and q to two smooth fibers for some q ≥ 3.
The Dolgachev surfaces are simply connected and the bilinear form on the second cohomology group is odd of signature (1, 9) (so it is the unimodular lattice I1,9). The geometric genus pg is 0 and the Kodaira dimension is 1.
Donaldson (1987) found the first examples of homeomorphic but not diffeomorphic 4-manifolds X0 and X3. More generally the surfaces Xq and Xr are always homeomorphic, but are not diffeomorphic unless q = r.
Akbulut (2008) showed that the Dolgachev surface X3 has a handlebody decomposition without 1- and 3-handles.