The triggering of star formation, as well as its quenching, is regulated by massive young stars in galaxies that inject energy & momentum into interstellar medium. Feedback from supermassive black holes in galaxy nuclei playes same important role. These processes result in the massive outflows of gases observed in galaxies, for example. However, the details, including how they work & relative roles of the different feedback processes, are actively discussed.
Cosmic rays in particular are accelerated in strong shocks formed by super nova explosions & stellar winds (two aspects of star formation) & generate considerable pressure in interstellar medium. They play a central role in regulating thermal equilibrium in the dense molecular clouds where most stars form and can play an important role in regulating star formation, driving galactic winds & even the determination of the character of intergalactic environment.
Astronomers believe that a key property that limits the influence of cosmic rays is the ability to propagate from the sites where they are produced into interstellar medium & beyond the disk, but the details are not well understood. .
CfA astronomer Vadim Semenov & 2 collaborators used computer simulations to explore how such variation in cosmic ray propagation may affect star formation in galaxies, prompted by recent observations of gamma ray emission from near sources of cosmic rays, including star clusters & supernova remnants. The observations probe the propagation of cosmic rays, because a large fraction of the gamma ray emission is thought to be produced when cosmic rays interact with interstellar gas. The observed gamma ray fluxes suggest that the propagation of cosmic rays near such sources can be locally suppressed by a significant factor, up to several orders of magnitude. Theoretical work suggests that such suppression may result from nonlinear interactions of cosmic rays with magnetic fields & turbulence.
Scientists have used simulations to probe for effects of suppressing cosmic rays transport near sources. They find that the suppression causes a build-up of local pressure & produces strong pressure gradients that prevent formation of massive molecular clumps of gas that form new stars, qualitatively changing global distribution of star formation, especially in massive, gas-rich galaxies that are prone to clump formation. They conclude that this cosmic ray effect regulates the development of galaxy’s disk & is an important complement to other processes active in galaxy formation.
The research published in The Astrophysical Journal.