Timescale for different cooling losses in years (synchrotron, invere Compton, ionization and bremsstrahlung) as a function of the ISM density in cm^-3 at z = 0 for a cosmic ray energy of 1 GeV, a magnetic field strength of 10 μG and a radiation field of 10^-12 erg cm^-3 as typical for the Milky Way. The timescales are evaluated at the frequency ν_c corresponding to the peak synchrotron emission.