1. A rotor for a compressor, the rotor having predetermined material characteristics and the compressor having predetermined operating conditions, the rotor comprising:
a circumferential recess including side walls and two shoulders formed in said side walls, each shoulder having a shoulder depth;
a plurality of rotor blades arranged as a rim around a rotation axis of the rotor, each blade including a blade root which holds the rotor blades in the rotor circumferential recess;
wherein each blade root includes a widening lower part which engages behind the two shoulders of the side walls;
wherein the depth of the recess is substantially greater than a minimum recess depth (T
min) such that the rotor has sufficient strength in the area of the blade attachment for starting based on said predetermined material characteristics of the rotor and the operating conditions of the compressor;
wherein the shoulder depth is sized to correspond to the recess depth, and wherein the rotor blade roots are sized to correspond to the recess depth.