RADIATIVE COOLING INSTABILITY IN 1D COLLIDING FLOWS

Radiative shock waves show a strong cooling instability at temperature s above approximately 2 . 10(5)K. We numerically investigate this inst ability by simulating different astronomical objects in which collidin g flows play an outstanding role: Wind bubbles, supernova remnants, an d colliding winds. Computing the flow of each object over a large part of its evolutionary time and resolving all physically relevant scales , we find several phenomenologically different types of this instabili ty. If two smooth flows collide, the instability follows a periodic li mit cycle with two modes being important. The connection between the r adiative loss function and the mode and type of the over-stability is discussed. The collision of non-smooth flows can temporarily result in an aperiodic evolution of the system. After a characteristic relaxati on time the instability then becomes periodic again. Such disturbances as well as violent types of the instability can excite oscillations o f the thin layer of cold compressed gas downstream of the shock, which in turn can influence the stability of the radiative shock.