We show that the recently developed thermal model which successfully describes how jets are launched by young stellar objects , when applied to system containing disk-accreting white dwarfs naturally explain the otherwise surprising absence of jets in cataclysmic variable stars .
Our main argument uses the crucial element of the thermal model , namely that the accreted material is strongly shocked due to large gradients of physical quantities in the boundary layer , and then cools on a time scale longer than its ejection time from the disk .
In our scenario the magnetic fields are weak , and serve only to recollimate the outflow at large distances from the source , or to initiate the shock , but not as a jet-driving agent .
Using two criteria in that model , for the shock formation and for the ejection of mass , we find the mass accretion rate above which jets could be blown from accretion disks around young stellar objects and white dwarfs .
We find that these accretion mass rates are \dot { M } ( { YSO } ) \ga 10 ^ { -7 } M _ { \odot } \leavevmode \nobreak yr ^ { -1 } and \dot { M } ( { WD } ) \ga 10 ^ { -6 } M _ { \odot } \leavevmode \nobreak yr ^ { -1 } 
for young stellar objects and white dwarfs respectively .
Considering the uncertainties of the model , these limits could overestimate the critical value by a factor of \sim 10 .