The supersonic winds produced by massive stars carry a large amount of kinetic power .
In numerous scenarios such winds have been proven to produce shocks in which relativistic particles are accelerated emitting non-thermal radiation .
Here , we report the first detection of non-thermal emission from a single stellar bubble , G2.4+1.4 , associated with a WO star .
We observed this source with the uGMRT in Band 4 ( 550 - 850 MHz ) and Band 5 ( 1050 - 1450 MHz ) .
We present intensity and spectral index maps for this source that are consistent with synchrotron emission ( average spectral index , \alpha = -0.83 \pm 0.10 ) .
The fraction of the available kinetic wind power that is converted into cosmic ray acceleration is estimated to be of the order of a few per cent .
This finding constitutes an observational breakthrough and gives new insight on the non-thermal physical processes taking place in the environments of isolated massive stars .
In particular , our results show that non-runaway isolated massive stars are capable of accelerating relativistic particles and are therefore confirmed as sources of Galactic cosmic rays .