Within galaxies, powerful streams of energetic particles move, generated by the stellar winds of massive stars or by the gravitational effects of supermassive black holes; they are galactic winds. In some galaxies where the rate of star formation is high, winds emanating from supernovae can collide and transform, forming powerful bubbles of ultra-energetic particles called "galactic superwinds".
Not all galaxies are alike. Beyond their morphology, another parameter, among others, makes it possible to distinguish them:the rate of star formation. While some of them form very few stars, others have an extremely high formation rate; these are starburst galaxies.
In the latter, stellar winds — that is, the fluxes of particles emitted by stars — are more frequent. When these particle streams originate from very massive stars, spiral density waves, or supermassive black holes, they are defined as galactic winds.
Related topic:Supermassive black holes generate winds that shape all their galaxies
The most powerful of these galactic winds (essentially coming from supernovae) can collide, and when the shock at the interface of the flows is strong enough, the kinetic energy of the particles can be transformed into thermal energy (it is thermalized). This violent conversion prevents the vast majority of the energy involved from being freely emitted into space.
The shock then forms an extremely dense and hot gas bubble whose internal pressure is high. The bubble then expands, absorbing gases and particles from the intergalactic environment.
Inside the structure, the winds continue to collide, producing thermal shocks increasing the speed of expansion of the bubble. The surrounding intergalactic gas is either destroyed by the hydrodynamic processes of the phenomenon, or evaporates by thermal conduction, cooling the propagation medium of the bubble.
These galactic superwinds can thus extend from one end of the galaxy to the other. Theoretical models consider them essential in the processes of galactic evolution, in the sense that these super-winds eject large quantities of materials - in particular metals - in the galactic halo, thus making it possible to enrich the environment in elements necessary for the formation of stars and planets.
